Biscuit Baking Technology: Processing and Engineering Manual [3 ed.] 0323999239, 9780323999236

Table of contents :
Biscuit Baking Technology
Introduction
Copyright
Contents
About the author
Iain Davidson, Director, Baker Pacific Ltd.
Baker Pacific Ltd.
Experience in the biscuit industry
Acknowledgements
1 The biscuits, cookies and crackers
1.1 The biscuits, cookies and crackers
1.2 Crackers
1.3 Soda crackers: process for sponge and dough
1.3.1 Description
1.3.2 Product specification
1.3.3 Formulation
1.3.4 Critical ingredients
1.3.5 Mixing and fermentation
1.3.6 Dough forming
1.3.7 Baking
1.3.8 Oil spray
1.3.9 Cracker breaking
1.4 Cream crackers: process for laminated crackers
1.4.1 Description
1.4.2 Product specification
1.4.3 Recipe
1.4.4 Dough mixing on a horizontal high-speed mixer
1.4.5 Preparation of the fat/flour for dusting
1.4.6 Lamination
1.4.7 Baking
1.5 Snack crackers
1.5.1 Process for snack crackers
1.5.2 Description
1.5.3 Product specification
1.5.4 Formulation
1.5.5 Critical ingredients
1.5.6 Mixing
1.5.7 Standing time
1.5.8 Forming
1.5.9 Baking
1.5.10 Baking band
1.6 Semi-sweet biscuits
1.6.1 Process for semi-sweet biscuits
1.6.2 Description
1.6.3 Product specification
1.6.4 Formulation
1.6.5 Critical ingredients
1.6.6 Mixing
1.6.7 Forming
1.6.8 Baking
1.6.9 Cooling
1.7 Process for Golden Maria or Dorada
1.7.1 Description
1.7.2 Product specification
1.7.3 Formulation
1.7.4 Mixing
1.7.5 Dough forming
1.7.6 Baking
1.8 Short doughs: rotary moulded biscuits
1.8.1 Process for moulded short dough biscuits
1.8.2 Description
1.8.3 Product specification
1.8.4 Formulation
1.8.5 Critical ingredients
1.8.6 Mixing
1.8.7 Standing time
1.8.8 Rotary moulding
1.8.9 Baking
1.8.10 Cooling
1.8.11 Process for ginger biscuits
1.8.12 Description
1.8.13 Product specification
1.8.14 Formulation
1.8.15 Process for ginger crunch biscuits
1.9 Cookies
1.10 Process for a chocolate chip cookie
1.10.1 Description
1.10.2 Product specification
1.10.3 Formulation
1.10.4 Mixing
1.10.5 Forming
1.10.6 Baking
1.10.7 Cooling
1.11 Sandwich biscuits
1.11.1 Description
1.11.2 Recipes for creams
1.11.3 Process for sandwich production
1.12 Long shelf life cakes, snack cakes
1.12.1 Process for Jaffa cakes
1.12.2 Product specification
1.12.3 Mixing
1.12.4 Baking
1.12.5 Cooling and jam depositing
1.12.6 Recipes
1.13 Summary
References
2 Baking process
2.1 From the dough piece to the biscuit
2.1.1 Biscuit structure
2.1.2 Moisture content
2.1.3 Colour
2.2 Ingredients
2.2.1 Wheat flour
2.2.2 Wheat flours: typical specifications
2.2.2.1 Wheat gluten
2.2.2.2 Starch
2.2.3 Sugar
2.2.4 Leavening agents
2.2.4.1 Yeast
2.2.4.2 Sodium bicarbonate (“soda”)
2.2.4.3 Ammonium bicarbonate (“vol”)
2.2.5 Fats
2.3 Baking process
2.3.1 Development of the biscuit structure and texture
2.3.2 Moisture removal
2.3.3 Colour
2.3.4 Summary
References
3 Baking profiles
3.1 Crackers
3.1.1 Structure
3.1.2 Moisture content
3.1.2.1 Latent heat of evaporation: 539kcal/kg
3.1.3 Colour
3.1.4 Oven specification
3.1.5 Baking profile
3.2 Snack crackers
3.2.1 Structure
3.2.2 Baking process
3.2.3 Moisture content
3.2.4 Colour
3.2.5 Baking times and temperatures
3.2.6 Baking profile
3.3 Semi-sweet biscuits
3.3.1 Structure
3.3.2 Moisture content
3.3.3 Colour
3.3.4 Oven specification
3.3.5 Baking profile
3.4 Short dough biscuits
3.4.1 Structure
3.4.2 Moisture content
3.4.3 Colour
3.4.4 Oven specification
3.4.5 Baking profile
3.5 Cookies
3.5.1 Structure
3.5.2 Moisture content
3.5.3 Colour
3.5.4 Oven specification
3.5.5 Baking profile
References
4 Biscuit design and output
4.1 Cutter and moulding roll layouts
4.2 Scrap and scrapless designs
4.3 Semi-sweet biscuits
4.4 Short dough biscuits and cookies
4.5 Docker pins
4.6 Oven band loadings
4.7 Oven size and output
4.7.1 Output calculation
4.8 Summary
Further reading
5 Heat transfer
5.1 Radiation
5.1.1 Wavelength
5.1.2 Radiant heat transfer
5.1.3 Distance
5.1.4 Effect of radiation on the dough pieces
5.1.5 Radio-frequency baking
5.1.6 Near-infrared baking
5.1.7 Microwave
5.2 Conduction
5.2.1 Baking with conduction
5.2.2 Oven insulation
5.3 Convection
5.3.1 Convection baking
5.4 Summary
5.4.1 Radiation
5.4.2 Conduction
5.4.3 Convection
Further reading
6 Oven designs
6.1 Heat transfer methods
6.1.1 Radiant heating
6.1.2 Conduction heat transfer
6.1.3 Convection baking
6.2 Radiant heating
6.2.1 Direct gas-fired ovens
6.2.2 Conversion to electrical heating
6.2.3 Summary
6.2.4 Electric ovens
6.2.5 Summary
6.2.6 Indirect radiant ovens
6.2.7 Summary
6.3 Turbulence systems
6.4 Conduction heat transfer
6.5 Convection baking
6.5.1 Direct convection ovens
6.5.2 Indirect convection ovens
6.5.3 Summary
6.5.4 ‘Re-circ’ ovens
6.5.5 Summary
6.6 Hybrid ovens
6.6.1 Direct gas-fired/indirect radiant ovens
6.6.2 Direct gas-fired/convection ovens
Further reading
7 Oven specifications
7.1 Specifications for ovens: crackers
7.1.1 Development of structure and texture
7.1.2 Reducing moisture content
7.1.3 Colour
7.1.4 Final moisture content
7.1.5 Recommended specification for a cracker oven
7.2 Recommended oven specification for light carrier products, for example crispbreads, rusks
7.3 Recommended oven specification for semi-sweet biscuits, for example Marie
7.4 Recommended oven specification for short dough biscuits
7.5 Specifications for ovens: soft dough cookies
7.6 Danish butter cookies
7.7 Modular oven design
7.8 Calculation of oven zone lengths
7.8.1 Example 1: Direct gas-fired oven for baking crackers (1.5×100m long)
7.8.1.1 Heat input
7.8.2 Example 2: Indirect radiant oven for baking a short dough biscuit, glucose type (1.25m×100m long)
7.8.2.1 Heat input
7.8.3 Example 3: Multipurpose oven 1.25m×91.0m
Additional information on sources
Biscuit oven manufacturers
Oven band manufacturers
Oven burner manufacturers
Heat flux technology
8 Oven construction: direct gas-fired ovens
8.1 Direct gas-fired baking chamber
8.1.1 Baking chamber construction
8.1.2 Conversion of gas-fired oven to electric
8.1.3 Materials
8.1.4 Dimensions
8.1.5 Expansion joints
8.1.6 Insulation
8.1.7 Oven return band covers
8.1.8 Explosion relief
8.1.9 Inspection doors
8.1.10 Cleanout doors
8.2 Extraction system
8.2.1 Fan specification
8.2.2 Extraction: oven end hood
8.3 Direct gas-fired oven: gas burner system
8.3.1 Gas train
8.3.2 Combustion air
8.3.3 Temperature control system
8.3.4 Flynn burners for direct gas-fired oven
8.3.5 Infrared metal fibre burners
8.3.6 Flynn infrared profile 7 distributor burner
8.4 Control panels
8.4.1 Main control panels
8.4.2 Control panel construction
Further reading
9 Oven construction: indirect radiant ovens
9.1 Indirect radiant baking chamber
9.1.1 Baking chamber construction and dimensions
9.1.2 Expansion joints
9.1.3 Heater module
9.1.4 Radiant tubes
9.1.5 Return ducts
9.1.6 Circulation fan
9.1.7 Extraction and turbulence
9.1.8 Heat exchanger flue (chimney)
9.1.9 Explosion relief
9.1.10 Insulation
9.1.11 Inspection doors
9.1.12 Cleanout doors
9.2 Indirect fired ovens: burners
9.2.1 Weishaupt burners
9.2.1.1 Technical description
9.2.1.2 Specification: Weishaupt burner WG30N/1-C ZM LN (for 1.25m wide indirect radiant oven)
9.2.2 Maxon burners
9.2.2.1 Specification for 1.2m wide indirect radiant oven
9.2.2.1.1 Maxon OVENPAK 515 gas/oil burner
9.2.2.1.2 Maxon gas pipe trains
9.2.2.1.3 Pilot gas train
9.2.2.1.4 Oil pipe train
9.2.2.1.5 Compressed air train
Further reading
10 Heat recovery system
10.1 Heat recovery system
10.1.1 Calculations of hot air flow to the HRS zone
Further reading
11 Oven construction: convection ovens
11.1 Direct and indirect convection systems
11.2 Baking chamber
11.2.1 Baking chamber construction
11.2.2 Convection plenums
11.2.3 Return air
11.2.4 Circulation fan
11.2.5 Heater module
Further reading
12 Oven construction: electric ovens
12.1 Electric oven construction
12.2 Electrical elements
12.3 Conversion of direct gas-fired oven to electrically heated oven
12.4 Oven efficiency
12.5 Ovens with hot air circulation
12.5.1 Indirect radiant oven
12.5.2 Convection ovens
12.6 Control systems
Further reading
13 Oven conveyor bands (belts)
13.1 Rolled wire-mesh bands (belts)
13.1.1 Z-type bands
13.1.2 Wire-mesh bands: skid bar supports
13.1.3 Wire-mesh bands: support rollers
13.1.4 Return band supports
13.1.5 Wire-mesh oven band cleaning
13.1.6 Wire-mesh oven band tracking
13.1.7 Joining wire-mesh bands
13.1.8 Dimensions of rolled wire-mesh belts
13.2 Compound balanced weave bands
13.2.1 Compound balanced weave band supports
13.2.2 Band tracking for compound balanced weave bands
13.2.3 Joining Ashworth bands
13.2.4 Dimensions of compound balanced weave bands
13.3 Steel bands
13.3.1 Steel band supports
13.3.2 Joining steel bands
13.3.3 Steel band cleaners
13.3.4 Steel band greasing
13.3.5 Steel band tracking
Further reading
14 Oven conveyor design
14.1 Oven conveyor
14.2 Feed end
14.2.1 Oven terminal drums
14.3 Delivery end
14.3.1 Delivery end drum
14.3.2 Oven drive
14.3.3 Sprag clutch
14.3.4 Uninterruptible power supply
14.3.5 Stripping conveyor
14.3.6 Oven end hood design
14.3.7 Calculation of oven band tension
14.3.8 Calculation of torque required for the conveyor drive
14.3.9 Calculation of electric motor power
Further reading
15 Process control systems
15.1 Temperature control
15.1.1 Direct gas-fired ovens
15.1.2 Indirect radiant ovens
15.1.3 Convection ovens
15.1.4 Electric ovens
15.1.5 Temperature monitoring and control
15.1.6 Temperature controllers
15.1.7 PID control
15.1.8 Top and bottom temperature control
15.2 Baking time
15.3 Humidity
15.4 Colour control
15.4.1 Direct gas-fired ovens
15.4.2 Indirect radiant ovens
15.4.3 Colour measurement
15.5 PLC control
15.5.1 Specification for a PLC control system
Further reading
16 Oven safety monitoring and alarm
16.1 Oven band safety systems
16.1.1 Oven band tracking
16.1.2 Detection of the oven band position
16.1.3 Oven band drive
16.1.4 Emergency stops
16.1.5 Emergency oven band drive
16.1.6 Oven band tension system
16.2 Oven burners and gas system
16.2.1 Gas trains
16.2.2 Gas system
16.2.3 Main gas solenoid valves
16.2.4 High-/low-pressure switch
16.2.5 Zero gas governor
16.2.6 Purge system
16.2.7 Over-temperature safety
16.3 Direct gas-fired ovens: manual control of top and bottom burners
16.3.1 Air system
16.3.2 Burner flame supervision
16.3.3 Gas/air mixture
16.4 Indirect-fired ovens: Weishaupt burners
16.4.1 Excess temperature
16.5 Extraction, combustion air and circulation fans
16.5.1 Damper controls
16.6 General safety equipment and instructions
16.6.1 Guards and safety devices
16.6.2 Operation safety precautions
16.6.3 Cleaning and maintenance safety precautions
16.6.4 Commissioning safety precautions
16.6.5 Running the equipment without safety systems
16.6.6 Protection of employees
16.6.7 Emergency shutdown
Further reading
17 Manufacture of biscuit ovens
17.1 Why build the oven locally?
17.2 Building baking ovens locally: the tasks and team
17.2.1 The team and experience required
17.3 Manufacturing drawings
17.4 Control and safety systems
17.5 Contractors
17.6 Purchasing
17.7 Shipping
17.8 Installation
17.9 Summary
Further reading
18 Oven operation: direct gas-fired oven
18.1 Starting the direct gas-fired oven: preparation
18.1.1 Baking programme
18.1.2 Burner pattern
18.1.3 Before starting the oven
18.2 Lighting the burners – direct gas-fired zone
18.3 Heating up/start of production
18.4 Shutting down the direct gas-fired oven
18.4.1 When temperature drops to 100°C
18.5 In the event of power failure
18.6 In an emergency
Further reading
19 Oven operation: indirect radiant oven
19.1 Preparation
19.1.1 Baking programme
19.1.2 Before starting the oven
19.2 Starting the oven
19.2.1 Controls and settings
19.2.2 Lighting the burners
19.2.3 Heating up/production
19.2.4 Damper controls
19.2.5 Zone heating controls
19.2.6 Extraction and turbulence dampers
19.3 Shutting down the indirect radiant oven
19.3.1 When temperature drops to 100°C
19.4 In the event of power failure
19.5 In an emergency
19.6 Control of the heat recovery system
Further reading
20 Oven efficiency
20.1 Energy use
20.2 Example of energy usage
20.2.1 Product and oven
20.2.2 Data from independent test results
20.2.3 Energy to bake the product
20.2.4 Heat loss from extraction from baking chambers
20.2.5 Heat loss from return band
20.2.6 Heat loss from the insulation and outer covers of the oven
20.2.7 Heat loss from oven delivery end
20.2.8 Heat loss from burner flues
20.2.9 From the calculations above, the energy consumption of the oven per hour
20.3 Comparison of oven efficiency for different oven types (based on actual installations)
20.4 Calculations for the energy required to bake biscuits
20.4.1 Rotary moulded biscuit
20.4.2 Semi-sweet biscuit
20.4.3 Cracker
References
21 Energy for biscuit baking
21.1 Combustion data: natural gas
21.1.1 Combustion process
21.1.2 Carbon dioxide emission from burning natural gas
21.2 The biscuit industry carbon footprint
21.2.1 Climate change and greenhouse gases
21.2.2 Energy usage for baking
21.2.3 Consumption of gas for baking
21.2.4 The carbon footprint
21.2.5 Energy sources for biscuit baking
21.3 Generating electricity from renewable energy sources
21.3.1 Power generation costs for renewable energy
21.3.2 Development of electricity generation from renewables
21.3.3 Future developments for biscuit baking
21.4 Solar energy
21.4.1 New biscuit bakeries
21.4.2 Solar energy for a new bakery
Further reading
22 Oven inspection and audit
22.1 Oven performance
22.1.1 Output
22.1.2 Product specification/compliance
22.1.3 Energy usage
22.2 Oven band
22.3 Baking chamber
22.4 Gas and oil trains
22.5 Gas burners
22.5.1 Burners: direct gas-fired ovens
22.5.2 Burners: indirect-fired ovens
22.6 Temperature and humidity control systems
22.6.1 Heat flux
22.6.2 Measurement of heat flux
22.6.3 Baking temperature and humidity
22.7 Controls and electrical panels
22.8 Reporting
Further reading
23 Oven maintenance
23.1 Preparation
23.2 New equipment
23.3 Routine maintenance
23.3.1 Safety devices
23.4 Mechanical components
23.4.1 Welded components
23.4.2 Driving chains and belts
23.4.3 Motors and drives
23.4.4 Steam lines and fittings
23.4.5 Air lines and fittings
23.4.6 Seal and gaskets
23.4.7 Bearings
23.4.8 Conveyor belts
23.4.9 Oven band tension
23.4.10 Pneumatic tension arrangement
23.4.11 Band pressure switch
23.4.12 Oven band tracking
23.4.13 Bearings for oven band support rollers
23.4.14 Explosion panels
23.4.15 Oven flues
23.4.16 Pulleys for fans
23.4.17 Fans
23.5 Electrical maintenance
23.5.1 General
23.5.2 Cleaning
23.5.3 Relays
23.5.4 Inspection schedule for relays
23.5.5 Temperature controllers
23.5.6 Connections and leads
23.5.7 Fuses
23.5.8 Earth leakage protection devices
23.5.9 Clutches and brakes
23.5.10 Transistor/solid-state devices
23.5.11 Limit switches
23.5.12 Proximity detectors (inductive or capacitive)
23.5.13 Plug-in timers
23.5.14 Battery safety
23.6 Maintenance schedule
23.6.1 Each day
23.6.2 Each week
23.6.2.1 Driving belts
23.6.2.2 Fan filters
23.6.2.3 Inspection and access doors
23.6.2.4 Oven lamps
23.6.2.5 Dampers
23.6.2.6 Emergency drive
23.6.2.7 Oven ignition
23.6.2.8 Oven band
23.6.3 Every 12 months
23.6.3.1 Burners and gas equipment
23.7 Oven cleaning
23.8 Standard lubrication
23.8.1 Ball/roller bearings with provision for lubrication
23.8.2 Sealed ball bearings
23.8.3 NSK-RHP self lube bearings
23.8.4 Recommended lubricants
23.8.5 Every 200 h
23.8.6 Every 2500 h
23.8.7 Every 5000 h
23.8.8 Each year
23.9 Maintenance log or record
23.10 Recommended spare parts
23.10.1 Gas system
23.10.2 Weishaupt burners
23.10.3 Maxon burners
23.10.4 Flynn burners
23.10.5 Electrical/temperature control parts
23.10.6 Mechanical parts
References
Appendix 1 Ingredients for biscuits: an introduction
1 Flour
1.1 Wheat flour
1.2 Corn flour
2 Sugars and syrups
2.1 Sucrose
2.2 Glucose syrup
2.3 Cane syrup 80%
2.4 Invert syrup 70%
2.5 Fructose syrup 80%
2.6 Malt extract 80%
3 Fats
3.1 Dough fat
3.2 Butter
3.3 Palm oil
3.4 Coconut oil
4 Dairy products
4.1 Whole egg powder
4.2 SMP, FCMP—skimmed milk powder, full cream milk powder
5 Leavening agents
5.1 Yeast (fresh)
5.2 Ammonium bicarbonate (“Vol”) (NH4)HCO3
5.3 Sodium bicarbonate (“Soda”) NaHCO3
5.4 ACP—acid calcium phosphate
5.5 SAPP or PURON—sodium acid pyrophosphate
6 Emulsifiers
6.1 Lecithin
6.2 GMS—Glycerol monostearate
7 Flavour enhancers
7.1 Salt
7.2 Monosodium glutamate (MSG) C5H8NO4Na
7.3 SSL—sodium stearoyl lactylate
8 Preservative
8.1 SMS—Sodium metabisulphite Na2S2O5
9 Enzymes
9.1 Proteolytic enzymes
Bibliography
Appendix 2 Specification of a multi-purpose oven 1.27×91.9m
1 Oven feed end
2 Direct gas fired zone 31.9m long with three heat control zones
3 Direct gas fired burners and gas equipment
3.1 Gas train
3.2 Air supply
3.3 Burner system
3.4 Automatic temperature control
4 Indirect radiant oven
4.1 Oven burners
4.2 Gas train
4.3 Automatic temperature control
4.4 Turbulence/convection system
4.5 Thermocouples and pressure gauges
5 Oven band
5.1 Oven band cleaner
6 Delivery end section
6.1 Oven end extraction hood
7 Control panels
8 Oven safety systems
8.1 Oven band
8.2 Ignition
8.3 Purge system
8.4 Over temperature
8.5 Power failure
9 Components and finishes
9.1 Electrical installation
9.2 Components
9.3 Finishes
Bibliography
Appendix 3 Oven manufacturers
1 China
1.1 Dongguang Furong Food Machinery Factory
1.2 Evergrowing Food Machinery Co. Ltd
1.3 Shanghai Kuihong Food Machinery
1.4 Sinobake, Guandong Shunde Huaji Industrial Co
1.5 Skywin Foodstuff Machinery Co. Ltd
1.6 Zhongshan Dingson Food Machinery Ltd
1.7 Zhuhai Hong Fu Mechanical Manufacturing Co. Ltd
2 EUROPE
2.1 Aasted ApS
2.2 Baker Perkins Ltd
2.3 Baker Perkins Inc
2.4 Bühler Group
2.5 GEA IMAFORNI INT'L S.p.A
2.6 Laser Srl
2.7 Pek Makina
2.8 Polin, Ing POLIN E C. SpA
2.9 Senius Equipment Aps
2.10 Spooner Vicars Bakery Systems
2.11 TMFCT – Bonnand Lornac
2.12 Werner & Pfleiderer
3 India
3.1 Bake-o-Nomic Corp
3.2 Besto Oven Industries
3.3 Esspee Engineers, Kolkata
3.4 New Era Machines
3.5 Ovenman Industries Private Ltd
4 Japan
4.1 Misuzu Koki Co Ltd
4.2 Naigai-Vicars
5 Korea
5.1 Dong Yang Food Machinery Co. Ltd
6 United States
6.1 Baker Perkins Inc
6.2 Reading Bakery Systems
Appendix 4 Oven band manufacturers
1 Agrati La Bridoire Sarl
2 Ark Engineers
3 Ashworth Bros. Inc
4 Audubon
5 Berndorf Band Gmbh
6 Bharat Wire Mesh Company
7 Cambridge Engineered Solutions
8 Consol Machinery (Canton) Co. Ltd
9 Durgesh Industries
10 Heights Wire Belt Factory
11 IPCO
12 Rexnord Inc
13 Shri Jai Maharani Industry
14 Steinhaus GmbH
15 Yangzhou Jiangdu Huada Metal Mesh Belt Factory
16 Yangzhou Jinrun Mesh Belt Manufacturing Co
Index

Citation preview

BISCUIT BAKING TECHNOLOGY THIRD EDITION

BISCUIT BAKING TECHNOLOGY Processing and Engineering Manual THIRD EDITION IAIN DAVIDSON Director, Baker Pacific

Introduction Our book is way of sharing over 50 years of experience in the biscuit baking industry worldwide. As engineers, we have worked with firstclass food technologists, bakers and confectioners in Europe, North and South America, Africa, Asia and Australasia. Our customers have included the largest multi-nationals and many local businesses. You will find here technical information and recommendations regarding biscuit baking. These are offered to share experience which has been valuable for us. It is not the only way to bake and to build biscuit baking ovens, but it has worked well for us and many of the bakeries we served. Please note that the formulations and process information is highly dependent on the specification and properties of the local ingredients and the production equipment. All formulations and process have to be developed at the commissioning stage to suit local conditions. My experience has taught me that it takes a small team to build the ovens. At our company a team of five people developed the Baker Pacific ovens described in this book and managed the manufacture and installation of the ovens: a project manager, design engineer, installation engineer and commissioning engineer and a local manager to liaise with the local contractors. All manufacture has been carried out under contract by excellent engineering companies in China, India and Indonesia. We believe that this may increasingly become a feature of future biscuit oven supply. Larger biscuit makers with substantial production facilities and experience and investment in development may lead the way to future improvements in product quality and production efficiencies. Smaller local teams may manufacture and install the ovens. In this new edition, we draw attention to the energy used for baking. Currently, the biscuit baking industry worldwide uses gas and this creates a large carbon footprint. In the coming years electricity generated from renewable sources will become increasingly competitive and a preferable source of energy for baking. Our Baker Pacific Direct Gas Fired Ovens are now designed for future conversion to electric energy. Iain Davidson

xv

Academic Press is an imprint of Elsevier 125 London Wall, London EC2Y 5AS, United Kingdom 525 B Street, Suite 1650, San Diego, CA 92101, United States 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom Copyright © 2023 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. ISBN: 978-0-323-99923-6 For Information on all Academic Press publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Nikki Levy Acquisitions Editor: Nina Bandeira Editorial Project Manager: Aera Gariguez Production Project Manager: Sruthi Satheesh Cover Designer: Mark Rogers Typeset by MPS Limited, Chennai, India

Contents

About the author Acknowledgements Introduction

xi xiii xv

1. The biscuits, cookies and crackers

1

1.1 The biscuits, cookies and crackers 1.2 Crackers 1.3 Soda crackers: process for sponge and dough 1.4 Cream crackers: process for laminated crackers 1.5 Snack crackers 1.6 Semi-sweet biscuits 1.7 Process for Golden Maria or Dorada 1.8 Short doughs: rotary moulded biscuits 1.9 Cookies 1.10 Process for a chocolate chip cookie 1.11 Sandwich biscuits 1.12 Long shelf life cakes, snack cakes 1.13 Summary References

1 2 4 11 13 16 21 23 28 31 34 38 42 43

2. Baking process

45

2.1 From the dough piece to the biscuit 2.2 Ingredients 2.3 Baking process References

45 47 50 55

3. Baking profiles

57

3.1 Crackers 3.2 Snack crackers 3.3 Semi-sweet biscuits 3.4 Short dough biscuits 3.5 Cookies References

57 61 64 68 70 73

v

vi

Contents

4. Biscuit design and output

75

4.1 Cutter and moulding roll layouts 4.2 Scrap and scrapless designs 4.3 Semi-sweet biscuits 4.4 Short dough biscuits and cookies 4.5 Docker pins 4.6 Oven band loadings 4.7 Oven size and output 4.8 Summary Further reading

75 77 79 80 81 83 84 85 85

5. Heat transfer

87

5.1 Radiation 5.2 Conduction 5.3 Convection 5.4 Summary Further reading

87 95 98 99 101

6. Oven designs 6.1 Heat transfer methods 6.2 Radiant heating 6.3 Turbulence systems 6.4 Conduction heat transfer 6.5 Convection baking 6.6 Hybrid ovens Further reading

7. Oven specifications 7.1 Specifications for ovens: crackers 7.2 Recommended oven specification for light carrier products, for example crispbreads, rusks 7.3 Recommended oven specification for semi-sweet biscuits, for example Marie 7.4 Recommended oven specification for short dough biscuits 7.5 Specifications for ovens: soft dough cookies 7.6 Danish butter cookies 7.7 Modular oven design 7.8 Calculation of oven zone lengths Additional information on sources

8. Oven construction: direct gas-fired ovens 8.1 Direct gas-fired baking chamber 8.2 Extraction system 8.3 Direct gas-fired oven: gas burner system 8.4 Control panels Further reading

103 103 105 114 114 116 120 122

123 123 127 129 130 131 133 133 134 140

143 143 151 153 162 166

Contents

9. Oven construction: indirect radiant ovens 9.1 Indirect radiant baking chamber 9.2 Indirect fired ovens: burners Further reading

10. Heat recovery system 10.1 Heat recovery system Further reading

11. Oven construction: convection ovens 11.1 Direct and indirect convection systems 11.2 Baking chamber Further reading

12. Oven construction: electric ovens 12.1 Electric oven construction 12.2 Electrical elements 12.3 Conversion of direct gas-fired oven to electrically heated oven 12.4 Oven efficiency 12.5 Ovens with hot air circulation 12.6 Control systems Further reading

vii 167 167 179 185

187 187 193

195 195 197 200

201 201 202 205 205 205 207 209

13. Oven conveyor bands (belts)

211

13.1 Rolled wire-mesh bands (belts) 13.2 Compound balanced weave bands 13.3 Steel bands Further reading

211 222 227 234

14. Oven conveyor design 14.1 Oven conveyor 14.2 Feed end 14.3 Delivery end Further reading

15. Process control systems 15.1 Temperature control 15.2 Baking time 15.3 Humidity 15.4 Colour control 15.5 PLC control Further reading

235 235 235 240 252

253 253 260 260 262 266 271

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Contents

16. Oven safety monitoring and alarm 16.1 Oven band safety systems 16.2 Oven burners and gas system 16.3 Direct gas-fired ovens: manual control of top and bottom burners 16.4 Indirect-fired ovens: Weishaupt burners 16.5 Extraction, combustion air and circulation fans 16.6 General safety equipment and instructions Further reading

17. Manufacture of biscuit ovens 17.1 Why build the oven locally? 17.2 Building baking ovens locally: the tasks and team 17.3 Manufacturing drawings 17.4 Control and safety systems 17.5 Contractors 17.6 Purchasing 17.7 Shipping 17.8 Installation 17.9 Summary Further reading

273 273 277 279 282 284 284 286

289 289 291 293 296 297 298 298 299 300 300

18. Oven operation: direct gas-fired oven

303

18.1 Starting the direct gas-fired oven: preparation 18.2 Lighting the burners direct gas-fired zone 18.3 Heating up/start of production 18.4 Shutting down the direct gas-fired oven 18.5 In the event of power failure 18.6 In an emergency Further reading

303 307 308 308 308 308 309

19. Oven operation: indirect radiant oven

311

19.1 Preparation 19.2 Starting the oven 19.3 Shutting down the indirect radiant oven 19.4 In the event of power failure 19.5 In an emergency 19.6 Control of the heat recovery system Further reading

20. Oven efficiency 20.1 Energy use 20.2 Example of energy usage

311 312 318 318 318 319 321

323 323 324

Contents

20.3 Comparison of oven efficiency for different oven types (based on actual installations) 20.4 Calculations for the energy required to bake biscuits References

21. Energy for biscuit baking 21.1 Combustion data: natural gas 21.2 The biscuit industry carbon footprint 21.3 Generating electricity from renewable energy sources 21.4 Solar energy Further reading

22. Oven inspection and audit 22.1 Oven performance 22.2 Oven band 22.3 Baking chamber 22.4 Gas and oil trains 22.5 Gas burners 22.6 Temperature and humidity control systems 22.7 Controls and electrical panels 22.8 Reporting Further reading

23. Oven maintenance 23.1 Preparation 23.2 New equipment 23.3 Routine maintenance 23.4 Mechanical components 23.5 Electrical maintenance 23.6 Maintenance schedule 23.7 Oven cleaning 23.8 Standard lubrication 23.9 Maintenance log or record 23.10 Recommended spare parts References

Appendix 1: Ingredients for biscuits: an introduction Appendix 2: Specification of a multi-purpose oven 1.27 3 91.9 m Appendix 3: Oven manufacturers Appendix 4: Oven band manufacturers Index

ix 329 330 333

335 335 337 340 343 344

347 347 351 355 358 358 361 363 363 364

365 365 366 366 366 369 372 373 374 376 376 378

379 387 395 401 405

About the author

Iain Davidson, Director, Baker Pacific Ltd. Iain graduated from the School of Industrial Design (Engineering) at Royal College of Art in London in 1965 and joined Baker Perkins Ltd. He was an industrial design engineer, working in the Technical Department on the design of new biscuit, bakery and candy processing machines until 1975, gaining a thorough technical knowledge of the machines and processes. In 1975 Iain was appointed as market development manager at Baker Perkins, involved in developing the Baker Perkins’ forward planning for new business, product development and acquisitions. In 1979 Iain became international sales manager with responsibility for the biscuit business in Asia and Africa. In 1990 Iain was appointed as Regional Manager Asia Pacific for Baker Perkins and re-located to Indonesia and later in 1997 to China. His appointments included managing director of Baker Perkins (Hong Kong) Ltd. and director of Baker Perkins Japan KK. In 1990 Iain negotiated an agreement with the Liaoning Foreign Trade Corporation in Dalian to establish a manufacturing facility for biscuit ovens. This was successful in manufacturing ovens under the supervision of Baker Perkins Japan KK engineers.

Baker Pacific Ltd. In 2000 Iain left Baker Perkins Ltd. and established his own company in Indonesia, PT Baker Pacific Mandiri. The company provided consultancy in the biscuit and confectionery industries in Asia. As the business outside Indonesia grew, Baker Pacific Ltd. was established in Hong Kong in 2004, providing process technology and machinery for the biscuit, chocolate and candy industries. Baker Pacific Ltd. established a manufacturing capability for biscuit ovens and manufactured ovens in China, India and Indonesia. During recent years, Iain has provided training programs for technical staff in biscuit bakeries, both courses presented on site and also

xi

xii

About the author

provision of presentation materials for in-house programs. Iain completed the technical manual ‘Biscuit Baking Technology, 2nd Edition’ published in 2016 and Biscuit Cookie and Cracker Production in 2019 by Academic Press, an imprint of Elsevier. Biscuit, Cookie and Cracker Process and Recipes published in 2020 was co-authored with the late Glyn Barry Sykes.

Experience in the biscuit industry • Engineering design of biscuit process machines including a range of baking ovens • Biscuit baking oven manufacture in China, Indonesia and India • Sales and marketing of biscuit production equipment in Europe, Asia, North America and Africa • Project management and service for biscuit production lines • Preparation and presentation of training programs for technical staff

Acknowledgements

The book is based on over 50 years in the biscuit baking industry and includes the experience of many colleagues from Baker Perkins Ltd., the bakeries in which we worked and our suppliers and contractors. Stephen Eldridge has designed and provided all the manufacturing drawings for the Baker Pacific ovens shown in the book. The installation and commissioning of our ovens has been managed by the late John Lilley. I have been indebted to Kevin Orbell and Keith Graham at Baker Perkins for their continued support. I wish to thank the Acquisition Editor, Nina Bandeira, and all her team at Elsevier for making this book possible and for their exceptional support and guidance. Iain Davidson

xiii

C H A P T E R

1 The biscuits, cookies and crackers This book is primarily about the design, manufacture and operation of biscuit baking ovens. It covers the mechanical and electrical engineering of the ovens, the control systems and the efficiency of heat transfer, energy use and output. In the first chapter, we describe the range of biscuit types and the baking process. Our aim is to bake economically and efficiently high-quality products that consumers enjoy to eat.

1.1 The biscuits, cookies and crackers Biscuits, cookies and crackers are the first and the best snack food they need no preparation, are eaten straight from the pack, have a long shelf life, are nutritious and available in many functional forms. Biscuits, cookies and crackers are now a truly international food, consumed in large and increasing quantities in Asia, Australasia, Africa, Middle East, North, Central and South America, as well as their original source in Europe. The products broadly fall into six categories, distinguished by their recipes and process: crackers, snack crackers, semi-sweet biscuits, short dough biscuits, cookies (including filled cookies) and sandwich biscuits. Each category and each product type require a particular mixing, forming and baking process. An example is given of the formulation and process for a product in each main biscuit category.

Biscuit Baking Technology DOI: https://doi.org/10.1016/B978-0-323-99923-6.00015-6

1

© 2023 Elsevier Inc. All rights reserved.

2

1. The biscuits, cookies and crackers

The formulations, recipes and process information given are from commercially produced products. However, their exact details and use depend on the local ingredients and production equipment. In each case the recipes and process will require development during commissioning to suit the particular ingredients and equipment available. In general, the biscuit-making process follows the main steps shown below. Dough mixing and fermentation, or dough standing time is usually a batch process. The forming of the dough pieces, baking, oil spraying and cooling are continuous operations with a high degree of automation. Packaging is generally off line, unless the production line is dedicated to a single product for which fully automatic systems may be supplied (Fig. 1.1).

FIGURE 1.1 Production process.

1.2 Crackers Crackers are characterised by crispy, open texture and savoury flavours. Crackers include soda and saltine crackers, cream crackers, water biscuits, “Maltkist” (sugar-topped crackers), wholemeal and bran crackers, vegetable and calcium crackers (Fig. 1.2).

Biscuit Baking Technology

1.2 Crackers

3

FIGURE 1.2 Crackers.

In general, crackers have some of the following features which influence the baking process: • Doughs that are leavened and fermented with ingredients such as yeast, ammonium bicarbonate and sodium bicarbonate. • Doughs generally have a high water content (15% 25%).

Biscuit Baking Technology

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1. The biscuits, cookies and crackers

• Cracker doughs are laminated (the dough sheet is made up from multiple thin layers). • Cracker doughs spring or lift in the first part of the oven to achieve an open, flaky texture, this requires humidity and high radiant heat input. • Some crackers are cut and baked in strips or complete sheets and broken into individual biscuits after baking. • Some crackers require a colour contrast between dark blisters and a pale background colour. • Traditional English crackers such as cream crackers and water biscuits are normally baked on light wire-mesh bands. • Traditional American crackers, such as soda or saltine are baked on heavy compound balanced weave bands which are pre-heated to transfer heat rapidly by conduction into the dough pieces. • Crackers are baked to low moisture contents (1.5% 2.5%), which requires a high energy input.

1.3 Soda crackers: process for sponge and dough Refer Fig. 1.3.

FIGURE 1.3 Soda crackers.

1.3.1 Description Soda crackers are a traditional product in the United States, where it is made in very large volumes. Also known as saltine or premium crackers. They are often eaten as an accompaniment to food, particularly soups. Soda crackers are also popular in Latin America, the Philippines, China, Korea and Italy. A sponge and dough process is used with soda being added at the dough stage. This gives the product a strong alkali reaction after baking. A long fermentation time is used and this gives flavour development and a mellowing of the protein. Soda crackers are baked in a sheet without scrap and are normally broken into single biscuits or pairs. Biscuit Baking Technology

1.3 Soda crackers: process for sponge and dough

• A long fermentation in two stages, up to 24 h. • Fast baking time, around 2.5 min, on a pre-heated compoundbalanced weave oven band. • Soda crackers are baked in strips or sheets and are broken into individual crackers, (usually in pairs) after baking.

1.3.2 Product specification Dimensions:

91 3 44 mm

Thickness:

5.6 mm

Weight:

6.25 g

Appearance:

Evenly blistered

Colour:

Pale creamy colour with darker blisters, evenly spaced

Texture:

Open and flaky, with a crispy bite

Flavour:

Mild, fermented flavour

pH:

7.2 8.0

Moisture:

2.5%

1.3.3 Formulation Sponge

(1)

(2)

Flour (strong)

66.7

80.0

Fresh yeast

0.17

0.40

Dough fat

5.00

6.00

Lecithin

0.53

-

Malt extract 80%

0.95

0.60

Sugar

-

0.80

Water

28.0

24.0

Dough Sponge (as above) Flour (weak)

33.3

20.0

Dough fat

5.00

8.00

Soda

0.60

0.60

Salt

1.50

1.80

Biscuit Baking Technology

5

6

1. The biscuits, cookies and crackers

Enzyme

0.03

Ammonium bicarbonate

0.40

Butter essence

0.08

Sugar

1.80

Tartaric acid

0.30

1.3.4 Critical ingredients A strong flour produced with 30% of hard wheat will give a good, wellsprung cracker texture. The flour used in the sponge must be 10% 11% protein. Strong flour produces a hard cracker. A weaker flour (8.0% 9.0% protein) is usually used for the dough and will give the product a softer bite.

1.3.5 Mixing and fermentation The sponge and dough are usually mixed on vertical spindle mixers. Two or three spindle machines are used with slow mixing speed, 25 rpm. The slow and gentle mixing action incorporates the ingredients well without undue work input at the sponge stage (Figs. 1.4 and 1.5).

FIGURE 1.4 Vertical spindle mixer from Dingson Food Machinery Ltd. Biscuit Baking Technology

1.3 Soda crackers: process for sponge and dough

7

FIGURE 1.5 Vertical spindle mixer from Dingson Food Machinery Ltd.

The sponge is mixed as an “all-in” mix. The yeast should be dispersed in water before feeding to the mixing bowl. The dough is mixed to a temperature of 30 C 35 C, which is the optimum temperature for the action of the yeast. The sponge is fermented for 18 h at a temperature of 30 C 35 C and an RH of approximately 80%. During this time the pH value will change from about 5.8 to 4.0 and the temperature of the sponge will increase (Fig. 1.6).

FIGURE 1.6 Fermentation room.

After the fermentation of the sponge the dough trough is taken back to the mixing room. The additional ingredients for the dough are added, including sodium bicarbonate. Gentle, slow-speed mixing is required until

Biscuit Baking Technology

8

1. The biscuits, cookies and crackers

a homogeneous dough is made. Over-mixing will reduce the spring and give a hard, tough product. After mixing, the dough is returned to the fermentation room for up to 6 h. With the addition of the soda, a large change in the pH occurs and the dough will reach a pH of over 7.0.

1.3.6 Dough forming The dough is laminated, usually with 4 6 layers at around 4.0 mm thickness. The dough is then gauged with a maximum reduction at each gauge roll unit of 2:1. Excessive reductions of the dough thickness will prevent good lift or spring of the cracker. Typical settings for the gauge roll gaps are: Gauge roll 1:

12 mm

Gauge roll 2:

6 mm

Gauge roll 3:

3 mm

A relaxation conveyor is used to relax the tension in the dough sheet before cutting, as the soda cracker doughs are subject to considerable shrinkage after cutting and during baking. The dough sheet is cut with a “scrap-less” cutter. Each cracker shape is perforated (not cut through), so that the dough sheet remains complete. A small amount of edge scrap is cut off and this is diverted by side scrap wheels to the scrap return system. An additional cross scrap conveyor is used to convey the scrap to the side return conveyor. The dough sheet may be cut through across its width with one revolution of a large diameter cutting roll so that the dough sheet is divided into lengths of approximately 1.0 m in the oven. This allows shrinkage to occur during baking without random breaks in the dough sheet, which may cause problems at the cracker breaker (Fig. 1.7).

FIGURE 1.7 Forming line with sheeter, laminator, gauge rolls and rotary cutter from Skywin Foodstuff Machinery Co.

Biscuit Baking Technology

9

1.3 Soda crackers: process for sponge and dough

1.3.7 Baking

Heat rating / input per square metre of oven band

The baking of soda crackers normally follows the US practice with a direct gas-fired oven and compound-balanced weave oven band with a weight of 20.5 kg/m2. Typically, a CB5 band is used with pre-heat burners to give a high band temperature, over 150 C at the feed end of the oven. Heat is immediately conducted into the bottom of the dough sheet, initiating a fast and strong lift or spring to give the open, flaky texture of the cracker. A considerable amount of water must be evaporated from the soda cracker dough and this is achieved by a high temperature in the middle of the oven (minimum 300 C on a direct gas-fired oven). The fast baking time and high water evaporation require a powerful oven. Soda cracker ovens have a burner capacity of over 30 kWh/m2 of oven band area. The first zone will have a burner capacity of 45 50 kWh/m2 of oven band area (Figs. 1.8 and 1.9).

50000kcal/m2 58 KWhl/m2

40000kcal/m2 47 KWh/m2

30000kcal/m2 35 KWh/m2

20000kcal/m2 23 KWh/m2

preheat 10000kcal/m2 12 KWh/m2

Zone 1 % of oven length 0

Zone 2 10

Zone 4

Zone 3 20

30

Zone 5 40

50

Zone 6 60

Zone 8

Zone 7 70

80

90

100%

Proposed heat ratings for soda cracker oven DGF oven 1.5m x 100m

FIGURE 1.8 Heat rating for soda cracker oven. Temperature profile: 300/300/280/250 C, Baking time: 2.5 3.0 min.

Biscuit Baking Technology

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1. The biscuits, cookies and crackers

FIGURE 1.9 Baker Perkins Direct Gas Fired cracker oven with pre-heat burners.

1.3.8 Oil spray Soda crackers are oil sprayed immediately after baking. The cracker strips are transferred from the oven stripping conveyor to the oil spray machine, where a mist of fine oil is sprayed on the top and bottom of the crackers. Coconut oil or palm kernel oil is used.

1.3.9 Cracker breaking The baked sheet of crackers is broken into lateral strips by a weighted roller positioned over the oven stripping conveyor. The wire-mesh conveyor is supported by rollers before and after the cracker breaker roll. The sheet of crackers is depressed by the breaker roll and breaks into separate strips (Fig. 1.10).

FIGURE 1.10 Cracker breaker roll.

After cooling, the strips must be correctly aligned. Usually, side guide rolls or belts are used to nudge the strips into a central position for breaking. The strips are depressed by breaker wheels aligned with

Biscuit Baking Technology

1.4 Cream crackers: process for laminated crackers

11

the perforations in the cracker sheet and break the strips. The products are normally broken into pairs.

1.4 Cream crackers: process for laminated crackers Refer Fig. 1.11.

FIGURE 1.11

Cream crackers.

1.4.1 Description Cream crackers are usually eaten with butter, cheese and other savoury toppings. They are now widely consumed in South America, Asia and Australasia in addition to England. Malaysian cream crackers, originally made with many laminations on manual dough brakes with filling between the laminations and oil sprayed, are distinctive.

1.4.2 Product specification Dimensions:

68 3 66 mm

Thickness:

6.4 mm

Weight:

7.7 g

Appearance:

Evenly blistered

Colour:

Pale cream or darker biscuit colour with dark blisters

Texture:

Open and flaky, with a crisp bite

Flavour:

Mild flavour

Moisture:

1.5% 2.5%

Biscuit Baking Technology

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1. The biscuits, cookies and crackers

1.4.3 Recipe Refer Table 1.1. TABLE 1.1 Recipe for cream crackers. Flour strong

100.000

Vegetable fat

15.200

Sugar fine

1.400

Yeast fresh

1.400

Malt extract

1.000

Salt

1.150

Sodium bicarbonate

0.060

Water at 32 C

4.400

Water to adjust dough temp.

26.000 150.610

Fat flour dusting Flour strong

100.000

Vegetable fat

34.000

Salt

2.000

1.4.4 Dough mixing on a horizontal high-speed mixer Make a suspension of the yeast and water at 32 C. In the mixer bowl, add the fat, sugar, malt, salt and remaining water. Mix on slow speed for 2 min. Add flour and sodium bicarbonate. Mix on slow speed for 3 min and then on high speed until the dough is clear. 6. Transfer the dough to a tub and prove for 4 h at 32 C and an RH of 70% 80%. Finished dough temperature 29 C 30 C pH 5.8 6.2.

1. 2. 3. 4. 5.

1.4.5 Preparation of the fat/flour for dusting The fat should be in a plastic state at 20 C or less. Care should be taken to avoid oiling when mixing with the flour. Mix for 10 20 min depending on the temperature of the mixing room. After mixing, sieve the mixture and store it at 2 C 3 C for 24 h before use.

1.4.6 Lamination 6 laminations with the fat/flour mixture between the laminations. Add 18 kg of fat/flour dusting to 100 kg of dough. Biscuit Baking Technology

1.4.7 Baking Direct gas-fired oven. Traditionally, cream crackers were baked on an open 5 3 5 mesh oven band. Now a Z47 type wire-mesh band is often used. Baking time:

3.5 4 min

Baking profile:

300/290/270/270/270 C

Final moisture content:

1.5% 2.5%

1.5 Snack crackers Refer Fig. 1.12.

FIGURE 1.12

Snack crackers.

14

1. The biscuits, cookies and crackers

1.5.1 Process for snack crackers Refer Fig. 1.13.

FIGURE 1.13 “Ritz” type crackers.

1.5.2 Description Snack crackers are successful in every market; light and crispy with oil spray.

1.5.3 Product specification Dimensions:

48.0 mm diameter

Thickness:

4.9 mm

Weight:

3.0 g

Appearance:

Evenly blistered

Colour:

Golden

Texture:

Light and crispy

pH:

5.5

Moisture:

1.3% 2.5%

1.5.4 Formulation Flour

100.00

Sugar

8.02

High fructose corn syrup

2.85

Biscuit Baking Technology

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1.5 Snack crackers

Vegetable oil (soya bean)

11.66

Lecithin

0.20

Ammonium bicarbonate

1.84

Sodium bicarbonate

1.08

Acid calcium phosphate

1.08

Salt

0.77

Enzyme

0.01

Water

29.47

1.5.5 Critical ingredients 1. Flour should be weak with a protein content of 8% 9%. 2. Proteolytic enzyme.

1.5.6 Mixing An “all-in” mix on a horizontal mixer. Temperature of about 33 C for enzyme doughs (Fig. 1.14).

FIGURE 1.14 Baker Perkins horizontal high-speed mixer with shaft-less blade, water jacket and dough temperature monitoring.

Biscuit Baking Technology

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1. The biscuits, cookies and crackers

1.5.7 Standing time After mixing, the dough is stood to allow the enzyme to react with the gluten. The standing time is about 2.0 2.5 h at 35 C. The time must be determined carefully depending on the amount of enzyme and the quality of the flour in order to achieve the delicate eating texture of the cracker.

1.5.8 Forming The dough is laminated with 4 laminations, approximately 4 mm thick. No fat/flour filling is used (Fig. 1.15).

FIGURE 1.15 Baker Perkins laminator and cutting machine.

1.5.9 Baking Baking time

5.0 min

Zone temperatures:

220/220/230/230/180 C

Band pre-heated to:

180 C 200 C

High bottom heat in Zones 1 and 2 of the oven is required.

1.5.10 Baking band Z47 type wire-mesh band. Pre-heat is required.

1.6 Semi-sweet biscuits Examples of semi-sweet biscuits are Marie, Petit Buerre, Rich Tea, Arrowroot, Morning Coffee. They are characterised by an even, attractive colour and texture and good volume (Fig. 1.16).

Biscuit Baking Technology

1.6 Semi-sweet biscuits

FIGURE 1.16

Semi-sweet biscuits.

Biscuit Baking Technology

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18

1. The biscuits, cookies and crackers

Doughs for semi-sweet biscuits have the following features: • Doughs have strong, developed gluten which gives an elastic dough, which is sheeted and cut. It often shrinks in the first stage of baking. • Doughs have low sugar and fat. • Doughs have water contents typically of around 12%. • Biscuits are normally baked on a wire-mesh band (except for Marie which is traditionally baked on a steel band). • Humidity in the first part of the baking is important to achieve good volume and a smooth surface sheen. • Biscuits are baked to low moisture contents, around 1.5% 3.0%.

1.6.1 Process for semi-sweet biscuits Refer Fig. 1.17.

FIGURE 1.17 Marie biscuits.

1.6.2 Description Marie is a classic biscuit made throughout Europe and Asia. It has a light, crisp, delicate texture, with pale colour and clear smooth surface.

1.6.3 Product specification Dimensions:

66.0 mm diameter

Thickness:

6.0 mm

Weight:

8.3 g

Appearance:

Smooth surface, clear printing

Colour:

Pale golden

Texture:

Crisp and light

Moisture:

1.5%

Biscuit Baking Technology

19

1.6 Semi-sweet biscuits

Marie biscuits are made with medium protein flour and contain sodium metabisulphite (SMS) to develop a soft, extensible dough. The doughs are mixed on horizontal mixers to a temperature of 40 C 42 C. The dough is sheeted and cut and is traditionally baked on a steel band.

1.6.4 Formulation Flour

100.00

Cornflour

4.41

Maize flour

14.70

Granulated sugar

25.59

Invert syrup 80%

7.94

Shortening

11.03

Lecithin

0.57

Salt

0.88

Soda

0.67

Acid calcium phosphate

0.08

Protease

0.02

SMS 10% solution

0.02

Ammonium bicarbonate

0.73

Water

26.47

1.6.5 Critical ingredients 1. Flour should not exceed 9.0% protein. Higher protein will result in a hard biscuit. 2. Cornflour and maize flour are used to reduce the total gluten content and make a more tender eating biscuit. 3. SMS will modify the protein to make a soft extensible dough.

1.6.6 Mixing An “all-in-one mix” on a horizontal mixer. Mixing is critical to developing the soft extensible dough. A mixing action which kneads the dough without too much tearing and extruding is ideal. Mixing time on a typical high-speed mixer will be 20 25 min. Marie doughs are mixed until the required temperature is achieved. The dough should reach 40 C 42 C. At this temperature, it should be

Biscuit Baking Technology

20

1. The biscuits, cookies and crackers

well kneaded and of correct consistency for machining. Higher dough temperatures result in unstable doughs. The dough is used straight away without standing and it is important to maintain the temperature.

1.6.7 Forming The dough may be laminated, but doughs made with SMS are usually sheeted without lamination. Dough scrap incorporation is very important and should be very even and consistent. The temperature of the scrap dough should be as close as possible to the temperature of the new dough. Dough sheet reduction should be gentle and should not exceed the ratio of 1.5:1 on the gauge roll units. Typical roll gaps are: Forcing roll gap on sheeter:

18.0 mm

Gauging gap on sheeter:

9.0 mm

First gauge roll

5.7 mm

Second gauge roll

2.5 mm

Final gauge roll

1.1 mm (cutting thickness: 1.3 mm)

The doughs shrink and require good relaxation before cutting. Separate cutting and printing rolls on the rotary cutter are recommended to achieve good, clear printing and docker holes, (piercing of holes in the dough pieces).

1.6.8 Baking Steam may be used at the oven entry to achieve a high humidity. This will improve the surface finish of the biscuit. Baking time:

5.0 6.5 min

Temperatures:

200/220/180 C

Moisture:

Less than 1.5%

1.6.9 Cooling A ratio of cooling to baking time should be at least 1.5:1. This will help to avoid checking (cracking of the biscuits after packaging due to an internal moisture gradient).

Biscuit Baking Technology

1.7 Process for Golden Maria or Dorada

21

1.7 Process for Golden Maria or Dorada 1.7.1 Description A semi-sweet biscuit. It is characterised by an attractive design and golden colour, crisp, slightly hard bite, light, open texture (Fig. 1.18).

FIGURE 1.18

Golden Maria.

1.7.2 Product specification Dimensions:

60.0 mm diameter

Thickness:

6.2 mm

Weight:

7.2 g

Appearance:

Rich, golden colour

Texture:

Light and crispy, slightly hard bite.

Flavour:

Semi-sweet

Moisture:

1.0% 1.5%

1.7.3 Formulation Flour

100.000

Cornflour

3.630

Sugar, powdered

21.500

Shortening

17.400

Glucose

3.300

Invert syrup

1.800

Biscuit Baking Technology

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1. The biscuits, cookies and crackers

Sodium bicarbonate

0.530

Ammonium bicarbonate

0.270

Salt

0.980

Lecithin

1.000

Sodium metabisulfite

0.040

Vanilla flavour

0.045

Condensed milk flavour

0.045

Water

17.950

1.7.4 Mixing The dough may be mixed using the “all-in” process. All ingredients are fed into the mixer bowl and there is a single-stage mix. Ammonium bicarbonate is dispersed in some of the water, before adding it to the mixer bowl. Adequate mixing time is required to dissolve the sugar and to hydrate the flour and produce the extensible dough. In order to achieve good dough consistency and keep the added water level low, it is usual to mix to a set temperature of 40 C, rather than to a set time. The dough should be kept warm and used straight away.

1.7.5 Dough forming The dough should be sheeted. The reduction of the dough sheet thickness should be even and as near as possible to 2:1. Recommended gap settings are: Sheeter

12 mm

Gauge roll 1:

6 mm

Gauge roll 2:

3 mm

Gauge roll 3:

1.5 mm

The dough scrap must be returned by a side scrap conveyor and incorporated at the back of the sheeter on the underside of the dough sheet. A relaxation conveyor is used to relax the tension in the dough sheet before cutting, as the dough is extensible and subject to shrinkage after cutting. This control is important to maintain a good, consistent, even shape for the biscuit.

1.7.6 Baking The first zone must be humid to achieve a good surface sheen to the biscuits.

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1.8 Short doughs: rotary moulded biscuits

23

The biscuits will be baked on a wire-mesh band. Good oven extraction is required in all except the first zone to achieve a final moisture content of 1.0% 1.5%. A low moisture content will avoid “checking.” Baking time: 5.0 5.5 min Baking temperature settings: 200/200/220/220/200/180 C.

1.8 Short doughs: rotary moulded biscuits This is another wide biscuit category with many designs. The doughs are short with higher fat and sugar contents than the crackers and semisweet biscuits. This is the simplest category for the dough pieceforming process (rotary moulding) and so these products are very widely produced, often in very high volumes. The list of typical products would be very extensive and contains many local or regional specialities. They include Malted milk, Glucose, Lincoln, Digestive, Nice, Shortbread, Custard Cream from Britain, Italian frollini, Dutch speculaas, caramelised biscuits, Glucose and Tiger from India, etc. (Fig. 1.19).

FIGURE 1.19

Short dough biscuits.

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1. The biscuits, cookies and crackers

• Doughs have a low water content but more fat and sugar than the semi-sweet biscuits. • High humidity in the first part of the baking process allows the biscuit structure to form. • Relatively slow baking at comparatively low temperatures.

1.8.1 Process for moulded short dough biscuits Refer Fig. 1.20.

FIGURE 1.20 Glucose biscuit.

1.8.2 Description A rotary moulded biscuit derived from “Glucose,” a highly popular biscuit in India. One manufacturer in India, Parle Products, sells approximately 13 billion of their Parle G Glucose biscuit every month. “Tiger” type biscuits are made in very large volumes in India and it was successfully introduced into Malaysia and Indonesia. In Indonesia the Danone biscuit “Biskuat” quickly became one of the biggest selling biscuits. The biscuit is a short, sweet, rotary moulded product, developed from the English “Malted Milk” biscuit. It is cheap, nutritious and satisfying. It is often fortified with vitamins and minerals, particularly calcium and iron.

1.8.3 Product specification Dimensions:

58 3 37 mm

Thickness:

6.7 mm

Weight:

5.2 g

Appearance:

Bold design

Colour:

Golden

Biscuit Baking Technology

1.8 Short doughs: rotary moulded biscuits

Texture:

Short and tender

Flavour:

Sweet

Moisture:

1.2% 1.4%

25

1.8.4 Formulation Flour (weak)

100.00

Powdered sugar

29.50

Palm oil

19.50

Glucose 42DE

2.50

Skimmed milk powder

2.35

Fructose

1.25

Salt

1.10

Lecithin

0.62

Calcium carbonate

0.55

Sodium acid pyrophosphate

0.30

Ammonium bicarbonate

0.58

Sodium bicarbonate

0.49

Vitamin mix

0.11

Flavours

0.21

Water

13.33

1.8.5 Critical ingredients 1. Flour should not exceed 8.0% 9.0% protein. Higher protein will result in a tough biscuit, particularly if it is overmixed. 2. The vitamin mix should be developed to suit the local requirement.

1.8.6 Mixing The mixing process must not develop the gluten in the flour as this will result in a tough biscuit. Mixing is therefore done in two stages. In the first stage, all the ingredients are mixed except the flour and soda. The mixing continues until a consistent, homogenous cream is produced. It is important to keep the temperature of the dough low and chilled water is required for the mixer jacket.

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1. The biscuits, cookies and crackers

For the second stage, the flour and soda are added and mixed for 1 min at slow speed and 1 2 min at high speed. The final dough temperature should be 18 C 22 C.

1.8.7 Standing time The dough will be sticky when discharged from the mixer as the flour has not fully absorbed the water. The dough should be stood in a cool area for 30 min before forming. It will then be less sticky and will release from the rotary moulding roll more easily.

1.8.8 Rotary moulding The dough should be fed very evenly and consistently to the hopper of the rotary moulder, maintaining an even level across the width of the machine during the production. Adjustment will be made to the forcing roll gap, knife position and pressure roll to achieve a good release and good product shape (Fig. 1.21).

FIGURE 1.21 Rotary moulder.

1.8.9 Baking Steam may be used at the oven entry to achieve a high humidity. This will allow the biscuit to expand in the first zone and achieve good volume.

Biscuit Baking Technology

1.8 Short doughs: rotary moulded biscuits

Baking time:

5.0 5.5 min

Temperatures:

180/200/220/200/180 C

Moisture:

Less than 3.0%

27

1.8.10 Cooling Sufficient cooling is required to set the biscuit, which will be soft as it leaves the oven, usually 1:1.5 baking to cooling time.

1.8.11 Process for ginger biscuits Refer Fig. 1.22.

FIGURE 1.22

Ginger biscuits.

1.8.12 Description Crisp crunch biscuits, flavoured with ginger, cinnamon and other spices.

1.8.13 Product specification Dimensions:

58 mm diameter

Thickness:

6.53 mm

Weight:

11.35 g

Colour:

Rich

Flavour:

Ginger and spice

Moisture:

2.5% 3.5%

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1. The biscuits, cookies and crackers

1.8.14 Formulation Flour

100.000

Invert syrup

29.267

Castor sugar

24.370

Sugar, granulated

15.600

Sugar milled

2.152

Fat

23.400

Biscuit crumb

5.380

Ground ginger

2.442

Ammonium bicarbonate

1.291

Sodium bicarbonate

1.237

Salt

0.484

Lecithin

0.269

Water

3.766 209.658

1.8.15 Process for ginger crunch biscuits The crunch recipe is mixed on a vertical spindle mixer with all the water for 4 min, followed by the dough mix for 8 min. The biscuits are rotary moulded. Baking on a direct gas-fired oven with wire-mesh band. Water spray and steam in the first zone of the oven will adjust cracking of the surface. Baking time: 6.0 6.25 min Baking temperatures: 300/320/290/270/210 C.

1.9 Cookies Chocolate chip cookies, butter cookies, two-dough cookies, centrefilled cookies, fig bars, fruit bars, extruded cookies, cookies with many types of inclusion such as nuts, raisins, coconut and chocolate chips. • Soft doughs that are deposited directly onto the oven band. • High fat and sugar recipes. • Long baking times with relatively low baking temperatures.

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1.9 Cookies

29

• All products are baked on steel bands. • High humidity is required in the first oven zones to allow the dough to spread on the oven band (Figs. 1.23 1.25).

FIGURE 1.23

Cookies.

Biscuit Baking Technology

FIGURE 1.24 Filled cookies.

FIGURE 1.25 Danish Butter Cookies.

1.10 Process for a chocolate chip cookie

1.10 Process for a chocolate chip cookie Refer Fig. 1.26.

FIGURE 1.26

Chocolate chip cookie.

1.10.1 Description Deposited cookies with inclusions of chocolate chips or nuts.

1.10.2 Product specification Dimensions:

55 mm diameter

Thickness:

12.0 mm

Weight:

15.0 g

Appearance:

Round, irregular shape with chips visible

Colour:

Golden brown

Texture:

Short

Flavour:

Rich with chocolate or nut flavour

Moisture:

2.5% 3.0%

1.10.3 Formulation Flour

100.00

Shortening

55.98

Granulated sugar

50.05

Brown sugar

0.76

Whole egg powder

1.24

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32

1. The biscuits, cookies and crackers

Vanillin

0.10

Invert syrup

1.24

Salt

0.96

Ammonium bicarbonate

0.29

Sodium bicarbonate

0.67

Chocolate chips

30.00

Water

19.14

1.10.4 Mixing The mixing is in two stages on a horizontal or a vertical mixer. Good dispersion of the fat over the flour particles is important and there must be a good proportion of solid fat. The following ingredients are mixed gently in the first stage: shortening, sugars, water, salt, egg powder, vanilla, invert syrup and ammonium bicarbonate. These ingredients are mixed to dissolve the sugar and achieve a creamy emulsion. The water should be cold and the mix kept as cool as possible. The flour and sodium bicarbonate are added for the second stage. The mixing is continued at low speed for no more than 1 min to obtain a homogenous mixture without hydration of the flour and formation of the gluten. The chocolate chips or nuts are added close to the end of the mix and given enough time to disperse evenly through the dough (Fig. 1.27).

FIGURE 1.27 Horizontal mixer by Apinox Srl type RMNL. This mixer is suitable for soft cookie dough. This image belongs to Apinox Srl Italy. Photo by EFFEPI Foto. Biscuit Baking Technology

1.10 Process for a chocolate chip cookie

33

1.10.5 Forming The dough is fed to the hopper of a wire-cut machine. The dough may be fed from a bowl by gravity. The feed rolls of the depositor operate continuously and will extrude the dough through the dies. As the dough is extruded, it is cut by a horizontally reciprocating wire. The wire-cut dough pieces drop directly onto the baking tray or oven baking band (Figs. 1.28 and 1.29).

FIGURE 1.28

Wire-cut cookies deposited on steel band.

FIGURE 1.29

Dough pieces being cut and deposited onto the oven band.

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1. The biscuits, cookies and crackers

1.10.6 Baking Refer Fig. 1.30.

FIGURE 1.30 Baker Pacific indirect radiant oven with heat recovery system.

Baking time:

7.0 min

Temperatures:

180 C 220 C

Moisture:

2.5% 3.0%

1.10.7 Cooling A ratio of cooling to baking time should be 1:1.5.

1.11 Sandwich biscuits Refer Fig. 1.31.

Biscuit Baking Technology

1.11 Sandwich biscuits

FIGURE 1.31

35

Sandwich biscuits.

1.11.1 Description A wide variety of sandwich biscuits with crackers, semi-sweet, short dough and cookie bases and jam or cream fillings. Both single and dual cream deposits are produced.

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1. The biscuits, cookies and crackers

1.11.2 Recipes for creams Creams are generally mixed on vertical spindle mixers (Fig. 1.32; Tables 1.2 1.4).

FIGURE 1.32 Cream mixer from Dingson Food Machinery. TABLE 1.2 Recipe for chocolate cream. Chocolate cream Icing sugar

100.000

Coconut oil

41.618

Hydrogenated palm kernel oil

22.543

Cocoa powder

12.139

Skimmed milk powder

8.670

Lecithin

0.578 185.548

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1.11 Sandwich biscuits

TABLE 1.3 Recipe for vanilla cream. Vanilla cream Icing sugar

100.000

Coconut oil

40.140

Hydrogenated palm kernel oil

21.751

Full cream milk powder

16.186

Vanillin

0.268

Lecithin

0.086 178.431

TABLE 1.4 Recipe for lemon cream. Lemon cream Icing sugar

50.000

Confectionery fat (coconut)

15.000

Confectionery fat (palm kernel)

23.000

Cornflour

2.500

Malt

0.125

Citric acid

0.190

Lecithin

0.950

Tartrazine yellow colour

0.950

Liquid lemon yellow

0.950

Oil of lemon

0.300

Water

0.625 94.590

1.11.3 Process for sandwich production Continuous automatic sandwiching for single and dual deposits may be made by magazine-fed machines or by full-width cookie capper machines (Figs. 1.33 and 1.34).

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1. The biscuits, cookies and crackers

FIGURE 1.33 EverSmart two-colour sandwiching machine.

FIGURE 1.34 Full-width Cookie Capper from Procys.

1.12 Long shelf life cakes, snack cakes A variety of snack cakes are produced on continuous baking ovens. These include layer cakes, baked in a complete continuous sheet, which is subsequently cooled, slit and cut into individual products, snack cakes baked individually in tins or pans and Korean “pies” which are soft deposited doughs, baked on a steel band (Figs. 1.35 and 1.36).

Biscuit Baking Technology

1.12 Long shelf life cakes, snack cakes

FIGURE 1.35

Korean pies.

FIGURE 1.36

Snack cakes.

Biscuit Baking Technology

39

40

1. The biscuits, cookies and crackers

• Cakes are produced from soft batters with relatively low viscosity. • Layer cakes are baked in complete sheets of batter deposited on steel bands. • Some snack cakes are baked in pans with are carried through the oven on chain tracks. • Korean “pies” are baked on steel bands as deposited cookies.

1.12.1 Process for Jaffa cakes Refer Fig. 1.37.

FIGURE 1.37 Jaffa cake.

1.12.2 Product specification Dimensions:

54 55 mm diameter

Thickness:

14.4 mm

Weight:

11.25 g

Cake weight:

3.9 g

Jam weight:

4.8 5.2 g

Chocolate weight:

2.2 2.4 g

1.12.3 Mixing Premix: Liquid egg, (mixed with the glycerine, colour), water. Add chemicals, sugar and flour. Mix for 1.5 min and then pump to holding tank.

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1.12 Long shelf life cakes, snack cakes

41

Mix and aerate: Feed batter to an aerator-type mixer. Rotor speed approximately 100 rpm and pump speed 45 50 rpm (Fig. 1.38).

FIGURE 1.38

Mondomix Aerator VL from Buhler Group.

1.12.4 Baking The steel band is well greased with flour, oil and lecithin. Baking time: 6.5 8.5 min Temperature: 200/200/200/160 C 175 C Note: these temperatures and baking times may vary considerably depending on the oven specification.

1.12.5 Cooling and jam depositing The cakes are cooled on a conveyor and then aligned before the jam depositor. Jam is fed by gravity through a heat exchanger and deposited at about 55 C. Citric acid is pumped through the jam line before depositing to increase the acid content of the jam to 0.9%. The jam is cooled in a tunnel before the cakes are transferred to the chocolate enrober.

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1. The biscuits, cookies and crackers

1.12.6 Recipes Cake Flour

100.00

Sugar, granulated

89.00

Liquid eggs

72.00

Glucose

6.94

Vegetable oil

2.78

Glycerine

2.78

Baking powder

1.39

Salt

0.56

Water

5.56 281.01

Jam Sucrose

100.00

Glucose syrup

60.00

Pectin

1.60

Sodium citrate

0.50

Citric acid

0.25

Flavour

0.162

Colour

0.010 162.612

Chocolate Supplied in blocks Cocoa liquor

40% 42%

Sugar

47% 48%

Cocoa butter

10% 13%

1.13 Summary We have listed the main product types which can be baked on a continuous baking oven: • crackers • semi-sweet biscuits

Biscuit Baking Technology

References

43

• soft dough biscuits • cookies • snack cakes It will be seen that biscuit baking ovens must meet a wide range of process requirements to produce the structure, texture, volume, appearance, colour and moisture content required by each product. The ability to control heat transfer, baking temperature profile, time and humidity are critical factors in producing good quality products. A fundamental understanding of these factors is the foundation for good biscuit oven design.

References Almond, N., 1989. Biscuits, Cookies and Crackers, Volume 2. Elsevier Science Publishers Ltd. Almond, N., Gordon, M., Reardon, P., Wade, P., 1991. Biscuits, Cookies and Crackers, Volume 3. Elsevier Science Publishers Ltd. Apinox srl. Via Bradolini 21, 31020 Castello Roganzuolo di S. Fior (TV), Italy, www.apinox.it. Baker Pacific. Cambridge CB24 9YZ, United Kingdom, www.bakerpacific.net. Baker Perkins. Industrial Biscuit Baking Equipment. Manor Drive, Paston Parkway, Peterborough PE4 7AP, United Kingdom, www.bakerperkins.com. Baking Business. Sosland Publishing Company, www.bakingbusiness.com. Baking Management. A tropical touch. Soy-based solutions. Penton Media Inc. 2008. Benedict M. University of Houston. How does temperature affect yeast activity? MadSci Network. http://www.madsci.org/posts/archives/jan2001/980908832.Gb.r.html, 2021. Buck, J.S., Walker, C.E., 2015. Sugar and Sucrose Ester Effects on Maize and Wheat Starch. Russell Publishing Ltd. Available from: www.newfoodmagazine.com. Buhler Group. Gupfenstrasse 5, Uswill 9240, Switzerland, www.buhlergroup.com. Dingson Food Machinery Ltd. No. 13 Teng Yun Road, Tanzhou Town, Zhongshan City, Guandgdong Province, 528467, China, www.dsm-mc.com. EverSmart Food Equipment Ltd. Shunde Industrial Park, Foshan City, Guangdong Province, China. www.leaderpackaging.com. Eyre C. AB Enzymes launch targets improved biscuit baking. Bakery and Snacks.com. Decision News Media. 2008. www.abenzymes.com. Finelis. National Institute for Health and Welfare. Wheat Flour Whole Grain. 2003-2010. [email protected]. Flour Specifications. Flour Milling and Bakery Research Association FMBRA, www.emerald.com. Food Resource, Oregon State University. Bread Dough. 2010, www.oregonstate.edu. Food Resource, Oregon State University. Gel. Excerpts from Bender Arnold E. Dictionary of Nutrition and Food Technology, Butterworths, Boston, 1990. Food Resource, Oregon State University. Starch. 2010, www.oregonstate.edu. Ghiasi, K., Hoseney, R.C., Varriano-Marston, 1981. Effects of Flour Components and Dough Ingredients on Starch Gelatinisation. Cereal Chemistry 60 (1), 58 61. Available from: www.cerealsgrains.org. Gurney A. Bakery Fats and Oils. Leading Edge. 2008, 1997 Annapolis Exchange Pkwy, Suite 300, Annapolis, MD21401, USA, www.leading-edge.com.

Biscuit Baking Technology

C H A P T E R

2 Baking process This chapter describes the changes that take place from the dough piece to the biscuit during baking and the factors that influence the baking process and the quality of the end product.

2.1 From the dough piece to the biscuit There are three main changes as all biscuits are baked. They are the development of the biscuit structure and texture, the reduction in the moisture content and the development of the colour and flavour. These changes overlap during the baking process; but, it is useful to note that the formation of the structure and texture of the biscuit will take place in the first third of the oven, the reduction in moisture mainly from the middle of the oven and the development of colour and flavour in the final third of the oven (Fig. 2.1).

FIGURE 2.1 Baking process.

2.1.1 Biscuit structure The following characteristics of the biscuits are important in achieving quality products:

Biscuit Baking Technology DOI: https://doi.org/10.1016/B978-0-323-99923-6.00026-0

45

© 2023 Elsevier Inc. All rights reserved.

46 ’ ’ ’ ’

2. Baking process

Texture open, flaky, short, soft, depending on the product type Density/volume low density gives more volume and a lighter bite Bite/mouth feel crispiness, softness, smoothness and crunchiness Flavour many biscuit flavours and fillings are heat susceptible, and the protection of the flavours and texture of the fillings needs consideration for the baking process. For example, for a variety of soft doughs and cookies, a preference will be for a longer baking time at a lower temperature (Fig. 2.2).

FIGURE 2.2 Wide variety of biscuit textures, densities, bites and flavours.

2.1.2 Moisture content ’

’

’

’

An important factor in baking doughs with high water content, such as crackers. Typical water contents of the doughs: Crackers: 15% 25%, semi-sweet: 10% 15% and short doughs: 2% 6% Low moisture content of the final products (1.5% 3.0%) enhances the keeping qualities of the biscuit. Evenness of the moisture content from the centre to the outside of the biscuit requires penetrative heat and adequate time for baking and cooling to avoid “checking” (cracks in the biscuits after packing).

2.1.3 Colour ’ ’

Consistency of colour with time and across the width of the oven band Some products, such as Marie, require a very even bland colour and others such as cream crackers and some rotary moulded designs require colour contrasts and highlights. These features require different heat transfer and baking systems to enhance the appearance of the product (Fig. 2.3)

FIGURE 2.3 Variety of biscuit colour and contrast.

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2.2 Ingredients

2.2 Ingredients The structure and texture of the biscuit are determined by the ingredients, mixing and forming and the baking process. Here, we introduce briefly the main ingredients and process requirements for the baking of biscuits. Our aim is to indicate the complex chemical and physical changes which take place with temperature and particularly during baking. This will inform how we design and operate the baking oven.

2.2.1 Wheat flour The principle ingredient of biscuits is wheat flour. The grain consists of bran (12%), which is the outer husk, endosperm, which is the white centre (85.5%) and the tiny germ (2.5%). Typical biscuit flour is milled to a yield or extraction of 70% 75%. Wholemeal flour is of 100% extraction, and wheat meal flour is in between these extraction rates, normally around 84% extraction. The flour will contain moisture of between 13% and 15%. Wheat flour is composed of carbohydrates (as starch), protein and fat, together with some fibre, ash and trace minerals and vitamins. The protein is mainly gluten, composed of gliadin and glutenin. The percentage of a protein determines the flour strength. A dough made from strong flour with a high protein content, is extensible and can be machined into a continuous sheet for crackers and hard biscuits. A weak flour with a low protein content produces a soft dough which may be moulded or deposited on the baking band and when baked, gives a short texture (Table 2.1).

TABLE 2.1

Wheat flours: typical specifications.

Property

Soft flour (%)

Medium flour (%)

Strong flour (%)

Protein

8.0

10.3

13.2

Wet gluten

25.0

26.0

31.0

Fat

0.0

1.0

2.4

Carbohydrate

80.0

76.3

66.9

Ash

0.3

0.5

0.5

Water absorption

53.0

58.0

60.0

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2. Baking process

2.2.2 Wheat flours: typical specifications 2.2.2.1 Wheat gluten The formation of the gluten, its strength and elasticity are largely determined by the flour specification, recipe and the mixing and forming processes. Wheat flour contains proteins including gliadin and glutenin. In the presence of water, these proteins combine to form gluten. As the dough is mixed, the protein molecules form long strands of gluten, which have strength and elasticity. The gluten forms an elastic web, which gives the dough strength and allows it to be machined into a thin sheet for crackers and semi-sweet biscuits. Crackers are made with “strong” flour, which has a high protein content, typically 10% 12%. The gluten web is also important in trapping air and gas bubbles formed by yeast fermentation and by leavening agents such as sodium bicarbonate (“soda”) and ammonium bicarbonate (“vol”). This leavening process, combined with the laminating of the dough, gives the characteristic open, flaky texture of crackers during baking. Soft or short biscuits are generally made with low protein flour (7% 9%). A low protein flour makes a dough with a much weaker gluten web. In addition these doughs have higher fat contents. The fat coats the flour particles, and this inhibits the hydration of the proteins and the formation of the gluten web. Shorter mixing times also result in less development of the gluten strands, and hence, the biscuits have a short texture. 2.2.2.2 Starch Starch is the main component of wheat flour. It represents almost all of the carbohydrate content and around 80% of the total energy content of wheat flour. Starch is a polysaccharide (many sugars) made up of glucose units linked together to form long chains. The principle starch molecules in wheat flour are amylose, which typically comprises 28% of the total amount of starch. Amylose molecules contribute to gel formation. Their linear chains of molecules line up together and are able to bond to make a viscous gel. Starch is insoluble in water. However, the starch granules do absorb a limited amount of water in the dough and swell. Above temperatures of 60 C 70 C the swelling is irreversible and gelatinisation begins. The gelatinisation may continue until the starch granules are fully swollen, but it is normal in baked products that only partial gelatinisation occurs. The gelatinisation of the starch contributes to the rigidity and texture of the biscuit. In soft dough products, the high sugar and fat content of the dough inhibits starch gelatinisation. The presence of sugars delays the gelatinisation of the starch, which may be due to the competition for the

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2.2 Ingredients

49

water. The fat, composed of triglycerides and surfactants, also tends to inhibit gelatinisation. With high sugar and fat recipes, the dough has a low gel viscosity and strength and produces short and soft biscuits and cookies. As the starch gel is heated further, dextrinisation occurs. This contributes to the colouring of the biscuit. Dextrinisation is the breakdown of starch into dextrins (disaccharides) giving a brown colouring.

2.2.3 Sugar Common sugar (sucrose) is a carbohydrate derived from sugar cane or sugar beet. It is a disaccharide composed of two monosaccharides, a molecule of glucose joined to a molecule of fructose. Sugar gives sweetness, but it is also important in developing the texture of the biscuit. Dissolved sugar tends to inhibit starch gelatinisation and gluten formation and creates a biscuit with a more tender texture. Undissolved sugar crystals give a crunchy, crisp texture. Sugar crystals, which melt during baking, cool to a non-crystalline glass-like state, give a crispy, crunchy texture, particularly on sugar-topped biscuits. Dry sucrose melts at 160 C 186 C. Biscuits with sugar toppings which are melted to a smooth, shiny surface require high-intensity flash heat at the end of the oven to fully melt the sugar. Invert sugar syrup is a mixture of glucose and fructose. The sucrose is split into its component monosaccharides by hydrolysis. The sucrose in solution is heated with a small quantity of acid such as citric acid. After inversion, the solution is neutralised by the addition of soda. The invert syrup is sweeter than sugar, and it contributes to a moist, tender texture in the biscuit.

2.2.4 Leavening agents 2.2.4.1 Yeast Yeast is normally used in the production of cream crackers. The yeast is most active at temperatures of 30 C 35 C during dough fermentation. At temperatures above 40 C, the yeast activity stops and it is therefore inactive during the baking process. 2.2.4.2 Sodium bicarbonate (“soda”) Soda is readily soluble, and it reacts with acidulants, typically citric acid, in the dough in the presence of water, producing carbon dioxide and decomposing to salt and water. The speed of the reaction may be controlled by the type of acidulant used. The leavening of the dough takes place during mixing and fermentation of the dough.

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2. Baking process

2.2.4.3 Ammonium bicarbonate (“vol”) This leavening agent decomposes completely when heated, producing carbon dioxide, ammonia and water. The reaction is rapid at around 60 C, and therefore, the expansion of the dough takes place during the initial stages of baking.

2.2.5 Fats Fats are a vitally important ingredient in achieving the texture, mouth feel and bite of the biscuit. Crackers and hard biscuits have relatively low percentages of fat in the recipes, whereas soft cookies have high amounts of fat. Recipes with high fat contents require little water for producing a cohesive dough and produce soft, short doughs. During mixing, the fat coats the flour particles and this inhibits hydration and interrupts the formation of the gluten. Fats also tend to inhibit the leavening action of the carbon dioxide diffusion in the dough during baking, and this produces a softer, finer texture. Where both fat and sugar amounts in the recipe are high, they combine to make a soft, syrupy and chewy texture. Typical blended vegetable dough fats are solid at ambient temperature and melt over a wide temperature range. Vegetable shortenings are based on hydrogenated oils from the palm (HPKO), coconut and soya bean oil. Most fats used in biscuit making melt below blood temperature (36.9 C), and this avoids a waxy mouth feel. Fats are specified with a Solid Fat Index (SFI), which indicates the percentage of solid fat present in the total fat. A typical dough fat has an SFI of around 18 at 25 C and 12 at 30 C. In baking the main concern with high fat recipes will be the spread of soft cookies on the steel baking band, which is mainly due to the melting of the fat. This occurs very quickly as the dough pieces enter the oven and the temperature of the dough pieces increases above 35 C. Note: For additional information on ingredients for biscuits, refer to Appendix 1.

2.3 Baking process 2.3.1 Development of the biscuit structure and texture It will be seen from this brief consideration of biscuit ingredients that there are complex chemical and physical changes taking place in the biscuit doughs and some of these are heat-dependent. The changes that are temperature-dependent mainly take place during fermentation

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and later during baking. These changes are also highly dependent on the moisture content of the dough and the humidity of the baking chamber. The water in the dough plays a vital role in achieving the biscuit texture and structure. It hydrates the protein allowing the gluten to form and develop and it hydrates the starch granules which swell and gelatinise. The gluten can absorb a large amount of water. As the dough temperature rises, the gluten web swells and becomes strengthened and the structure of gas and air bubbles in the dough forms, causing an increase in the volume of the dough pieces. The swelling of the proteins increases from 30 C to around 50 C. However, denaturation of the proteins takes place at temperatures over 50 C, when the long chains of molecules are broken. As more heat is applied, gluten coagulation occurs above 70 C. At this temperature, some of the moisture is released from the gluten and contributes to the starch hydration and gelatinisation. The air bubbles in the dough are saturated with water, and these expand rapidly as the temperature increases. The increase in volume is 3% at 50 C, up to 50% at 95 C. This expansion creates a significant increase in the volume of the dough piece during baking. The hydrated starch molecules begin to gelatinise at temperatures of 50 C 60 C. In biscuits, this process is partial as there is seldom enough water to fully gelatinise the starch. In short doughs with very little water, the starch gelatinisation is very limited. When the dough pieces have reached temperatures over 70 C, the structure is well formed and becomes stable although starch gelatinisation may continue until the dough reaches a temperature of 95 C. To reach an optimum volume for the biscuit, it is essential that the surface of the dough piece is not dried too quickly, making it rigid and preventing the expansion of the dough piece. The dough piece surface must remain moist and flexible for as long as possible. As the dough pieces, at ambient temperature, enter the oven, some moisture will condense on their surfaces. This not only keeps the surface of the dough pieces moist, but also the condensation releases latent heat, which assists in raising the temperature of the dough. It is important to maintain a humid atmosphere in the first zone(s) of the oven, and in some cases, injecting steam into the baking chamber is also beneficial. The physical and chemical changes noted above which form the texture and structure of the biscuit take place in the first half of the oven. They require not only temperature, but time as well. In some trials, it has been shown that there is a limit to the speed of the temperature increase, which if exceeded will result in a decline in the quality of the biscuit.

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2.3.2 Moisture removal When the gluten and starch have been sufficiently hydrated and the structure of the biscuit is formed, the remaining free water must be evaporated. The water is evaporated from the surface of the dough pieces. This will occur principally at 100 C for pure water, but at higher temperatures (up to 130 C) when the water is held in solution, for example, in a sugar solution. At temperatures over 100 C, the application of heat will always result in moisture loss from the surface of the dough pieces, even in an oven atmosphere which is saturated with water vapour. This loss of moisture from the dough piece is dependent on the temperature, method of heat transfer and the humidity of the oven (Table 2.2). TABLE 2.2 Approximate guide to the moisture removal for the main biscuit categories. Moisture loss Ingredient

Cream cracker

Soda cracker

Snack cracker

Marie

Rotary moulded

Cookie

Flour

100.0

100.0

100.0

100.0

100.0

100.0

Sugar

1.8

0.0

6.0

21.4

25.0

50.8

Syrup

0.0

0.0

5.0

4.8

7.5

1.2

Fat

7.5

10.0

12.0

21.4

32.1

56.0

Leavening

0.9

0.8

2.0

1.3

0.5

1.0

Other

0.7

3.0

2.2

1.3

2.0

2.3

Water

31.0

32.0

20.0

20.0

9.0

19.1

Total

141.9

145.8

147.2

170.2

176.1

230.4

Total moisture

46.0

47.0

36.0

36.0

25.5

35.1

Dry weight

95.9

98.8

111.2

134.2

150.6

195.3

Final moisture (%)

2.5

2.5

2.5

3.0

3.0

3.0

Yield

98.4

101.3

114.0

138.4

155.2

201.3

Moisture to be removed per kg of biscuits baked (kg)

0.31

0.30

0.23

0.19

0.13

0.14

Cracker doughs have a large quantity of added water, typically around 15% 22% of the total recipe. The final product will have a moisture content of around 2.5%, and this will require the vaporisation of 200 300 g of water for every kilogram of baked cracker. The vaporisation of this water

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requires heat transfer (the latent heat of evaporation), which is 539 kcal/kg of water. As an example, the latent heat of evaporation required for baking 1200 kg/h of snack crackers will be around 150,000 kcal/h. This is clearly a significant energy requirement for cracker baking. It is, however, of much less significance for the baking of soft doughs and cookies. The equivalent energy requirement to provide the latent heat of evaporation for a soft dough biscuit would be approximately 84,000 kcal/h. After baking, the biscuits are transferred over a stripping conveyor to a set of cooling conveyors. The biscuits are allowed to cool to approximately ambient temperature before packaging. An important part of this process is allowing the moisture content in the products to reach an even balance between moisture in the centre of the product and the outer layer. If this moisture gradient is too high, the products will be subject to “checking,” cracks and breakage after packaging (Fig. 2.4).

FIGURE 2.4 Cooling conveyor from Ariete Brazil.

2.3.3 Colour There are several chemical and physical changes which contribute to the colouring of the biscuit surface. After the moisture has been mainly evaporated from the dough pieces, the temperature of the surface rises quickly and the colour will change from around 150 C. There are three processes which contribute to the browning of the biscuits. Caramelisation is a non-enzymatic browning reaction, which is caused by the breakdown of sugars at high temperatures. The caramelisation of different sugars occurs at different temperatures: fructose at 110 C, glucose 160 C and sucrose at 160 C. Caramelisation results in both colour and flavour development. A second browning process, dextrinisation is the breaking down of starch molecules by heating. This produces pyrodextrins which are brown

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in colour and have a distinctive flavour. Dextrinisation of the starch occurs at temperatures of 100 C 200 C. The third browning process is known as the Maillard reaction. This is a complex chemistry in which many compounds are formed at high temperatures by the reaction of reducing sugars and amino acids. Since milk has a high content of proteins and amino acids, the Maillard reaction will also contribute to the colour of biscuits which have been brushed with milk before baking, giving a darker, rich brown colour. These browning processes all require high temperatures and occur when the biscuit surface is already dry. The colouring takes place during the final stage of the baking process.

2.3.4 Summary We have seen that there are many complex physical and chemical changes from the dough piece to the biscuit during baking. These changes are mainly temperature- and time-dependent and occur at different stages during baking. They may overlap and interact (Fig. 2.5).

175

Temperature of dough pieces Colouring: Dextrinisation of starch: Caramelisation of sugars Maillard reaction

150

Evaporation of water from surface of dough pieces

Temperature of dough pieces °C

125

Evaporation of water from surface of dough pieces

100 Rapid expansion of water vapour: volume increase Gelatinisation of starch complete

75

Ammonium bicarbonate active: rapid production of CO2

50

25

Gelatinisation of starch begins Yeast activity stops Fats melt Proteins swell

Baking process / time

FIGURE 2.5 Mowbray.

Changes due to the temperature of the dough pieces. Source: After W.

It is important to note that the structure and texture of the biscuit are formed in the first third to half of the oven zones, that the moisture removal is in the middle zones and the colour and flavour development occur at the final stage of baking. The oven design should therefore provide a rapid heat transfer at the start of the bake and maintain a flexible,

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moist outer skin of the dough piece to allow expansion and lift. In the middle of the oven, the moisture should be removed efficiently from the dough pieces and then extracted from the baking chamber. In the final zone(s), the surface of the biscuit will be dry and it will colour. Good lateral heat transfer control is required to maintain an even colour and final moisture content of the baked biscuits. The specification of the baking system should be based primarily on the product(s) to be made and their requirements in terms of structure, texture, density, bite, flavour and colour, a very bland even colour or contrasted background colour with highlights. The characteristics of the biscuits will determine the type of heat transfer (radiation, conduction and convection) which is appropriate at each stage of the baking process. This will define the oven specification, the appropriate heat ratings and the zone lengths. The diagram below shows the heat ratings (heat energy input per m2 of the oven band) for several multi-purpose biscuit ovens (Fig. 2.6).

FIGURE 2.6 Heat ratings for multi-purpose ovens.

References Ayre, C., 2008. AB Enzymes Targets Improved Biscuit Baking. Decision News Media, http://www.bakeryandsnacks.com . Article . 2008/02/14 2021. Bender, A.E., 1990. Dictionary of Nutrition and Food Technology. Butterworths, Boston. Available from: http://www.onlinelibrary.wiley.com, 2021. Benedik, M., 2001. How does temperature affect yeast activity. http://www.madsci.org 2021. Buck, J.S., & Walker, C.E., 2021. Sugar and Sucrose Ester Effects. University of Nebraska, Kansas State University. http://www.onlinelibrary.wiley.com.

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Davidson, A., 2002. The Penguin Companion to Food. http://www.abebooks.co.uk 2021. DTKFCPL, 2003. Examining the Role of Fats in Bakery: http://www.drtkfoods.com 2021. Finelli, 2021. Wheat flour whole grain. http://[email protected]. Food Info, 2021. Caramelisation. http://www.food-info.net/uk/colour/caramel.htm. Food-Info, 2021. Wageningen University: Caramelisation: http://www.food-info.net. Food-Info, 2021. Wageningen University: Maillard Reaction: http://www.food-info.net. Gelatinisation, 2021. American Association of Cereal Chemists. 1982. http://www.cerealsgrains.org. Ghiasi, K., et al., 2021. Effects of Flour Components and Dough Ingredients on Starch http://www.cerealsgrains.org. Gurney, A., 2008. Bakery Fats and Oils. Leading Edge. Johnson, J.M., et al., 2021. http://www.people.oregonstate.edu . foodresource . Starch. Oregon State University. Lansbergen, G., 2021. Fats for Foods Consultants. Fat specifications. http://www.fatsforfoods.com. 2002. Lowe, B., 2021a. The Boiling Point of Water and Solutions. StasoSpere. 2007 2009. http:// www.onlinelibrary.wiley.com. Lowe, B., 2009. The Chemical and Physical Standpoint. StasoSphere. http://www.onlinelibrary.wiley.com 2021b. Manley, D., 1996. Technology of Biscuits, Crackers and Cookies. Woodhead Publishing Ltd. Manley, D., 1998a. Biscuit Doughs. Woodhead Publishing Ltd. Manley, D., 1998b. Ingredients. Woodhead Publishing Ltd. Manley, D., 2001. Biscuit, Cracker and Cookie Recipes for the Food Industry. Woodhead Publishing Ltd. McCance, R.A., et al., 1945. The Chemical Composition of Wheat and Rye and of Flours Derived Therefrom. Department of Medicine, Cambridge. Available from: http:// www.portlandpress.com, 2021. Moodie, P., 2001. Traditional Baking Enzymes Proteases. Enzyme Development Corporation, American Institute of Baking. http://www.enzymedevelopment.com 2021. Penton Media Inc. A tropical touch, Soya-based solutions. Prezi, 2021. Dextrinisation. http://www.prezi.com. Robins, B.A., 1954. Formula, dough mixing method. Review of Literature. Oregon State University. Sumnu, G., et al., 1999. Effects of Sugar, Protein and Water Content. European Food Research Technology. Springer-Verlag. Available from: http://www.link.springer.com, 2021. Wheat flour specifications, 2021. http://www.bakerpedia.com. Yeast Fermentation in Baked Goods, 2021. http://www.ifst.org.

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3 Baking profiles 3.1 Crackers 3.1.1 Structure The crackers require an open, flaky structure and light crispy texture. This requires a high heat input in the first one-third of the oven. The heat input is provided by radiation from the direct gas-fired oven zones and conduction from the pre-heated compound balanced weave band (Fig. 3.1).

FIGURE 3.1 Soda and saltine crackers.

The first zones have minimum extraction and no convection. Humidity is an important parameter, and the initial temperature rise of the dough pieces is faster with a moist atmosphere. In a direct gas-fired oven, about 30% of the humidity is from the products of combustion. Steam may also be applied at the oven feed end. The surface of the dough pieces must remain flexible to lift and achieve the required volume and thickness of the cracker (Figs. 3.2 3.4).

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FIGURE 3.2 Baker Perkins direct gas-fired oven with pre-heat burners.

FIGURE 3.3 Direct gas-fired oven with multi-fibre burners.

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FIGURE 3.4 Rexnord Cambridge Engineered Solutions CB5 compound balanced weave band.

3.1.2 Moisture content Cracker doughs have a high percentage of water, approximately 20% 25% of the total dough weight. The moisture is removed in the middle and final zones of the oven. The moisture content will be reduced to 1.5% 2.5% of the product weight. This requires the evaporation of approximately 200 g of water for every kilogram of cracker baked. This requires heat transfer of 108 kcal for the latent heat of vaporisation per 1 kg of baked cracker or 108,000 kcal (125 kWh) for every 1 tonne of baked cracker. 3.1.2.1 Latent heat of evaporation: 539 kcal/kg The evaporation of the water requires a high heat input. The cracker oven will have a high heat rating based on the radiant heat transfer and conduction from the pre-heated oven band. Heat transfer in the middle and final zones of the oven can be enhanced by the turbulence system.

3.1.3 Colour Radiant baking in the final oven zones is essential to achieving colour contrast for the crackers to show darker blisters and a pale background (Fig. 3.5).

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FIGURE 3.5 Soda crackers.

3.1.4 Oven specification Direct gas-fired oven with turbulence and pre-heated compound balanced weave band. Typical baking time:

2.5 min

Oven set temperatures:

300/300/280/250 C

3.1.5 Baking profile Baking profile for soda crackers is shown in Fig. 3.6.

Baking temperatures

300°C

250°C

200°C

150°C Set temperatures 300°C 300°C 280°C

280°C

250°C

280°C

250°C

250°C

100°C

% of oven length 0

10

20

30

40

50

60

Proposed baking profile for soda cracker oven DGF oven 1.5m x 100m

FIGURE 3.6 Baking profile for soda crackers.

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80

90

100%

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61

3.2 Snack crackers

FIGURE 3.7 Snack crackers.

3.2.1 Structure There are a variety of textures (Fig. 3.7), from the open layered crackers, even textures such as ‘TUC’ type and hollow products such as fishes (Figs. 3.8 3.10).

FIGURE 3.8 ‘Ritz’ type

FIGURE 3.9 ‘TUC’ type

laminated.

sheeted and cut.

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FIGURE 3.10 Fishes type

3. Baking profiles

rotary cut without docker pins.

3.2.2 Baking process The first zones have minimum extraction and no convection. The surface of the dough pieces must remain flexible to lift and achieve the required volume and thickness of the cracker. Most snack crackers are baked on Z47 type open wire-mesh oven bands. Fishes may be baked on a compound balanced weave band (Figs. 3.11 and 3.12).

FIGURE 3.11 Baker Pacific direct gas-fired oven for snack crackers.

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FIGURE 3.12

63

Agrati La Bridoire Z47 wire-mesh oven band.

3.2.3 Moisture content Snack cracker doughs have a high percentage of water, approximately 10% 20% of the total dough weight. The moisture is removed in the middle and final zones of the oven. Water in the dough

Final moisture content

Ritz type:

15% 20%

1.3% 2.0%

TUC type:

10% 13%

1.5%

Fishes type:

18%

2.0% 3.0%

The evaporation of the water requires a high heat input. The cracker oven will have a high heat rating based on the radiant heat transfer. Heat transfer in the middle and final zones of the oven can be enhanced by the turbulence system. Time and infrared radiation, which penetrate the dough pieces, are important to achieve the most even moisture content from centre to outside of the cracker.

3.2.4 Colour The snack crackers generally have a very even colour achieved by radiant heat with turbulence.

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3.2.5 Baking times and temperatures Ritz type: Baking time

3.5 4.0 min

Oven set temperatures:

220/230/240/240/220 C

TUC type: Baking time:

4.5 5.0 min

Oven set temperatures:

280/270/230/200/200/150 C

3.2.6 Baking profile Baking profile for Ritz-type cracker is shown in Fig. 3.13.

FIGURE 3.13 Baking profile for Ritz-type cracker.

3.3 Semi-sweet biscuits 3.3.1 Structure Examples of semi-sweet biscuits are Marie, Petit Buerre, Rich Tea, Arrowroot and Breakfast biscuits. They are characterised by an even, attractive colour with a smooth surface sheen, light texture and good volume. The surface of the dough pieces must remain flexible to lift and achieve the required volume, texture and thickness of the biscuit (Fig. 3.14).

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FIGURE 3.14

65

Semi-sweet biscuits.

The dough sheet is cut at 1.3 mm. A good Marie biscuit will attain a thickness of 5.6 6.0 mm (Figs. 3.15 3.17).

FIGURE 3.15 Baker Pacific direct gas-fired/indirect radiant oven.

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FIGURE 3.16 Steam injection at the oven feed end.

FIGURE 3.17

Steinhaus F4102 wire-mesh oven band.

Doughs for semi-sweet biscuits have the following features: • Doughs have strong, developed gluten which gives an elastic dough, which is sheeted and cut. It often shrinks in the first stage of baking. • Doughs have relatively low sugar and fat. • Biscuits are normally baked on a wire-mesh band (except for Marie which is traditionally baked on a steel band). • Humidity in the first part of the baking is important to achieve good volume and a smooth surface sheen. The initial temperature rise is faster with a moist atmosphere than in a dry oven. • Biscuits are baked to a low moisture content, around 1.5% 2.0%.

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3.3.2 Moisture content Doughs have water contents typically of around 12%. The biscuits will have a final moisture content of 1.5% 2.0%.

3.3.3 Colour Steam application at the oven feed end assists in developing an attractive sheen to the surface of the biscuits. The very even colour required is assisted by turbulence in the final zones.

3.3.4 Oven specification Hybrid direct gas-fired/indirect radiant oven with turbulence; wiremesh band. Baking time:

5.0 6.5 min

Oven set temperatures:

200/220/220/180 C

3.3.5 Baking profile Baking profile for Marie biscuits is shown in Fig. 3.18.

FIGURE 3.18

Baking profile for Marie biscuits.

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3.4 Short dough biscuits 3.4.1 Structure This is a wide biscuit category with many designs. The doughs are short with higher fat and sugar content than semi-sweet biscuits. This is the simplest category for the dough piece-forming process (rotary moulding), and so these products are very widely produced, often in high volumes (Fig. 3.19).

FIGURE 3.19 Short dough biscuits.

• Very wide variety of shapes and designs. • Doughs have a low water content, but more fat and sugar than the semi-sweet biscuits. • High humidity in the first part of the baking process allows the biscuit structure to form. • Relatively slow baking at comparatively low temperatures.

3.4.2 Moisture content Doughs have water contents typically of around 4.0% 5.0%. The biscuits will have a final moisture content of less than 3.0%.

3.4.3 Colour Infrared radiant heating is required to provide colour contrasts and highlight the design with darker areas against a paler background.

3.4.4 Oven specification Indirect Radiant Oven with turbulence and heat recovery system; open wire-mesh band (Fig. 3.20).

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3.4 Short dough biscuits

FIGURE 3.20

Baker Pacific Indirect Radiant oven.

Baking time:

5.0 6.0 min

Oven set temperatures:

180/200/220/200/180 C

3.4.5 Baking profile Baking profile for short dough biscuits is shown in Fig. 3.21.

300°C

Baking temperatures

250°C

200°C

150°C

Set temperatures 190°C 220°C 225°C

225°C

220°C

225°C

200°C

180°C

100°C

% of oven length 0

10

20

30

40

50

60

Proposed baking profile for a short biscuit Indirect Radiant Oven 1.25m x 100m

FIGURE 3.21

Baking profile for short dough biscuits.

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90

100%

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3. Baking profiles

3.5 Cookies 3.5.1 Structure Chocolate chip cookies, butter cookies, two-dough cookies, centrefilled cookies, fig bars, fruit bars, extruded cookies and cookies with many types of inclusion such as nuts, raisins, coconut and chocolate chips (Fig. 3.22).

FIGURE 3.22 Cookies. ’ ’ ’ ’ ’

Very soft doughs which are deposited directly onto the oven band. High fat and sugar recipes. Long baking times with relatively low baking temperatures. All products are baked on steel bands. High humidity is required in the first oven zones to allow the dough to spread on the oven band.

3.5.2 Moisture content Doughs have water contents typically of around 3.0% 7.0% with an average of 5.2%. The biscuits will have a final moisture content of 2.5% 3.0%.

3.5.3 Colour Infrared radiant heating with turbulence and relatively long baking time provide even colour.

3.5.4 Oven specification Indirect Radiant Oven with turbulence and heat recovery system; steel band (Figs. 3.23 3.25).

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3.5 Cookies

FIGURE 3.23

Baker Pacific Indirect Radiant oven with Heat Recovery System.

FIGURE 3.24 Heat recovery zone.

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FIGURE 3.25 Steel band.

Typical baking time:

7.0 min

Oven set temperatures:

180/200/220/200/180 C

3.5.5 Baking profile Baking profile for cookies is shown in Fig. 3.26.

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References

FIGURE 3.26

73

Baking profile for cookies.

References Agrati La Bridoire, 2020. SARL. 640 Rte du Lac, 73520, France. http://www.agrati.com. Ashworth Bros Inc., 2020. 450 Armour Dale, Winchester, VA 22601, USA. http://www. ashworth.com. Baker Pacific Ltd, 2021. Manor Drive, Paston Parkway, Peterborough PE4 7AP, United Kingdom. http://www.bakerpacific.net. Engineering Tool Box, 2021. http://www.engineeringtoolbox.com. IPCO, 2021. Sweden AB, 2453-B Va¨stra Verken, 81181 Sandviken–Sweden. http://www. ipco.com. Rexnord Cambridge Engineered Solutions, 2020. 105 Goodwill Road, Cambridge, MD21613, USA. http://www.cambridge-es.com. Steinhaus Gmbh, 2020. Platanenallee 46, 45478 Mu¨lheim an der Ruhr, Germany. http:// www.steinhaus-gmbh.de.

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4 Biscuit design and output This chapter introduces various factors of biscuit design and forming of the dough pieces which influence the baking operation.

4.1 Cutter and moulding roll layouts The design of the cutting rolls and moulding rolls and dies for deposited cookies determine the pattern of dough pieces on the oven band. The cutting and moulding rolls are designed to give the maximum number of dough pieces per square metre of oven band and provide even spacing. In the design of dies for cookies, allowance is made for the spread of the dough on the oven band during baking. Normally the rolls are designed to provide a separation of about 8 10 mm between the edges of the biscuits on the oven band. The distance between dough pieces from a cutting machine must also allow a sufficiently strong scrap dough lattice to be lifted without breaking after the cutter. Rectangular biscuits are baked with the short edge leading, which aids control during cooling, stacking and feeding to the packaging machines. Round biscuits may be ‘nested’ to gain the maximum loading on the oven band (Figs. 4.1 and 4.2).

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FIGURE 4.1 Cutting and embossing rolls.

FIGURE 4.2 Rotary moulding roll engraving.

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The technical drawings for the mould or cutting rolls will provide detail: • • • • •

Dimensions of the product before baking Volume of the product to calculate weight Design of the cavity of the mould or cutter with docker pins Material of the mould or cutter Layout drawing for the rolls showing the distance between products, rows in line or staggered • Construction drawing of the roll

4.2 Scrap and scrapless designs Semi-sweet and cracker biscuits are produced from a continuous sheet of dough. The biscuit shape is cut, printed and perforated before being deposited (panned) onto the oven band. Most products are cut into separate individual dough pieces before baking. The scrap dough around the dough pieces is recovered after the dough pieces are cut and returned to the sheeting machine at the start of the forming process. Some products, notably soda crackers and some snack crackers, are baked in a continuous sheet. The dough sheet is perforated so that it can be easily and automatically broken after baking into individual biscuits. When products are presented to the oven as a large sheet, there are several considerations. The edges of the sheet at each side will pick up more heat from the edges of the oven band, which are not covered by the dough. The edge biscuits will therefore have more colour, and this can be excessive. Oven band screens are used on some oven designs which deflect hot air away from the band edges. These are adjustable and will reduce the movement of hot air at the band edge and hence reduce the colour of the edge biscuits. In severe cases the biscuits may be baked with edge scrap dough which is removed after baking. Cracker dough sheets usually shrink during baking, and this can cause random breaks at the perforations on the edge of individual biscuits. These random breaks cause problems after baking at the automatic breakers as the biscuit sheets are presented irregularly. It is therefore worthwhile to reduce the size of the dough sheets, and these may be cut through at approximately 1.0 m length by a large diameter cutting roll (approximately 320 mm in diameter). Alternatively the crackers may be cut and baked in strips (Figs. 4.3 4.5).

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FIGURE 4.3 Soda crackers cut into strips.

FIGURE 4.4 Soda crackers baked on a sheet.

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FIGURE 4.5 ‘Scrap-less’ cutting roll with docker pins from Errebi Technology.

4.3 Semi-sweet biscuits Most semi-sweet biscuits are sheeted and cut into individual dough pieces with suitable spacing for baking (Fig. 4.6).

FIGURE 4.6

Rotary cutting for semi-sweet biscuits.

The applications for the designs of semi-sweet biscuits have been greatly expanded to provide products with 3D effects and perforations. This has been made possible with a design study for angles and cutting depths at different levels by Errebi Technology. This allows a

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great variety of shapes for semi-sweet biscuits for single products or sandwiches. This technology also allows the production of semi-sweet biscuits with holes without the recovery of scraps. A complete full-width dough sheet with a scrapless layout can be produced including for products with inclusions. The sandwich designs can be made with holes to partially expose the filling to give an attractive appearance (Fig. 4.7).

FIGURE 4.7 Semi-sweet hard dough biscuit designs from Errebi Technology Spa.

4.4 Short dough biscuits and cookies Moulded and deposited cookies are formed and baked individually. Some extruded products, such as filled bars, may be baked in continuous ‘ropes’ and cut after baking. Layer cakes are baked in continuous sheets and slit and cut after baking (Figs. 4.8 and 4.9).

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FIGURE 4.8 Filled products may be extruded and cut after baking.

FIGURE 4.9 Layer cake baked on a steel band.

4.5 Docker pins During baking, biscuits and crackers expand and lift to form a light open texture. During this process, the rapid expansion of water vapour in the dough pieces occurs and the vapour needs to be released. This is accomplished by a series of holes in the biscuit design, called docker holes. The docker holes are placed in the design to release the vapour evenly and maintain a flat surface and even thickness of the biscuit. This accurate control of flatness and thickness is essential to the successful automatic packaging of the biscuits. The design of the docker pins is critical, for example, the profile, radius and shape of the head. These depend on the product, cut or moulded and the material of the moulds or cutters (Figs. 4.10 4.12).

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FIGURE 4.10 Biscuits with docker holes.

FIGURE 4.11 Maria biscuit.

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FIGURE 4.12 Cutter design for Maria showing the docker pin arrangement. Note the dough piece is cut as an oval shape to compensate for shrinkage during baking. Drawing and design by ErreBi Technology Spa.

4.6 Oven band loadings The band loading (weight of dough pieces on the oven band) will vary considerably depending on the biscuit design, layout, biscuit weight and water content in the dough. The loading and type of oven band will influence the design of the oven band supports, drive and tracking system. The weight of the oven band will also determine the supports. Wiremesh bands vary from 5.0 kg/m2 up to 22.0 kg/m2 for Z47 type and compound balanced weave bands.

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Biscuit

Dimensions mm

Weight gm

Oven band loading kg/m2

Biscuit weight kg/m2

‘Ritz’ type cracker

48 diametre

3.0

1.34

1.04

Vegetable crackers

48 3 48

3.75

1.50

1.12

Soda crackers

91 3 44

6.25

2.04

1.42

Marie

66 diametre

8.3

1.93

1.57

Glucose/‘Tiger’

58 3 37

5.2

2.04

1.80

Butter cookie

46 3 29

6.0

3.23

2.86

Wire cut cookie

50 diametre

6.5

2.20

2.00

Choc chip cookies

55 diametre

15

4.50

4.00

Note: approximate figures based on typical recipes.

4.7 Oven size and output Usually the oven is the critical item in determining the capacity of a complete biscuit line. Other considerations are mixing capacity, forming machine speeds, cooling and packing capacity, and these are usually specified to suit the required oven output. The output of biscuits from an oven is determined by the baking time and the oven size. To determine the output from an oven, we calculate the number of biscuits across the width of the oven band and multiply this by the number of biscuits contained in the length of the oven. This gives the total number of biscuits contained on the oven band during baking. We divide this by the baking time in minutes, and this gives the total number of biscuits which will be baked in 1 min. The output is usually expressed as the number of biscuits baked in 1 min, or in kilogram of biscuits baked in 1 h. For example, we can calculate the output for a typical rectangular moulded biscuit based on the following data: Oven size (bandwidth): 1200 mm Oven size (baking chamber length): 60.0 m Biscuit size: 57 3 35 mm Biscuit weight: 4.5 g Baking time: 3.8 min

4.7.1 Output calculation Biscuits across the oven band: 27 (allow 43 mm pitch) Biscuits in the length of the oven: 923 (allow 65 mm pitch) Total biscuits contained on the oven band: 27 3 923 5 24,921

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Biscuits baked per minute: 24,921/3.8 5 6558 Oven output in kg/h: 6558 3 60 3 4.5/1000 5 1770 kg/h

4.8 Summary 1. The cutting and moulding rolls are designed to provide the optimum oven band loading. 2. Consideration is given to the spacing between dough pieces on the band, the spread of cookies during baking and the orientation for the cooling and packing. 3. Some products such as soda crackers and snack crackers can be baked in a continuous sheet. Care must be taken to avoid excessive edge colour and irregular breaking of the dough sheet in the oven. 4. Docker pins are used to create holes in the dough pieces to allow the escape of water vapour and control the surface form of the biscuit, giving a regular flat surface with even blisters on crackers and hard sweet biscuits. 5. Biscuit output from the production line is usually determined by the size of the oven. The output is calculated from the biscuit size and weight, oven loading, oven bandwidth, length of the baking chamber and the baking time.

Further reading Baker Perkins Ltd, 2021. Manor Drive, Paston Parkway, Peterborough, PE4 7AP United Kingdom. www.bakerperkins.com. Errebi Technology Spa, 2021. Via Ca` Mignola Nuova, 1290, 45021 Badia Polesine RO, Italy. http://www.errebi.net. Shanghai Kuihong Food Machine, 2021. Chemical Industrial Park, Fengxian, Shanghai. www.kuihong-foodmachine.com Manley, D., 1996. Technology of Biscuits, Crackers and Cookies. Woodhead Publishing Ltd. Manley, D., 2001. Biscuit, Cracker and Cookie Recipes for the Food Industry. Woodhead Publishing Ltd.

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5 Heat transfer In the baking process, heat transfer is by radiation, conduction and convection. The optimum heat transfer mode will vary for different biscuits, cookies and crackers. Each mode of heat transfer is beneficial at different stages of the baking process. So an ideal baking oven will provide the heat energy in the appropriate way at each stage for the particular product. All three heat transfer modes occur during biscuit baking. Radiation is from burners or electric heaters and the baking chamber surfaces in direct-fired ovens. Radiation is primarily from heated ducts or tubes and the baking chamber surfaces in indirect radiant ovens. Conduction is from the oven band to the base of the products. Forced convection is from the movement of hot air impinging on the products. The heat transfer modes differ in importance and effect on each type of product and their application depends on the oven design.

5.1 Radiation All objects above a temperature of absolute zero (in Kelvin) radiate energy to their surroundings. This radiant energy is emitted as electromagnetic waves which travel at the speed of light. The waves may travel through a vacuum or other medium. When they impact an object (other than a perfect ‘black body’), they are partially absorbed and partially reflected. Good emitters are also good absorbers of thermal radiation (Fig. 5.1).

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FIGURE 5.1 Radiant heating.

5.1.1 Wavelength Electromagnetic waves vary in wavelength from infinitely short to infinitely long. They cover a spectrum from gamma rays (around 10214 m) to radio waves (around 102 m). Visible light is a form of electromagnetic radiation with wavelengths of 0.40
0.71 µm (microns). Infrared (IR) radiation, which is important in baking, has wavelengths above visible light from 0.78 µm to 1.0 mm. Near-infrared (NIR) wavelengths are in the range 0.78
5.0 µm. Far IR wavelengths are from 5.0 µm to 1 mm. Microwave baking uses longer wavelengths, normally around 12 cm (Fig. 5.2).

FIGURE 5.2 Radiant wavelengths and frequencies.

Wavelength

Frequency

Near-infrared

0.78
5 µm

214
400 THz

Far-infrared

50
1000 µm

0.3
20 THz

Microwaves

1000 µm to 30 cm

1,000,000
1000 MHz

Radio waves

30 cm to 10 m

1000
50 MHz

Most radiant energy emitted in a baking oven is within the IR spectrum, and most of the energy emission is spread over a relatively narrow spectrum. The peak wavelength is inversely proportional to temperature. A higher temperature produces a shorter wavelength. The relationship is known as Wien’s Law and is described by the following equation:

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Maximum wavelength 5 C/T where C is a constant equal to 2898 and T is the temperature in Kelvin units (Kelvin units 5 Celsius temperature 1 273.15). If we consider a radiant oven with the hot tubes or ducts at 350 C, the wavelength will be: 2898/(350 1 273.15) 5 4.65 µm. This is a typical wavelength in an indirect radiant oven, and it is in the NIR spectrum. IR radiation has a penetration depth of several millimetre in many food products. This is an important factor in biscuit baking since the radiant heat will fully penetrate the dough pieces to develop the structure and reduce moisture content.

5.1.2 Radiant heat transfer Thermal radiation is transferred from objects of a higher temperature to objects of a lower temperature. The electromagnetic radiation emitted by an object is directly related to its temperature. If the object is a perfect emitter (a black body), the amount of radiation given off is proportional to the fourth power of its temperature as measured in Kelvin units. For objects other than perfect black bodies, the power of radiation Q is also proportional to the object’s emissivity e. The emissivity of the surface has a marked effect upon the radiant heat emitted. A perfect “blackbody” radiator has the maximum emissivity of one. A poor radiator such as polished aluminium may have an emissivity of less than 0.05, that is, less than 5% of a perfect surface. Oxidised steel has an emissivity of 0.79, and this is a typical material for baking chambers. For most food products, the emissivity is equal to the absorptivity. The radiant heat transfer per unit area is described by the StephanBoltzmann law:
Q 5 εσA T14
T24 where ε is the emissivity coefficient of the radiating surface, σ sigma is the constant of proportionality called the Stephan-Boltzmann constant, A is the area of the emitting body in m2 and T14 2 T24 is the difference in temperatures to the power of 4 in Kelvin Since the radiation is proportional to the temperature difference to the power of 4, a small increase in temperature will produce a very large increase in thermal radiation. The amount of radiation increases exponentially with a linear rise in temperature.

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5.1.3 Distance The thermal energy radiated to an object is dependent on the object’s distance from the source of the radiation. The intensity of the thermal radiation received is inversely proportional to the object’s distance from radiating surface (inverse square law). Intensity 5 I=d2 where I is the intensity of radiation at the object’s surface and d is the distance from the radiating surface. For example, if the distance is halved from 20 units to 10, the intensity will be multiplied by 4. At 20 units distance: Intensity 5 100/202 5 0.25 At 10 units distance: Intensity 5 100/102 5 1.00 This is an important factor in the design of an oven. The nearer the radiating surfaces are to the product, the more intense the thermal radiation will be and the more efficient the heat transfer. The design and dimensions of the baking chambers and radiant surfaces critically affect the oven efficiency.

5.1.4 Effect of radiation on the dough pieces When IR energy impacts an object, such as a dough piece, its primary effect is to set molecules in vibration. The temperature of the dough piece is a measure of the average kinetic energy of its molecules, which increases due to the radiation from the oven surfaces in the baking chamber. Objects such as dough pieces will absorb part of the IR energy impacting on them and will reflect part. The energy absorbed penetrates the dough pieces and rapidly heats the centre of the dough pieces as well as the surface. This is an important attribute of radiation. IR radiation has a penetration depth of several millimetre in many foods and will penetrate the dough pieces. This provides heat transfer to create the structure and texture of the biscuits at the first stages of the baking process. IR technology is energy efficient and provides a high heat transfer rate and penetrative homogeneous heating through the product. Heating through convection and conduction from the oven band primarily affects the temperature of the outside surfaces of the products. IR heating penetrates the food. The depth of penetration depends on the water activity and composition of the products. Biscuit doughs absorb IR radiation at wavelengths over 2.5 µm through a change in the vibration of water molecules which causes the temperature increase. This radiation is absorbed by the biscuit ingredients.

Biscuit Baking Technology

5.1 Radiation

Food component

Maximum absorption wavelength (µm)

Water

2.7
5.0

Sugar

2.7
3.7

Proteins

2.83
5.92

Lipids, fats

4.4
5.76

91

These components of biscuits absorb IR radiation at NIR wavelengths. A model of the baking of biscuits in an indirect-fired oven extrapolated to a band oven baking process indicated a heat transfer profile of 45% by radiation, 35% by forced convection and 20% by conduction. Another study of heat and mass transfer in industrial biscuit baking ovens found 69% of heat transfer by radiation, 28% by convection and 3% by conduction. Most studies revealed that radiation was the predominant mode of heat transfer, varying between 50% and 80% (Figs. 5.3 and 5.4).

FIGURE 5.3 Direct gas-fired burners.

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FIGURE 5.4 Radiant tubes in an indirect radiant oven.

5.1.5 Radio-frequency baking Radio-frequency (RF) baking has been used effectively for many years. The RF heaters are separate units located immediately after the conventional ovens. They have been primarily used to avoid checking, particularly for crackers and semi-sweet biscuits. The checking results from stresses caused by the moisture gradient between the centre of the biscuit and the surface. This causes cracking of the product before and after packing. As bandwidths have increased and baking times have become faster, this problem has become more difficult to control. In addition, the increasing use of convection baking, which rapidly dries and colours the surface of the biscuit, while there is moisture in the centre of the biscuit, also exacerbates the problem of checking. RF heaters subject the products to a direct heating process in the form of RF energy. The process is known as dielectric heating. The products pass between electrodes above and below the band. These electrodes are charged positively and negatively, and the polarity is reversed. This causes frictional heating of the water molecules. Most RF heaters used in dielectric heating have frequencies of 27.12 MHz which is reserved for industrial, scientific and medical applications (Figs. 5.5 and 5.6).

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5.1 Radiation

Electrodes

RF Generator Product

FIGURE 5.5 Simple RF heating set-up. RF, radio-frequency. Source: From Koral Associates.

– – – – – – +

+

+

+

+

+

– – – – – –

FIGURE 5.6 Reversal of polarity causes the material to heat. Source: From Koral Associates.

The RF energy is produced by a generator which comprises a power supply, a cooling system and an electronic oscillator. The RF heater is placed immediately after the baking oven. The products are carried on a synthetic band. Usually the products are flat on the band as in the baking oven; however, the RF system works more efficiently if the products are shingle stacked. RF heaters substantially reduce checking and also increase output as the baking time may be reduced by up to 30% (Fig. 5.7).

FIGURE 5.7 A 75 kW Strayfield post-baking dryer in stainless steel. Source: From Koral Associates.

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5.1.6 Near-infrared baking Wavelengths of 1.2
5 µm are particularly effective in baking because they penetrate the steam layer over the products. Trials carried out by Peter Wade at United Biscuits found significant benefits in baking with NIR for a semi-sweet biscuit and a cookie. Quartz tungsten tubes were used emitting a peak wavelength of 1.2 µm. The baking time on a conventional oven with a wire-mesh band was reduced by approximately 50%. In addition the moisture content was more even between the centre and surface of the biscuits. This reduced checking. However, most biscuit manufacturers did not accept the use of quartz tungsten tubes above the product, and there are few applications in the industry. The use of NIR by Heraeus has however been developed for other food applications, for example, germ reduction on bread, browning of meat and cheesecake, caramelising of sugar and the heating of nuts (Fig. 5.8).

FIGURE 5.8 Quartz tungsten tubes from Helios Quartz.

5.1.7 Microwave Trials with microwave baking after forced convection ovens gave similar results to RF heaters. Microwaves vibrate water molecules at 2450 MHz. This drying process from the centre of the product provides a more even moisture content through the product. Checking was reduced in one trial to 5% from 61%, but the thickness and volume of the biscuits were also reduced. The applications of industrial microwave baking of biscuits have been very limited, partly due to the cost of generating the radiation and the safety concerns, but also because the microwave heating requires a synthetic band to carry the products and so it can only be applied as a postbaking process. Microwaves would be reflected by a metal band and cause arcing between the metal band and the baking chamber walls.

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5.2 Conduction Conduction is the transfer of thermal energy between neighbouring molecules within an object or between objects in contact with each other. It transfers energy from an area of higher temperature to an area of lower temperature and acts to equalise the temperature difference. The law of heat conduction is known as Fourier’s law, and this is shown in the equation below. Q 5 2 krT The heat conduction Q is proportional to the thermal conductivity k, multiplied by the negative temperature gradient (difference in the higher and lower temperatures) 2 krT Thermal conductivity k is the property of a material that indicates its ability to conduct heat. The thermal conductivity predicts the power loss in watts through a piece of material. This is important in calculating the optimum insulation required for the oven.

5.2.1 Baking with conduction The conduction of thermal energy to the dough pieces during baking is most relevant to baking on a solid steel band or a compound balanced weave band such as a CB5 type. In these cases, the dough pieces are deposited directly onto a hot oven band, and the heat is conducted rapidly into the base of the dough pieces. Compound balanced weave bands are normally pre-heated to a high temperature, 120 C
150 C. Solid steel bands and CB5 bands have a relatively large heat mass and a large area in contact with the dough pieces. The conduction of heat to the base of the dough piece is optimised and contributes significantly to the total heat transfer. It is ideal for products such as soda crackers requiring high bottom heat to achieve good volume and an open texture. Conduction is also of major importance in the baking of soft cookies and cake on steel bands. The band conducts heat directly into the base of the cookies causing the fats to melt and the cookie dough to flow on the band to its final shape (Figs. 5.9
5.13).

FIGURE 5.9 Conduction.

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FIGURE 5.10 Cookie dough deposited on a steel band.

FIGURE 5.11 Crackers baked on an Ashworth band.

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FIGURE 5.12

97

Baker Perkins cracker oven with pre-heat burners below the return

band.

FIGURE 5.13

Pre-heat burners positioned below the return band.

5.2.2 Oven insulation The baking chamber must be effectively insulated to minimise the heat loss from the oven to the bakery. Heat is conducted from the walls of the baking chamber through the insulation to the outer covers. The amount of heat conducted depends on the material, quality and density of the insulation. Materials such as mineral wool, normally used for oven insulation, have low thermal conductivity. Mineral wool is manufactured from molten rock, stone, glass or slag, which is spun into fibres. The mineral wool is supplied loose or compacted into mattresses. The mineral wool

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typically has a thermal conductivity, k, measured in watts per metre Kelvin of 0.06
0.10 W/(m K) at baking temperatures and is used at densities of 60
140 kg/m3 (Fig. 5.14).

FIGURE 5.14 Mineral wool insulation slabs for oven insulation.

5.3 Convection Convection is the movement that occurs in a fluid medium, for example, the air in the baking chamber. Hot air is less dense than colder air and will rise in the baking chamber. This is an important issue in the design of the temperature control systems since a change in temperature at the bottom of the oven will affect the temperature at the top. Convection is described by Newton’s Law of Cooling, which states that ‘the rate of heat transfer is proportional to the differences in temperatures between the body and its surroundings’.

5.3.1 Convection baking The term convection is used in the biscuit industry to describe a heat transfer system employing jets of hot air blown directly onto the surface of the dough piece and the oven band from above and below. This hot air increases the temperature of the surface of the dough pieces and removes moisture from the surface of the dough pieces (Fig. 5.15).

FIGURE 5.15 Convection.

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The convection system is very efficient at removing moisture during the middle part of the baking process. The hot, moving air constantly impinges on the surface of the dough pieces, rapidly evaporating moisture and removing it from the baking chamber through the extraction system. The convection baking system is usually controlled by altering the temperature of the air which is blown by the circulating fan into the baking chamber at a constant speed and volume. This convection system only affects the surface of the dough pieces and primarily the top surface as the bottom of the dough piece is fully or partly shielded by the oven band. In the case of a steel band or heavy mesh band, the heat transfer to the base of the dough piece is solely by conduction. The effect of the impingement of the hot air jets on the surface of the dough pieces is to dry the surface rapidly, and this will form a dry, hard skin which will then rise in temperature and increase in colour. Since a large volume of hot air is being blown evenly across the dough pieces, the colour will tend to be even and will not show highlights and patterns as achieved by a radiant heat transfer system. The rapid drying of the surface of the dough pieces forms a hard skin and prevents the expansion and ‘lift’ of the dough pieces so that convection is not used in the first part of the oven when baking crackers and most biscuits and cookies. In the first one-third of the oven length, convection should be at a minimum to prevent the skinning of the dough pieces and allow the texture, volume and shape of the products to develop. Applied in the final zones of the oven, convection will provide an even bland colour for biscuits such as Marie and assist in reducing the moisture content.

5.4 Summary 5.4.1 Radiation Radiation is the most important method of heat transfer for biscuit baking. It occurs by electromagnetic radiation of IR wavelengths from direct gas burners, the hot surfaces of the baking chamber and tubes or ducts carrying hot gases from the burners. This radiant heat is penetrative and efficient and occurs without adverse side effects, such as the rapid drying or skinning of the surface of the dough pieces. We have noted that the radiation is dependent on several factors: 1. The nature and consequent emissivity of the radiating surface (how close it is to a ‘black body’).

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2. The distance between the radiating surface and the dough pieces. The thermal energy transferred is inversely proportional to square of the distance. A small decrease in the distance causes a large increase in heat transfer to the dough pieces. 3. The difference in temperature between the radiating surface and the dough pieces. A small increase in the temperature of the radiating surface causes a very large increase in the heat transfer. The heat transfer is proportional to the temperature of the radiating surface to the power of 4 in Kelvin. 4. Radiation is the traditional method of heat transfer for baking biscuits and bread, as well as many other foodstuffs. It is the optimum heat transfer method for establishing quality texture, volume, shape and colour of biscuits. It is stable, penetrative and flexible, providing high heat inputs for crackers and a slow, ‘gentle’ heat transfer for soft doughs.

5.4.2 Conduction 1. Baking: Conduction transfers heat from the oven band directly to the base of the dough pieces. The heat transfer is dependent on the temperature and heat mass of the oven band and the surface of the band in contact with the dough piece. With steel bands and compound balanced weave bands, this approximates to full contact. Ovens with band pre-heat can quickly transfer heat into the base of the dough pieces and achieve rapid development of the biscuit structure and texture; this is particularly valuable for cracker baking. Conduction is also important in baking soft doughs on steel bands. 2. Oven insulation: Heat from the baking chamber is conducted to the oven outer covers and contributes to the heat loss to the bakery. Insulation material with low thermal conductivity is used to reduce this heat loss.

5.4.3 Convection 1. Convection baking uses hot air jets which impinge directly on the top of the dough pieces and the underside of the oven band. This system efficiently dries and colours the surface of the dough pieces. However, it produces a hard, dry skin on the dough pieces and will prevent good expansion and ‘lift’ of the product if used at the start of the baking process. 2. The convection of air in the baking chamber, where hotter air will rise must be taken into account when controlling oven top and bottom temperatures independently.

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3. Convection baking is favoured by oven manufacturers as it is relatively low cost to build and has a very simple control system. The burner power (total heat input to the baking chamber) is the main baking control in each zone. Most convection ovens have a fixed speed circulating fan and simple dampers to adjust the percentage of top to bottom airflow (Fig. 5.16).

FIGURE 5.16

Heat transfer by radiation, conduction and convection.

Further reading Chavan, R.S., Chavan, S.R., 2010. Microwave baking in food industry: a review. Int. J. Dairy. Sci. 5, 113
127. http://www.onlinelibrary.wiley.com, 2021. Department of Physics, 2021. University of Winnipeg. Heat transfer. http://www.theory. uwinnipeg.ca/physics eFunda, 2015. Heat Transfer. http://www.efunda.com Food Science and Food Safety, 2021. Infrared Heating in Food Processing: An Overview, Vol 7, 2008. http://www.researchgate.net Helios Italquartz Srl, 2021. http://www.heliosquartz.com Heraeus Noblelight, 2021. www,heraeus.com HyperPhysics, 2021. Georgia University: Heat transfer. http://hyperphysics.phy-astr.gsu.edu Institute of Food Technologists, 2022. Infrared Heating in Food Processing, Comprehensive Reviews in Food Science and Safety, Vol. 7, 2008. http://www.ift.org. Journal of Culinary Science and Technology, 2021. Effect of Far-Infrared Oven on the Qualities of Bakery Products, 6(2
3) 105
118, 2008. http://www.researchgate.net. Kerone, 2021. Industrial Heating System for Biscuit and Cookies Baking, 2016. http:// www.kerone.com Koral, T., 2021. Radio Frequency Heating and Post Baking. http://www.koralassociates.com McQueen Cairns, 2021. Hygrox. http://www.mcqueen-cairns.com. Mihalos, M., 2021. New food magazine. Effect of Oven Modes on Baking Unit Operations. Russell Publishing, United Kingdom. http://www.newfoodmagazine.com.

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Molecules, 2021. A Comprehensive Review on Infrared Heating, 2019, 24, 4125. http:// www.mdpi.com, 2021. Monga A., 2021. Radio Frequency Applications in Bakeries. http://www.strayfield.co.uk Physicalgeography.net, 2021. The Nature of Radiation. http://www.physicalgeography.net. Shiffmann, R.F., 1993. Microwave technology in baking. Springer, Boston. http://www. linkspringer.com, 2021. Taftan Data, 2021. Thermodynamics. http://www.taftan.com/thermodynamics Wade, P., 1987. Biscuit baking by near infrared radiation. J. Food Eng. 6, 165
175. http:// www.mdpi.com, 2021.

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6 Oven designs Biscuit baking ovens, generally known as tunnel ovens, have long conveyors which carry the dough pieces through a heated box section baking chamber. Oven lengths vary typically between 25 and 100 m long. The conveyor band material is a wire-mesh or a carbon steel sheet, which turns around large cylindrical drums at each end of the oven. The conveyor is driven by a variable-speed drive at the oven end which allows the operator to adjust the baking time.

6.1 Heat transfer methods The baking chamber may be heated directly with gas burners or electric heaters or by an indirect system using heat exchangers. Direct heating systems use gas or electricity, and indirect systems may also use diesel oil fuel as the products of combustion do not enter the baking chamber. The baking chamber is divided into zones along the length of the oven. Usually each control zone is between 8 and 20 m long. Each zone has independent control of temperature and humidity. This allows conditions throughout the baking process to be optimised for achieving the biscuit structure, moisture content and colour as the dough pieces travel through the oven. The control of the humidity in the baking chamber and the removal of moisture from the dough pieces are accomplished by an extraction system in each zone. This consists of ducts which draw air and moisture from the baking chamber through a fan and expel the air through vertical flues (chimneys) to the atmosphere. In some ovens, this wet air removed from the baking chamber can be diverted either to the flue or back into the baking chamber. This provides moving humid air within the baking chamber which can aid heat transfer and contribute to even baking conditions across the

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width of the oven. These systems are called ‘turbulence’ systems and are mainly used on ovens which have relatively still air in the baking chamber, for example, indirect radiant ovens and direct gas-fired ovens. Ovens are designed to optimise the heat transfer to the dough pieces in different ways using radiant heat, conduction and convection.

6.1.1 Radiant heating Direct gas-fired ovens, electric ovens and indirect radiant (‘cyclotherm’) ovens (Fig. 6.1).

FIGURE 6.1 Baker Pacific direct gas-fired/indirect radiant oven.

Infrared radiant energy penetrates the dough pieces and creates the volume and texture of the products. It is essential in the first third of the baking process. The penetration of the dough pieces is determined by the wavelength of the radiation. For food products including dough pieces, the maximum absorption is achieved at near-infrared wavelengths from 2.7 to 5.9 µm.

6.1.2 Conduction heat transfer Ovens with pre-heated compound balanced weave bands and steel conveyor band conduct heat into the base of the dough pieces. The heat is then conducted within the products (Fig. 6.2).

Biscuit Baking Technology

FIGURE 6.2 Cake baked on a steel band.

6.1.3 Convection baking Direct and indirect convection ovens transfer the heat by blowing hot air jets onto the products. Also ‘Re-circ’ ovens combine convection and radiant heat transfer (Fig. 6.3).

FIGURE 6.3 Baker Perkins indirect convection oven.

The convective air impinges on the surface of the products and is effective in evaporating moisture from the surface.

6.2 Radiant heating 6.2.1 Direct gas-fired ovens Direct gas-fired ovens are very widely used throughout the biscuit baking industry. They offer versatility to bake all types of biscuits, cookies and crackers.

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The direct gas-fired oven has a simple baking chamber of box section with the oven band supported through the middle of the chamber. Ribbon gas burners are located above and below the band. A gas/air mixture is supplied to the burners, and this is ignited by a spark electrode and burns on a strip or ribbon across the width of the oven conveyor band (Fig. 6.4).

FIGURE 6.4 Baker Pacific direct gas-fired oven.

The heat transfer in a direct gas-fired oven is primarily by radiation from the gas flames and from the oven top, base and walls of the baking chamber (Fig. 6.5).

Extraction fan

Combustion air fan Extraction ducts

Gas supply Air supply DGF burners FIGURE 6.5 Direct gas-fired baking chamber.

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Most types of gas may be used including natural gas, town gas (manufactured from coal) and LPG (liquid petroleum gas). The burners operate with a ‘zero gas pressure’ gas system. The pressure of the combustion air supplied to the burners is controlled by motorised valves or variable-speed blowers to increase or decrease the flame intensity and heat input. Various designs of corrugated stainless steel strips (or ribbons) are used to give a range of heat ratings. Woven wire-mesh (metal fibre) strips are also used for high infrared heat ratings. This type of oven can achieve high heat inputs per square metre of band surface. Heat input of 45,000 kcal/m2 of oven band area may be used for cracker baking. Direct gas-fired ovens can successfully utilise any type of baking band, compound balanced weave, open wire-mesh bands and steel bands. Direct gas-fired burners are used to supply band pre-heat where this is required for cracker baking (Figs. 6.6 and 6.7).

FIGURE 6.6 Direct gas-fired metal fibre burners.

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FIGURE 6.7 Burner head with gas/air mixer, gas solenoid valve, ignition and flame detection electrode.

The heat mass and stable radiant heat can be increased by installing heavy tiles at the top and bottom of the baking chamber. This arrangement is successfully used in the baking of water biscuits and crackers requiring very high heat inputs and stable radiant heating.

6.2.2 Conversion to electrical heating The Baker Pacific direct gas-fired oven can be converted to electric heating. The gas burners are removed and replaced by electric heating elements mounted on frames which slide into the baking chambers (Fig. 6.8).

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FIGURE 6.8 Replacement of gas burners with electric heating elements.

6.2.3 Summary 1. Direct gas-fired ovens provide radiant heat over a wide range of heat inputs. 2. Rapid and responsive control of heat input and accurate temperature control. 3. Suitable for all types of products: crackers, cookies, all types of biscuits.

6.2.4 Electric ovens The electric oven provides infrared radiant energy from electric elements in the baking chamber above and below the band. The infrared radiant energy penetrates the dough pieces and creates the volume and texture of the products (Fig. 6.8). The electric oven has several features contributing to high efficiency: 1. The low thermal inertia of an electric infrared radiation heating system gives a fast response and quickly reaches the baking temperature. The radiant energy is absorbed by the dough pieces and is immediately converted to heat. 2. The electric heaters do not produce combustion products, so there is no contamination of the product or atmosphere. 3. In an electric oven only, the moist air is extracted from the baking chamber to achieve the correct moisture content for the products. 4. Electric ovens have a relatively short heat up time and the heat input is controlled accurately from 0% to 100%. 5. Electric radiant heaters are easily and precisely thermostatically controlled. Power control devices are thyristors, which control the current by varying the resistance.

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6. Electric heating systems can be specified for all types of biscuits. Heat ratings for crackers, semi-sweet, short dough biscuits and cookies can be achieved. 7. Electric heating systems have low maintenance requirements compared to gas-fired ovens. Electric ovens are constructed in a similar way to direct gas-fired ovens, but use electric heating elements in place of the gas burners. These ovens have been widely used in the baking industry in some countries where industry had adequate electricity supply, but lacked gas, for example, China. However most countries, including China, now use gas fuel predominantly in the baking industry, which is currently substantially cheaper than electricity. Electrical heating has also been used in the first zones of ovens which required high heat inputs at the start of the baking process and where diesel oil with an indirect heating system was the preferred fuel for the main part of the oven (Figs. 6.9 and 6.10).

FIGURE 6.9 Electric oven in China.

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Extraction / turbulence fan

Turbulence ducts

Oven band

Electric heaters

FIGURE 6.10

Electric oven baking chamber with turbulence system.

6.2.5 Summary 1. Electrical energy is clean, does not require storage and is easily controlled. 2. Electric ovens can be simply controlled by thyristor units which vary the current in the elements and hence the heat input to the baking chamber. 3. Suitable for all types of crackers, cookies and biscuits. 4. Provides a very dry atmosphere in the baking chamber and may require steam injection in the first zones for some products. 5. Currently expensive to operate in most markets and not widely used now. However with the pressure to reduce reliance on fossil fuels and the substantial reduction in the cost of electricity from renewable energy sources, there is growing interest in electric ovens.

6.2.6 Indirect radiant ovens The indirect radiant ovens (also known as ‘cyclotherm’ ovens) are constructed in separate zones. Each zone is typically 10 20 m long and has a single burner, heat exchanger and circulation system for the hot gases from the burner (Fig. 6.11).

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FIGURE 6.11 Baker Pacific indirect radiant oven.

Each zone has a burner firing into a burner tube. The hot burnt gases are drawn from the burner tube through ducts to rows of steel tubes, or ducts, at the top and bottom of the baking chamber. These radiant tubes, or ducts, run the whole length of the zone. The hot gases travel through the tubes or ducts which radiate heat to the products from above and below. At each end of the zone, the hot gases are collected in a return duct through which they travel back to the circulating fan and from there to the burner tube to be re-circulated. It is essentially a closed, circulating system with a single burner, circulating fan and radiant tubes to heat the products from above and below (Fig. 6.12). Burner flue (for heat recovery system) Top radiant tubes Distribution ducts Return ducts

Header duct Bottom radiant tubes Circulating fan

Oven band

Gas or oil burner

FIGURE 6.12 Indirect-fired radiant heating system.

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A flue with natural convection is used to balance the pressure in the system resulting from the ingress of combustion air at the burner. The continuous re-circulation of the hot gases ensures a good efficiency. Fresh air is only drawn into the system at the burner for combustion, and this is balanced by the natural extraction through the burner flue. Since the products of combustion do not enter the baking chamber, the burner may use diesel oil or gas. This system has been commonly used where oil was the most economic fuel, for example, in India. The indirect radiant baking system bakes by radiation with a high heat mass providing stable baking conditions. It is versatile, capable of baking all types of biscuit, cookies and some crackers. High-rate crackers require the first zones with direct heating. The system is favoured by many bakers for producing a high quality of biscuit structure, texture and colour. It is an ideal system for achieving colour contrasts on rotary moulded and cracker products (Fig. 6.13).

FIGURE 6.13

Indirect radiant baking oven.

6.2.7 Summary 1. Indirect radiant ovens provide a very stable, radiant heat, preferred by many bakers. 2. The ‘closed’ circulation system retains and re-circulates the hot gases from the burner and contributes to good fuel efficiency. 3. Suitable for all types of products, except for the first zone(s) of ovens for baking high-rate crackers which required direct heating. 4. Suitable for all types of fuel including diesel oil.

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6.3 Turbulence systems The heat transfer in radiant heating systems in direct gas-fired ovens, electric ovens and indirect radiant ovens is enhanced by the movement of humid air in the baking chambers. This is provided by turbulence systems. In all ovens, moist air is extracted from the baking chambers to the atmosphere as the moisture content of the dough pieces is reduced. The turbulence systems divert some of this moist air to ducts or tubes across the baking chamber above and below the oven band. Dampers allow the proportion of this moist air to be adjusted to top or bottom turbulence or to the extraction flue to the atmosphere (Fig. 6.14).

FIGURE 6.14 Turbulence system.

6.4 Conduction heat transfer As noted above, steel baking bands and heavy mesh bands conduct heat rapidly into the base of the dough pieces. These types of band can be used in any of the oven designs, direct gas-fired, indirect radiant ovens and convection ovens. Steel bands are made of carbon steel, usually 1.2 mm thick. They are principally used for the baking of cookies with high sugar and fat contents, which flow on the oven band in the first part of the oven. Snack cakes are also deposited and baked on steel bands. Traditionally steel bands are also used for the baking of ‘Marie’ biscuits (Fig. 6.15).

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FIGURE 6.15

Cookies deposited directly onto a steel band from a wire-cut machine.

Compound balanced weave baking bands, mainly type CB5, are woven with a tight ‘herring bone’ pattern providing a solid, thick, heavy mesh. These bands are pre-heated to 120 C 150 C, and they conduct heat immediately into the base of the dough pieces as soon as they are deposited onto the band. This is a major baking method, being used throughout the industry for the baking of soda crackers and saltines. These bands are also versatile and can be used for a wide range of crackers, hard sweet and rotary moulded products (Figs. 6.16 and 6.17).

FIGURE 6.16

CB5 oven band from Rexnord Cambridge Engineered Solutions.

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FIGURE 6.17 Baker Perkins direct gas-fired cracker oven with pre-heat burners below the return band.

6.5 Convection baking Convection ovens are constructed in zones, each zone having a single burner and circulation fan. The fan blows the air around the burner tube or through the heat exchanger, where it is heated and then through ducts along the length of the zone. These ducts, located above and below the baking band, have slots or nozzles through which jets of hot air are blown onto the products and the oven band. Hot air from the baking chamber is drawn back to the fan to be re-circulated through the system. Each zone has an extraction fan and flue to remove moisture from the baking chamber, and this system will also extract some of the hot air from the heating system. Convection ovens generally have fixed speed fans. Typically, the discharge velocity of the air from the nozzles is a maximum of approximately 20 m/s at a maximum temperature of 310 C 320 C. The control of the baking process is therefore by temperature by modulating the burner and by adjusting the proportion of convective air diverted to the top or bottom ducts. The airflow to the top and bottom of the oven is controlled by separate top and bottom manual or motorised dampers. Temperature control is by thermocouples detecting the temperature of the convective air above and below the oven band. The thermocouples are connected to temperature controllers in each zone which will automatically adjust the burners to increase/decrease the heat input.

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6.5.1 Direct convection ovens The hot gases from the burner are combined with the re-circulated air from the baking chamber and blown through the ducts in the baking chamber and directly onto the products. As the products of combustion are blown directly onto the products, diesel oil fuels are unsuitable for direct convection baking (Figs. 6.18 and 6.19).

FIGURE 6.18

Direct convection baking system (after Haas-Meincke).

FIGURE 6.19

Convection baking system.

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6.5.2 Indirect convection ovens The burner fires into a burner tube connected to a multi-pass heat exchanger. The products of combustion are circulated within the heat exchanger and do not enter the baking chamber. Air is drawn from the baking chamber through the circulating fan and then passed through the heat exchanger, where it picks up heat, before being blown through the ducts in the baking chamber and onto the products. This system can utilise gas or diesel oil fuels (Fig. 6.20).

FIGURE 6.20 Indirect convection oven with heat exchanger (after Haas-Meincke).

Convection ovens can also employ electrical heater units. The duct heaters replace the gas burners and heat exchangers (Fig. 6.21).

FIGURE 6.21 Electric duct heater from DhE Thermowatt.

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6.5.3 Summary 1. Convection ovens bake by blowing hot air onto the product surface, so this is not a heat transfer system which optimises the development of biscuit volume and structure. 2. Unsuitable for the first zone(s) of the oven for most products as the convective air dries and skins the surface of the dough pieces preventing good lift and expansion. 3. Convection ovens are suitable for cookies which are moulded or deposited onto a steel band and remain a similar size during the baking process. An example is the baking of Danish Butter Cookies. 4. Effective system for drying dough pieces to low moisture contents in the final oven zones. This rapid drying occurs at the product surface and may contribute to an excessive moisture gradient in the biscuit and consequent ‘checking’ or cracking of the packaged biscuits. 5. Provides even, bland colouring of the biscuits without contrasts, suitable for products such as Marie. 6. Direct convection ovens are relatively low cost ovens to construct and control.

6.5.4 ‘Re-circ’ ovens These ovens were developed in the United States as a versatile pet food and biscuit oven. The system is a direct convection oven, but the volume of hot gases blown directly onto the products can be adjusted. When this is reduced, the hot gases circulate through the ducts at the top and bottom of the oven and return to the burner tube, with less hot air being blown onto the products. The system can therefore balance the heat transfer by convective air or by radiation from the ducts. Re-circ ovens may be used for products requiring lower heat inputs. For the first zones, the oven is operated in a mainly radiant mode to avoid ‘skinning’ the dough piece. However, the heat transfer in this mode is low, and the biscuit structure is relatively slow to form. In the convective mode, the heat transfer is increased and the system operates as a direct convection oven (Fig. 6.22).

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FIGURE 6.22 Baker Perkins Re-Circ oven.

6.5.5 Summary 1. Suitable for general baking of products requiring relatively low heat inputs. 2. Unsuitable for diesel oil fuels.

6.6 Hybrid ovens It has become common practice to combine different oven types into a ‘hybrid’ or ‘combination’ oven. This allows the baker to use different heat transfer modes at different stages of the baking process.

6.6.1 Direct gas-fired/indirect radiant ovens Products such as crackers and semi-sweet biscuits require high heat inputs in the first part of the baking process to establish good structure and volume. This can only be provided effectively by a direct heating system and a direct gas-fired oven section is normally specified. This system also minimises the drying and skinning of the surface of the dough pieces, which would prevent the lift and expansion of the dough pieces. The length of this direct-fired section is usually one-third of the total length of the oven and the power input of the direct fired section is one half of the total power input of the oven.

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The indirect radiant oven section will contribute to the optimum development of texture and colour of a wide range of crackers and biscuits (Fig. 6.23).

FIGURE 6.23

Baker Pacific hybrid oven: direct gas-fired/indirect radiant.

6.6.2 Direct gas-fired/convection ovens This specification again uses the benefits of the direct gas-fired oven in the first third of the oven. The convection section will effectively remove moisture from the dough pieces and achieve a low and even moisture content for the final product. Colour will be even and bland, without contrasts, which is suitable for a range of hard sweet biscuits (Fig. 6.24).

FIGURE 6.24 Dingson Food Machinery hybrid direct gas-fired/indirect convection oven.

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Further reading Baker Pacific Ltd, 2021a. Cambridge CB24 9YZ, United Kingdom. http://www.bakerpacific.net. Baker Perkins Ltd, 2021b. Manor Drive, Paston Parkway, Peterborough, PE4 7AP, United Kingdom. http://www.bakerperkins.com. Bu¨hler Group, 2021. Gupfenstrasse 5. CH-9240 Uzwil, Switzerland. http://www.buhlergroup.com. Chavan, R.S., Chavan, S.R., 2010. Microwave baking in food industry: a review. International Journal of Dairy Science 5, 113 127. http://www.onlinelibrary.wiley. com. Davidson, I., 1989. A Baker’s Guide to Modern Biscuit Ovens. Japanese Biscuit Makers Association. DhE srl. Thermowatt Spa, Via Batistta 21, 60011 Arcevia AN, Italy. http://www.dhesrl. com. Dingson Food Machinery Ltd, 2021. Address: No. 13, Tengyun Road, Tanzhou Town, Zhongshan City, Guangdong Province, 528467, China. http://www.dsm-mc.com. Food Science and Food Safety, 2021. Infrared Heating in Food Processing: An Overview, Vol 7, 2008. http://www.onlinelibrary.wiley.com. Helios Italquartz, 2021. S.r.l. Via delle Industrie 103/A 20040, Cambiago, Milano, Italy. http://[email protected]. Heraeus Nobelight Ltd, 2021. 161 Cambridge Science Park, Milton Rd, Cambridge CB4 0GQ, United Kingdom. http://www.heraeus.com. Institute of Food Technologists, 2021. Infrared Heating in Food Processing, Comprehensive Reviews in Food Science and Safety, Vol. 7, 2008. http://www.onlinelibrary.wiley.com. Journal of Culinary Science and Technology, 2021. 6(2 3) 105 118, 2008. Effect of FarInfrared Oven on the Qualities of Bakery Products. http://www.researchgate.net. Kerone, 2021. Industrial Heating System for Biscuit and Cookies Baking, 2016. http:// www.kerone.com. Koral, T., 2021. Radio Frequency Heating and Post Baking. http://www.strayfield.co.uk. Mihalos, M., 2021. New food magazine. Effect of Oven Modes on Baking Unit Operations. Russell Publishing, United Kingdom. http://www.newfoodmagazine.com. Molecules, 2021. A comprehensive review on Infrared Heating, 2019, 24, 4125. http:// www.mdpi.com. Monga, A., 2021. Radio Frequency Applications in Bakeries. http://www.strayfield.co.uk. S. Eldridge Design Ltd, 2021. 37 Hazelwood Cl, Honiton EX14 2XA, United Kingdom. http://www.seldridgedesign.co.uk. Shiffmann, R.F., 1993. Microwave Technology in Baking. Springer, Boston. http://www. linkspringer.com. Thermowatt spa, 2021. Thermowatt Spa, Via Batistta 21, 60011 Arcevia AN, Italy. http:// www.thermowatt.com. Wade, P., 1987. Biscuit baking by near infrared radiation. J. Food Eng. 6, 165 175. http:// www.researchgate.com.

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7 Oven specifications 7.1 Specifications for ovens: crackers A quality cracker has several important characteristics which are highly influenced by the baking process: • an open, light, flaky texture; • a surface colour which may have highlights (that is dark raised areas and lighter background areas); • toppings of cheese, herbs and spices which should have a distinctive definition; and • low-moisture content, around 1% 2% (Fig. 7.1).

FIGURE 7.1 Crackers.

The baking oven specification is critical to ensure the dough pieces are baked to achieve the specific qualities of texture, moisture content and appearance required.

7.1.1 Development of structure and texture The development of the light flaky texture occurs during the first 30% 40% of the baking process. This change in structure involves the formation and expansion of gases and an increase in water vapour pressure which together give a dramatic increase in volume. Simultaneously, softening of the fats, swelling and gelatinisation of starch and the denaturation of proteins occur. These changes cause the cracker structure to form.

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The increase in volume must occur as the structure is forming but before the outer surface of the products becomes dry and rigid. The dough pieces require a rapid, high level of heat transfer, with maximum penetration. It is necessary to delay the drying and setting of the top surface of the product as far as possible to allow maximum ‘lift’ and expansion. This requires that the baking chamber is humid and the surface of the dough piece remains moist. The humidity of the baking chamber may be assisted by the injection of steam at the feed end of the oven. To achieve the correct conditions for good cracker development, it is necessary to apply maximum heat, of the order 40 50,000 kcal/h per m2 of oven band area. Heat is applied to the base of the dough pieces and by conduction to the centre of the product immediately it enters the oven. This may be done in two ways: Firstly, by the use of Compound Balanced Weave bands which are pre-heated to temperatures up to 150 C. These heavy bands conduct heat immediately to the base of the dough pieces and then through the dough piece causing rapid expansion of the gases and water vapour and consequent lift of the product. This applies particularly to US practice of baking crackers such as soda crackers. Alternatively (and we may use the example of traditional British practice in the baking of cream crackers), a lighter open mesh band (5 3 5) is used and the bottom heat is applied by radiation from direct gas burners. Again high heat inputs of 40,000 kcal per m2 of band are achieved. The heat transfer from the burners is primarily through infrared radiation which penetrates the dough pieces.

7.1.2 Reducing moisture content Cracker biscuits also require considerable amounts of water to be removed. The dough pieces entering the oven may typically be at a moisture content of 15% 25% and this must be reduced to 1.5% 2.5% in the finished product. Reducing moisture content requires convective air. The moving air removes the moisture from the surface of the product. It also prevents a build-up of a static moisture barrier around the product which would inhibit further rapid moisture loss. It is important that moisture is removed from within the product and a minimum moisture gradient from the middle to the outside of the product is achieved. If this moisture gradient is too high, stresses in the final product will cause checking (cracks which cause breakage of the biscuit after cooling). This convective air is provided by a turbulence system in a direct gas-fired oven.

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7.1.3 Colour Colour changes occur when yellow and brown dextrins form and the sugars caramelise. This occurs at around 150 C 160 C in the final zones of the oven. Direct gas-fired zones with turbulence are preferred. Convection heat transfer may cause the edges of the crackers to pick up colour very quickly, causing ‘ringing’, crackers with dark edges. Most crackers have highlighted colour over the surface of the product. This is achieved by the predominant use of radiant heat in a direct gas-fired or indirect radiant in the final oven zones.

7.1.4 Final moisture content The final moisture content of crackers is low (1.5% 2.5%) and must be consistent. It is also important that the moisture gradient from the surface to the centre of the product is low. In this respect, the application of dielectric heating has been successful. The use of frequencies within the ranges of 13.56, 27.12 and 40.68 MHz gives several inherent advantages in achieving low and even moisture contents in the final product. The heat is generated within the products in proportion to the moisture content, thus very even, consistent and low-moisture contents can be achieved throughout the biscuit structure. However, care must be exercised when baking products with inclusions or toppings such as cheese or fruit as these may present pockets of high moisture which may be burnt by dielectric heating. Dielectric sections placed after direct gas-fired (DGF) oven can often increase throughout and improve moisture control of the finished product. However, the dielectric units require the use of synthetic bands and are therefore constructed separately with a separate band circuit.

7.1.5 Recommended specification for a cracker oven Specification of a combination oven for snack crackers (e.g. ‘TUC’ or ‘Ritz’ types) (Table 7.1 and Figs. 7.2 7.4). TABLE 7.1

Oven for snack crackers.

Process requirement

Heat transfer method

Oven zone

Product development and formation of structure

Radiant

DGF with oven band preheat

Reducing moisture

Radiant/convection

DGF with turbulence

Colouring

Radiant/convection

DGF with turbulence

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FIGURE 7.2 Baker Perkins Direct Gas Fired Oven with preheat and CB5 or Z47 band.

FIGURE 7.3 Compound Balanced Weave band from Ashworth Bros., United States.

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FIGURE 7.4 Steinhaus GmbH: F4012 (Z47 type).

7.2 Recommended oven specification for light carrier products, for example crispbreads, rusks Dry, light carrier products represent a wide range but with similar process requirements (Fig. 7.5). They all require to be dried to even, very-low-moisture levels. The reduction of moisture contents varies from 20% 27% in the dough piece down to less than 1% in the finished product in some cases.

FIGURE 7.5 Crispbreads and rusks.

Good control for very even colour and establishment of correct structure is required. However, the development of the structure and

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colour does not demand the very stringent conditions required for crackers. Unlike soft dough biscuits, which often have a surface design and crackers which may have a highlighted appearance, many carrier products have a flat evenly coloured surface. These products are often formulated with wholemeal flours, rye and bran to enhance their healthy eating quality. Many are therefore dark in colour. The important characteristic is a low and even moisture content. This can be achieved with several heat transfer methods provided the baking time is sufficiently long. However, the most efficient method is convection which achieves the best economies of fuel, space and the highest outputs. Care must be taken in the final 30% of baking to prevent edge burning. A correct baking profile is therefore required. Minimal spacing of the product on the oven band or baking in continuous sheets will also reduce edge colouring and improve throughput. For this range of products therefore convection ovens are often preferred (Table 7.2 and Fig. 7.6).

TABLE 7.2 Oven for crispbreads and rusks. Process requirement

Heat transfer method

Oven zone

Product development and formation of structure

Radiation/conduction

DGF with oven band preheat

Reducing moisture

Convection

Convection or DGF with turbulence

Colouring

Convection or radiation

Convection or DGF with turbulence

FIGURE 7.6

Hybrid direct gas-fired/convection oven from Ariete Brazil.

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7.3 Recommended oven specification for semi-sweet biscuits, for example Marie Good quality semi-sweet biscuits have the following characteristics: • • • • • •

Good volume to give low-density and a light product Smooth homogeneous texture Crispy bite Very even colour Low-moisture content Very even moisture content to avoid checking (Fig. 7.7)

FIGURE 7.7 Semi-sweet biscuits.

An even radiant heat is required to achieve good volume in the first third of the oven. The dough piece must not be ‘skinned’ or ‘case hardened’ and should increase substantially in volume. This gives a low-density, light crispy bite. Semi-sweet doughs have considerable water content (around 20%) and this must be reduced to 2% 3% in the baked product. It is essential to achieve an even moisture content and avoid a moisture gradient from the centre to the outside of the biscuit, as this would lead to checking. The baking time must be sufficiently long and gentle. This can be achieved by radiant heat from a DGF or indirect radiant oven or a hybrid DGF/convection oven. The colour of hard sweet biscuits is generally very bland and even. This may be achieved by any of the main oven types. Convective air from a convection zone is beneficial. For products with a serious checking problem, dielectric heating may be considered. However, this is expensive in capital cost and running cost. Checking can be avoided by careful baking with adequate baking time on a conventional oven (Table 7.3 and Fig. 7.8).

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TABLE 7.3 Oven for semi-sweet biscuits. Process requirement

Heat transfer method

Oven zone

Development of structure and texture

Radiation

DGF

Reducing moisture

Radiation/Convection

Convection or DGF with turbulence

Colouring

Convection

Convection or DGF with turbulence

FIGURE 7.8 Direct gas-fired from Dingson Food Machinery.

7.4 Recommended oven specification for short dough biscuits Rotary moulded biscuits represent a wide variety of shapes, which are baked to give an attractive appearance (Fig. 7.9).

FIGURE 7.9 Short dough biscuits.

• The short doughs have low-moisture content. • Higher fat and sugar than hard doughs, less development of volume.

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• • • •

Generally baked on Z47-type wire-mesh oven bands. Often baked with relatively short baking times, 3.8 min being typical. Rotary moulded biscuits are often produced in large quantities. Many rotary moulded biscuits have a design requiring highlights, pale background and darker pattern. This is best achieved by radiant heat transfer (Table 7.4 and Fig. 7.10).

TABLE 7.4

Oven for short dough biscuits.

Process requirements

Preferred heat transfer method

Oven zone specification

Formation of structure and texture

Radiant

DGF or indirect radiant

Reducing moisture

Radiant

DGF or indirect radiant with turbulence

Colouring

Radiant

DGF or indirect radiant with turbulence

FIGURE 7.10

Baker Pacific Indirect Radiant oven with turbulence.

7.5 Specifications for ovens: soft dough cookies Soft dough cookies, particularly those with large inclusions such as chocolate chips or nuts or centre fillings present quite different baking requirements. The quality product must have the following characteristics:

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• High degree of flavour, for example fruit, nut or chocolate. These flavours must be preserved during the baking process. • The flavour of the dough also, both its crust and its filling, must be enhanced. • A distinctive eating quality which may require a soft centre and a crisp outer surface. An attractive surface appearance which may in some cases be gilded or sugar coated. • A shape which may require a degree of flow on the oven band (Fig. 7.11).

FIGURE 7.11 Cookies.

In general, cookies are much thicker and heavier than the crackers and with high fat content and they may also have levels of moisture in the dough of around 10% 15%. Baking times are considerably longer, from 7 9 min for many deposited biscuits and up to 12 14 min for filled products. The baking band also has an important influence on the heat transfer methods used. Cookies are baked on steel bands and these act as a barrier to convective air. Heat will only be transferred to the base of the biscuit by conduction from the steel band. During baking, the products which have high fat contents will flow on the steel band as the fat softens. This product flow takes place in the first part of the baking process. Subsequently, moisture levels must be reduced, and finally, the required colour and product appearance are achieved. Baking must be carried out slowly, gently and at relatively low temperatures to preserve the flavours and to allow good product flow on the band. In summary, a heat transfer method which achieves an even balance of top and bottom heat is required. To achieve these process requirements, radiant heat is preferred and a low baking temperature and relatively long baking time. The radiant heat may be applied by direct gas-fired or indirect radiant (cyclotherm) ovens. To achieve faster baking times convective oven zones may be used in the final stages of baking, particularly when the even, bland colouring produced is acceptable (Table 7.5).

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Oven for cookies.

Process requirements

Preferred heat transfer method

Oven zone specification

Product flow and formation of structure and shape

Radiant

DGF or indirect radiant

Reducing moisture

Radiant or convective

DGF or indirect radiant or convection

Colouring

Radiant or convective

DGF or indirect radiant or convection

7.6 Danish butter cookies Danish butter cookies comprise a mix of rotary moulded and deposited products baked on a steel band. The most popular oven specification is a convection oven. The cookies are relatively small in size, spread very little on the steel band, doughs have a low-moisture content and the colour required is even.

7.7 Modular oven design By considering the process requirements of each product we can therefore design an oven to enhance the particular characteristics of texture, eating quality, colour and appearance by the selective application of different methods of heat transfer. We have proposed some optimum configurations of ovens to produce certain quality products: crackers, dry carrier biscuits, semi-sweet biscuits, short doughs and cookies. A modular oven range includes the following types of zone. Each type of module is compatible in size and construction with those of other types and can therefore be incorporated in the same biscuit oven (Table 7.6). TABLE 7.6

Oven for crackers.

Heat transfer method

Oven zone type

Radiation

Direct gas-fired Indirect fired radiant Convection ovens Turbulence systems We can use different band types to assist or reduce conduction to the base of the biscuit, e.g. heavy mesh CB5, steel bands, open wire-mesh Z47 type

Convection Conduction

Direct product heating

Dielectric unit

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7.8 Calculation of oven zone lengths To calculate the best zone lengths for a particular oven specification, we need to consider the following: 1. The control we need to maintain the best baking profile for the oven. At certain stages of the baking process, we will need short zones to rapidly increase the baking temperature, at later stages the requirement may be a more steady, constant, stable temperature requiring less heat input and therefore longer zones will be suitable. 2. Flexibility of control. We can specify the zone lengths and heat input for a specific biscuit. However, normally we will allow some flexibility to alter baking profiles and alter conditions to bake other products. More control zones give greater flexibility. 3. The heat input or rating from the burners in terms kWh/m2 of oven band area. This is the heat energy which can be transferred to the dough piece in each zone. 4. The construction of the oven modules. Manufacturers have standard module lengths and zones are normally a multiple of these standard module lengths. For particular applications, special module lengths can be made. 5. Zone lengths normally vary between 8.0 and 18.0 m, though shorter or longer lengths may be made for particular circumstances.

7.8.1 Example 1: Direct gas-fired oven for baking crackers (1.5 3 100 m long) Our baking profile requires a high heat input over the first 30% of the oven length to raise the baking temperature to 300 C and then to maintain a temperature of 280 C in the middle of the oven. The final colouring stage will require less heat input to maintain a baking temperature of 250 C. The baker will determine the optimum baking profile for the product. This will be translated into a series of set temperatures and zone lengths. It is also necessary to consider maintaining flexibility to bake other products. For example we can specify zones with the same set temperatures for one product but may require different settings for another product. 7.8.1.1 Heat input Baker Pacific oven modules are 2.9 m in length and contain four top burner positions and four bottom burner positions. Our DGF burners

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are rated at 20 30 kW. In one module, we can input a total of up to 240 kW (Fig. 7.12).

FIGURE 7.12

Baker Pacific standard oven module.

Heat rating / input per square metre of oven band

The area of oven band in the module is 1.5 3 2.9 m 5 4.35 m2. The maximum heat rating that can be achieved is therefore 55.17 kWh/m2 with hi-rate burners. We can now divide the oven length into separate zones and specify the number and rating of the burners for each zone required to give the heat input to achieve our baking profile (Fig. 7.13).

50000kcal/m2 58 kWh/m2

40000kcal/m2 47 kWh/m2

30000kcal/m2 35 kWh/m2

20000kcal/m2 23 kWh/m2

+ band preheat 10000kcal/m2 12 kWh/m2

Zone 1 % of oven length 0

Zone 2 10

Zone 4

Zone 3 20

30

Zone 5

40

50

Zone 6 60

Proposed heat ratings for soda cracker oven DGF oven 1.5m × 100m

FIGURE 7.13 Heat rating for soda crackers.

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Zone 8

Zone 7 70

80

90

100%

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Our zone lengths will vary between 8.0 and 18.0 m and they will be designed to achieve a rapid heat input in the first oven zones, to maintain a high temperature throughout the middle zones and then to reduce the heat input for the final zones. It should be noted that a considerable amount of heat is carried through the oven with the oven band and products, so the heat input required will reduce in the later oven zones, 5 8. Our proposed oven zone heat ratings are shown above (Table 7.7; Fig. 7.14). TABLE 7.7 Zone lengths and ratings. Zone

1

2

3

4

5

6

7

8

8.7

8.7

11.6

11.6

11.6

14.5

14.5

17.4

13.0

13.0

17.4

17.4

17.4

21.7

21.7

26.1

Rating (kWh/m )

50

50

40

35

30

25

20

20

No. of burners (30 kW)

22

22

23

20

17

18

14

17

Length (m) 2

Area (m ) 2

FIGURE 7.14 Baker Pacific DGF oven with 2.9 m modules and Eratec MFB burners.

7.8.2 Example 2: Indirect radiant oven for baking a short dough biscuit, glucose type (1.25 m 3 100 m long) The rotary moulded short dough biscuits will require a longer bake time (3.8 min) and lower baking temperatures and heat inputs than crackers. The main aim will be to achieve a good biscuit texture, eating

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quality, flavour and colour. For this type of biscuit an indirect radiant oven is ideal. 7.8.2.1 Heat input In an indirect radiant oven, there is one burner per zone. On a Baker Pacific oven these are Weishaupt WG30 for natural gas with a power rating of 130 350 kW or WG40 with power rating of 240 550 kW. For dual fuel applications, Maxon OVENPAK515SP is suitable. The zones are made up from baking chamber modules of approximately 2.3 m long and heater modules 2.0 m long. The final zone(s) may be heated by the Heat Recovery System (Figs. 7.15 and 7.16; Table 7.8).

TABLE 7.8 Zone lengths and ratings. Zones

2

3

4

5

6

7

8

8.9

11.2

11.2

11.2

13.5

13.5

13.5

15.8

2

Area (m )

11.1

14.0

14.0

14.0

16.9

16.9

16.9

19.8

Heat input (kWh)

360

350

340

320

390

390

390

Heat recovery system

Heat rating / input per square metre of oven band

Length (m)

1

50000kcal/m2 58 kWh/m2

40000kcal/m2 47 kWh/m2

30000kcal/m2 35 kWh/m2

Heat recovery system

20000kcal/m2 23 kWh/m2

10000kcal/m2 12 kWh/m2

Zone 2

Zone 1 % of oven length 0

10

Zone 3 20

30

Zone 4 40

Zone 5 50

Zone 6 60

Proposed heat ratings for oven for short biscuits Indirect Radiant Oven 1.25m × 100m Maxon burners: maximum rating 366kW

FIGURE 7.15 Heat rating for short dough biscuits.

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Zone 7 70

80

Zone 8 90

100%

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FIGURE 7.16 Baker Pacific Indirect Radiant Oven with heat recovery system.

7.8.3 Example 3: Multipurpose oven 1.25 m 3 91.0 m Refer Fig. 7.17.

FIGURE 7.17 Examples of crackers, semi-sweet and rotary moulded biscuits for a multipurpose production line.

Heat ratings are shown below for four multipurpose ovens supplied for a multinational biscuit manufacturer. The ovens produced snack crackers, semi-sweet biscuits and short dough biscuits (Fig. 7.18).

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FIGURE 7.18

Heat ratings for multipurpose ovens.

The oven is flexible to achieve a range of baking profiles. It is a hybrid direct gas-fired/indirect radiant oven with turbulence to provide convective air. The oven band is an open wire-mesh Z47 type with preheat. A complete specification is given in Appendix 2 for a 7-zone oven. The first three zones are direct gas-fired followed by four zones of indirect radiant with turbulence (Fig. 7.19; Table 7.9).

TABLE 7.9

Zone lengths and ratings.

Zone

1

2

3

4

5

6

7

8.7

11.6

11.6

12.0

16.0

16.0

16.0

11.0

14.7

14.7

15.2

20.3

20.3

20.3

Rating (kWh/m )

40

35

23

23

20

20

20

No. of burners (30 kW)

15

17

12 1

1

1

1

Length (m) 2

Area (m ) 2

No. of burners (350 kW) Note: Position of No. of burners (350 kW).

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FIGURE 7.19 Baker Pacific direct gas-fired/indirect radiant multipurpose oven built and installed in China.

Additional information on sources Biscuit oven manufacturers Ariete-Indu´stria e Come´rcio de Ma´quinas e Fornos R. Malmequer do Campo, 1313 Gleba do Peˆssego, Sa˜o Paulo, SP, 08265-380, Brazil Tel.: 1 55 11 3130-1450 www.ariete.com.br Baker Pacific Cambridge CB24 9YZ, United Kingdom www.bakerpacific.net S. Eldridge Design Ltd. 37 Hazelwood Close, Honiton, Devon, United Kingdom EX14 2XA Tel.: 07703 575650 www.seldridgedesign.co.uk Baker Perkins Ltd. Manor Drive, Paston Parkway, Peterborough, United Kingdom Tel.: 1 44 1733 283000 www.bakerperkins.com Dingson Food Machinery 13 Teng Yun Road, Tanzhou Town, Zhongshan City, Guangdong Province, China, 528467 Tel.: 86-760 8678 www.dsm-mc.com

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Additional information on sources

Reading Bakery Systems 380 Old West Penn Avenue, Robesonia, Pennsylvania, PA 19551, United States Phone: 1 1 610-693-5816 www.readingbakery.com

Oven band manufacturers Ashworth Inc. 450 Armour Dale Winchester, VA 22601, United States Phone: (540) 662-3494 www.ashworth.com, www.conveyorbelting.net Cambridge Engineered Solutions 105 Goodwill Road, Cambridge, MD 21613, United States Phone: 410 901 2660 www.cambridge-es.com Steinhaus GmbH Platanenallee 46, 45478 Mu¨lheim an der Ruhr, Germany Phone: 1 49 208 580101 www.steinhaus.de Weishaupt Corp. Max Weishaupt GmbH, Max-Weishaupt-Straße 1488477 Schwendi, Germany www.weishaupt-corp.com

Oven burner manufacturers Eratec. MFB Burners 80 Rue Rene Descartes, 38090 Vaulx-Millieu, France Phone: 1 33 474 821 900 www.era-tec.com Flynn Burner Corp. USA 225 Mooresville Blvd, Mooresville, NC 28115, United States Phone: 1 1 704-660-1500 www.flynnburner.com Honeywell Maxon Corp. Muncie, IN 47302, United States https://processhoneywell.com/thermalsolutions

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Heat flux technology Digitron. Thermaflux. Thermal Profile Solutions Kenfig Industrial Estate, Margam, Port Talbot SA13 2PW, United Kingdom Tel.: 1 44 (0) 1656 747 575 www.digitron.com Heat Flux Kenfig Industrial Estate, Margam, Port Talbot SA13 2PW, United Kingdom Tel.: 1 44 (0) 1656 747 575 www.digitron.co.uk Wikipedia. Heat Flux. http://en.wikipedia.org

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8 Oven construction: direct gas-fired ovens 8.1 Direct gas-fired baking chamber The following are the main considerations in specifying and constructing a direct gas-fired (DGF) baking chamber: • • • • • •

Baking chamber materials and dimensions Expansion joints Explosion relief Insulation Inspection doors Cleanout doors

8.1.1 Baking chamber construction Baker Pacific chambers are constructed in 2.9 m modules (Figs. 8.1 and 8.2).

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FIGURE 8.1 Baker Pacific DGF baking chamber installation. DGF, direct gas-fired.

FIGURE 8.2 (1) Baking chamber side, (2) burner box, (3) clean out door, (4) cover support, (5) base stiffener, (6) oven band supports.

8.1.2 Conversion of gas-fired oven to electric The DGF burners may be replaced by electric heaters. The apertures and supports are designed to accept both burners and electrical heaters (Fig. 8.3).

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FIGURE 8.3 Direct gas-fired baking chamber is designed to accept both gas burners and electric heating elements.

8.1.3 Materials Baking chambers are normally constructed from 2.5 mm mild steel. This may be coated with heat-resistant aluminium paint applied only below the oven band to ensure no paint can flake and fall onto the product. This gives added protection against corrosion. A special material may be used called ‘Aludip’, which is manufactured in the United Kingdom and available from Tata Steel. It is a mild steel sheet with an aluminium surface bonded to it at the mill. The aluminium surface gives the material high corrosion resistance. Alternatives are special steels used in the building industry. These steels weather to bronze colour and thereafter have good corrosion resistance. For crackers and biscuits with salt sprinkled on top, it is usual to construct the baking chamber of the first zone in stainless steel. It should be noted that oxidised mild steel without finishes gives the best level of radiation with an emissivity coefficient of 0.79, compared to an aluminium coating of 0.27 0.67.

8.1.4 Dimensions The baking chamber should not exceed 550 mm in height to optimise the radiation intensity from the burners and the top and bottom of the chamber. Adequate clearance on each side of the oven band is required to allow band-tracking movement and the installation of tracking rollers. Normally this dimension is 150 mm on each side of the band.

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8.1.5 Expansion joints As the baking chamber heats up and cools, it will expand and contract. To accommodate this movement, the baking chambers are allowed to slide on the base structure (Figs. 8.4 8.6).

FIGURE 8.4 Baking chamber support slide.

FIGURE 8.5 Expansion joint between two oven zones.

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FIGURE 8.6 The joints between each zone have sliding spigots to take up the expansion. (1) Male backplate, (2) male spigot, (3) female backplate and (4) female spigot.

8.1.6 Insulation The baking chamber requires adequate mineral wool insulation. This is supplied in slabs, 50, 100 and 150 mm thick and with 70 kg/m3 density up to over 140 kg/m3 density for particularly hot areas. The total thickness of the insulation should be 250 mm on top, 200 mm on the sides and 150 mm on the bottom of the baking chamber. The outer surface of the insulation uses mineral wool slabs which are covered by aluminium foil to protect them and to present a clean outer surface. Joins are covered by aluminium tape (Figs. 8.7 and 8.8).

FIGURE 8.7 Mineral wool insulation slabs.

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FIGURE 8.8 Aluminium outer surface of the insulation.

8.1.7 Oven return band covers On many DGF ovens, the return band is open and loses heat to the bakery. For cracker ovens with oven bands running at higher temperatures, the return band should be covered with insulated panels. These may be easily lifted off for access to band support rollers (Figs. 8.9 and 8.10).

FIGURE 8.9 Oven return band covers.

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FIGURE 8.10

Oven return band covers.

8.1.8 Explosion relief In DGF ovens, there is a possibility of explosion or fire caused by the ignition of unburned gas or by the product catching fire after a stoppage of the oven band and consequent overheating. To minimise the damage caused by explosion or fire, each baking chamber module has a relief panel on the top of the baking chamber. This has a thin plate, which represents the weakest part of the baking chamber and will blow out in the event of a rapid increase in pressure. The thin plate can be retained by bars or chains so that it cannot be ejected and cause injury to nearby operators (Figs. 8.11 and 8.12).

FIGURE 8.11

Explosion relief panel on the top of the oven.

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8. Oven construction: direct gas-fired ovens

FIGURE 8.12 Explosion relief. (1) Explosion relief duct, (2) retainers, (3) explosion relief panel and (4) top sheet of the baking chamber.

8.1.9 Inspection doors Each zone has an inspection door to enable the operator to check the condition of the product during the baking process. The door is provided with a lamp to view the product (Fig. 8.13).

FIGURE 8.13 Baker Pacific stainless steel inspection door. Biscuit Baking Technology

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8.1.10 Cleanout doors Doors are provided on the non-control side of the baking chamber to provide access both for cleaning the inside of the baking chamber and for access to burner supports, oven band supports and tracking rollers (Fig. 8.14).

FIGURE 8.14

Cleanout door.

Cleanout doors should provide access of at least 600 3 300 mm, and the bottom of the door should be level with the base of the baking chamber to aid the sweeping out of the debris. Cleanout doors should be provided in each module.

8.2 Extraction system Moisture from the dough pieces may be extracted from the baking chamber in each zone. The wet air in the baking chamber is drawn into a series of cross ducts at the top of the baking chamber. This wet air then enters the extraction duct running along the top of the baking chamber to the extraction fan entry. The wet air is exhausted through a

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vertical flue (chimney) to atmosphere. The amount of air extracted in each zone is controlled by a damper, which may be manually adjusted or by a motorised valve controlled by PLC (Fig. 8.15).

FIGURE 8.15 Halifax extraction fan mounted on top of DGF zone. DGF, direct gas-fired.

8.2.1 Fan specification Halifax 12P multi-vane forward curved fans (Fig. 8.16)

FIGURE 8.16

Direct gas-fired oven showing the extraction fans and combustion air

fans.

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• • • •

153

Volume: 34 m3/min Pressure: 70 mm Outlet velocity: 8.4 m/s Impeller speed: 1399 rpm

8.2.2 Extraction: oven end hood The oven band carrying baked products at the exit to the oven is at 150 C 250 C and will lose heat to the bakery. In addition, hot air from the baking chamber is drawn out at the oven end. In many cases, this area in the bakery is excessively hot. An enclosed hood with fan and flue will assist in containing this heat and exhaust it through the flue to atmosphere (Fig. 8.17).

FIGURE 8.17

Baker Pacific oven end hood with extraction fan and flue.

8.3 Direct gas-fired oven: gas burner system DGF oven burners use a ‘zero-pressure’ gas system. The burners ignite and burn a gas/air mixture. The gas is supplied to the gas/air mixer unit at nominally zero pressure. The air is supplied at a positive,

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controlled pressure. An increase in air pressure increases the flame and the heat input to the baking chamber. The gas may be natural gas, town gas (manufactured from coal) or LPG.

8.3.1 Gas train Mains gas is supplied from a factory system to the oven where it is regulated by a ‘gas train’. This consists of the following equipment: • • • • • • • •

Manual shut-off valve Two automatic shut-off valves for the safety system Gas filter Zero-pressure gas governor Gas pressure high/low detection Gas pressure gauges (2) at gas inlet and outlet of gas train Gas valve tightness proving facility (to check for a leakage of gas) Main gas pipes and gas distribution system

The gas is fed to header pipes running along each zone of the oven at the top and bottom. The headers are connected to each burner by flexible hoses and via a solenoid valve and gas/air mixer.

8.3.2 Combustion air In each zone, the air is fed to the air header pipes from an air blower mounted on top of the oven. The air is drawn from the bakery and is filtered. The air pressure for the burner system is controlled by motorised valves which are regulated by the automatic temperature control system or by a variable speed inverter drive for the fan (Figs. 8.18 and 8.19).

FIGURE 8.18 Combustion air fan mounted on top of a DGF oven. DGF, direct gas-fired.

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FIGURE 8.19 Direct gas-fired burner installation with Eratec equipment showing: gas header pipe (yellow), combustion air headers (blue), gas solenoid valves (also functioning as zero gas governors), gas/air mixers and flame managers.

8.3.3 Temperature control system In each oven zone, the temperature in the baking chamber is detected above and below the oven band by thermocouples. There are two thermocouples above and two below the band in each zone. These are connected to a controller, which averages the temperatures to provide the actual baking temperature, either a single temperature or separate temperatures for the top and bottom of the oven. The control system will automatically increase or decrease the air pressure to the burners to increase/decrease the heat input to maintain the set baking temperatures. The baking temperature should be maintained within 6 1 C (Figs. 8.20 and 8.21).

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FIGURE 8.20

8. Oven construction: direct gas-fired ovens

Baker Pacific zone control panel with temperature controllers for two

oven zones.

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FIGURE 8.21

157

Temperature controllers for two oven zones.

The Omron controllers show the set temperature and the actual temperature. There are separate controllers for the top and bottom temperatures and a pre-set controller to detect over temperature for safety.

8.3.4 Flynn burners for direct gas-fired oven DGF ovens use ‘ribbon’ burners installed above and below the oven band. A gas/air mixture is fed to the burner tube and burns on a special strip of corrugated or woven stainless steel. The gas may be natural gas, town gas (manufactured from coal) or LPG. In some cases, an alternative design of strip may be required for town gas, which has a low calorific value. The burner consists of a tube with a slot along part of its length into which are placed a number of formed stainless steel strips. This provides numerous small ports through which the gas/air mixture passes for combustion. This strip design ensures: 1. Continuous flame of uniform height 2. Good flame retention properties on high flame 3. Prevention of light back on low flame The burners installed in DGF ovens are generally of two sizes: 1v diameter pipe with a capacity of 9.9 kcal/mm (11.5 W/mm) of strip and

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2v diameter with a capacity of 24.8 kcal/mm (28.8 W/mm). These capacities are for burners up to 1220 mm long. The burners are installed in ports spaced approximately 625 825 mm apart. The burners are arranged with the strip at the side so that the flame is horizontal and is in the direction of the general airflow in the baking chamber from the feed to delivery end of the oven. The burners are ignited by spark electrodes (Figs. 8.22 8.25).

FIGURE 8.22 Burner installation with air feed, gas feed with solenoid valve, gas/air mixer and ignition.

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FIGURE 8.23

Burner strip.

FIGURE 8.24

Flynn distributor burner head (3 lane).

FIGURE 8.25

Flynn 3 lane flame adjustment.

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Multi-lane distributor burners allow the flame to be adjusted in separate lanes to balance the heat input across the width of the oven band. The Flynn burner shown above is adjustable in three lanes. On DGF ovens, it is recommended that a minimum of 15% of the burners installed are adjustable (Fig. 8.26).

FIGURE 8.26 Flynn spark monitor system for each burner. Biscuit Baking Technology

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The flame ignition is controlled at each burner by a flame manager/ spark monitor system. This solid state unit controls the electrical spark ignition and monitors the flame. The unit is equipped with on/off switch and flame indicating lights. It can be used with most existing ignition electrodes (Figs. 8.27 and 8.28).

FIGURE 8.27

MFB burners from Era-tec.

FIGURE 8.28

Metal fibre mesh from Era-tec.

8.3.5 Infrared metal fibre burners • MFB burners provide direct heat transfer by radiation (without contact and air movement) • High radiant power density 100 1000 kW/m2 • Input power from 6 to 34 kW • Precise control and power modulation. Fast heat up and cool down. • Energy consumption savings compared to conventional DGF burners • Low pollution (up to 80% less CO and NOx)

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• Cylindrical infrared burner in knitted FecralloyR Nit200S from Bekaert • Length of IR surface: 1000 1500 mm • Casing: tube stainless steel 304 2 mm to 60.3 mm diametre • Input power adjustment by air pressure from 20 to 80 mbar • Gas pressure 0 bar • Available with multi-lane adjustment

8.3.6 Flynn infrared profile 7 distributor burner • • • • • •

High combustion efficiency with homogeneous premixing Low pollutant (CO2, NOx) with less excess air Enable compact design with a slim combustion chamber Fast heat up and cool down Reach target temperature with 5 s and cool down within 1 s Flynn rating for woven IR material: 268 kW/m2 of mesh (Fig. 8.29)

FIGURE 8.29 Flynn infrared profile distributer burner.

8.4 Control panels 8.4.1 Main control panels These panels, located at the end of the oven, will contain all the controls and displays for the conveyor drive, band cleaner, oven band tracking and tension, burners off/on and purge cycle, together with safety alarms (Figs. 8.30 and 8.31).

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8.4 Control panels

FIGURE 8.30

Main control panel fascia.

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FIGURE 8.31 Zone panel for separate top and bottom burner control.

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8.4.2 Control panel construction The industry standard is Rittal, Friedhelm LOH Group. Many local manufacturers build panels to the Rittal standard specifications. Protection is IP55 to EN 60 52 standards and complies with NEMA 12 (Fig. 8.32).

FIGURE 8.32

Rittall type control panel.

Modern cable trunking is open to prevent infestation and allow inspection and repair/modification (Fig. 8.33).

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FIGURE 8.33 Main trunking from panel and along the oven.

Further reading Baker Pacific., Cambridge CB24 9YZ, United Kingdom. www.bakerpacific.net Eratec France., 80 rue Rene´ Descartes, 38090, Vaulx-Milieu, France. www.era-tec.com Flynn Burner Corp., 225 Mooresville Blvd, Mooresville, NC 28115, USA. www.flynnburner.com Halifax Fan. Unit 11, Brookfoot Business Park, Elland Rd, Brighouse HD6 2SD, United Kingdom. www.halifax-fan.co.uk Moro Srl., Via Pirandello, Barssalina, MB, Italy. www.ventilatori-industriali.eu Omron, Kyoto, Japan. www.omron.com Rittal Gmbh & Co. KG, Auf dem Stu¨tzelberg, D-35745 Herborn, Germany. www.rittal.com Rockwool A/S, Hovedgaden 584, DK-2640, Hedehusene, Denmark. www.rockwool.com S. Eldridge Design Ltd., 37 Hazelwood Close, Honiton, Devon EX14 2XA, United Kingdom. www.seldridgedesign.co.uk Selas Heat Technology Co., 11012 Aurora Hudson Road, Streetsboro, OH 44241 USA. www.selas.com

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C H A P T E R

9 Oven construction: indirect radiant ovens 9.1 Indirect radiant baking chamber The following are the main considerations in specifying and installing indirect radiant baking chambers. • • • • • • • • •

Baking chamber construction and dimensions Expansion joints Heater module Radiant tubes and ducts Extraction system Explosion relief Insulation Inspection doors Cleanout doors.

9.1.1 Baking chamber construction and dimensions The baking chambers are constructed in modules, normally 2.3 m long. Each zone has a single heater module with a burner and combustion chamber. Materials for the baking chamber are mild steel 3.0 mm thick (Figs. 9.1 9.3).

FIGURE 9.1 Plan of zone layout for Baker Pacific radiant oven.

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FIGURE 9.2 Baker Pacific indirect radiant oven: installation of combustion chambers and zone end headers.

FIGURE 9.3 Installation of heater modules and baking chambers.

The baking chambers should be a minimum height (not exceeding 710 mm), and the radiant tubes should be no more than 215 mm from the band (top) and 165 mm (bottom) to ensure the maximum intensity of radiation to the product. To ensure the radiant tubes are close to the oven band, the turbulence ducts are situated above and below the baking chamber (Fig. 9.4).

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710 mm

215 mm 165 mm

FIGURE 9.4 Section diagram for indirect radiant oven showing the position of the radiant tubes and the turbulence system ducts located at the top and bottom of the oven.

9.1.2 Expansion joints Expansion joints are located between each zone to allow expansion and contraction of the baking chambers. These take the form of either stainless steel bellows, which open and close as the temperature of the baking chambers changes or a sliding male and female joint (Figs. 9.5 and 9.6).

FIGURE 9.5 Bellows type.

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FIGURE 9.6 Sliding male/female spigot type.

9.1.3 Heater module Each zone has a single burner. The burner fires into a stainless steel burner tube from where the hot gases enter a vertical duct at the back of the oven and are distributed to cross ducts at the top and bottom of the oven. From the cross ducts, the gases enter the radiant tubes (Figs. 9.7 9.9).

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FIGURE 9.7 Heater module showing burner tube and distribution cross ducts to the radiant tubes with adjustable plates for balancing lateral heat transfer.

FIGURE 9.8 Heater module showing burner tube and distribution cross ducts to the radiant tubes with adjustable plates for balancing lateral heat transfer.

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FIGURE 9.9 (1) Burner, (2) burner mounting plate, (3) burner tube, (4) burner tail tube and (5) outer tube.

At the entry of the flue gases to the radiant tubes in the distribution ducts, sliding plates with adjustable blanking discs for each tube are located. These allow the heat distribution across the width of the oven to be balanced during commissioning. This facility enables the oven to achieve good lateral control of the baking across the width of the oven.

9.1.4 Radiant tubes Radiant tubes are manufactured from 4v (101.6 mm) diameter mild steel tube. They are arranged along each zone with an offset so that they do not run parallel to the direction of the band. This avoids the radiation from each tube to the products being applied in parallel stripes along the length of the oven zone (Figs. 9.10 9.12).

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9.1 Indirect radiant baking chamber

FIGURE 9.10

Radiant tubes.

FIGURE 9.11

Radiant tubes.

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9. Oven construction: indirect radiant ovens

FIGURE 9.12 Section of the baking chamber. Note the offset of the radiant tubes.

The distance between the tubes and the oven band and the pitch of the tubes is important in maximising the radiation intensity. Baker Pacific radiant tubes have a pitch of 145 mm.

9.1.5 Return ducts At the end of the zone, the hot gases enter header ducts from where they are drawn through a return duct above the baking chamber, returning to the circulation fan (Fig. 9.13).

FIGURE 9.13 Arrangement of an indirect radiant zone. Source: Drawing courtesy of Esspee Engineers.

9.1.6 Circulation fan The fan is located next to the burner. The fan draws the hot gases through the system, distribution ducts, radiant tubes, headers and return ducts and circulates the hot air back to the burner tube. Note that the radiant heating system is under negative pressure, which ensures

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that the products of combustion do not leak into the baking chamber (Fig. 9.14).

FIGURE 9.14

Halifax circulation fan.

Specification of the circulation fan for 1.25 m wide oven: Halifax Fan 18P Multi-vane Forward Curved Fan Volume: 170 m3/min Pressure: 50 mm/30 mm WG

9.1.7 Extraction and turbulence In each zone, a duct above the band extracts a proportion of the moist air to the extraction fan. From the fan the moist air enters a duct at the side of the oven where it may be directed to the turbulence duct or to the flue to the atmosphere. The system is controlled by dampers (Fig. 9.15).

Biscuit Baking Technology

FIGURE 9.15 Halifax extraction fan.

Specification of extraction fan for 1.25 m wide oven: Halifax Fan 15P Multi-vane Forward Curved Fan Volume: 114 m3/min Pressure: 70 mm WG at 20 C The hot air from the baking chamber is extracted by the fan. It enters a duct above the fan and from there to the turbulence ducts for top and bottom turbulence, or it can be exhausted into the atmosphere through the flue on the left. The damper positions are shown: the damper on the left controls the extraction to the atmosphere and the two dampers on the right control the top and bottom turbulence system (Fig. 9.16).

FIGURE 9.16 Extraction and turbulence ducts.

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9.1.8 Heat exchanger flue (chimney) During operation the burner is drawing in air for combustion. To relieve the pressure in the system, a flue with natural convection is arranged between the circulating fan and the burner tube. This flue allows hot air and burnt gas to escape and maintains negative pressure in the circulating system. The heat exchanger flue is on the right in the picture above. This hot air and gas is relatively dry and is usually over 200 C. This hot air is used in the heat recovery system.

9.1.9 Explosion relief In an indirect system, the risk of explosion is confined to the closed heating system. An explosion relief panel is located in the vertical duct opposite to the burner (Fig. 9.17).

FIGURE 9.17

Back of heater module with cover removed to show position for explo-

sion relief panel.

9.1.10 Insulation The insulation is similar to that used for the direct gas-fired ovens. Mineral wool slabs are used of 50, 100 and 150 mm thick and with 70 kg/m3 density (standard) and up to over 140 kg/m3 density for particularly hot areas. High-temperature areas around the burner tube may be insulated by high-temperature thermal ceramics, for example, Morgan Superwool Plus, with density 128 kg/m3, which has excellent performance up to 1000 C.

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9.1.11 Inspection doors An inspection door with a lamp is located in each zone (Fig. 9.18).

FIGURE 9.18 Inspection door.

9.1.12 Cleanout doors Cleanout doors are located at the back of the oven to give access to the baking chamber. These are ‘plug’ doors which can be pulled out to give access for cleaning the baking chamber (Figs. 9.19 and 9.20).

FIGURE 9.19 Large insulated cleanout doors are located in each baking chamber module behind the outer covers. Biscuit Baking Technology

FIGURE 9.20 Large insulated cleanout doors are located in each baking chamber module behind the outer covers.

9.2 Indirect fired ovens: burners 9.2.1 Weishaupt burners 9.2.1.1 Technical description The Weishaupt WG burner is a forced draught gas burner. For biscuit oven applications, the burner should always be a fully modulating type. The burner comprises the following features (Fig. 9.21):

FIGURE 9.21

Baker Pacific indirect radiant oven with Weishaupt WG burner installation.

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1. Combustion manager • Microprocessor control and monitoring of all burner functions • LCD display • Keypad operation • Data bus connection • Integrated valve proving of the solenoid valves 2. Flame sensor • Monitors the flame during operation. If a problem occurs, a safety lockout will operate. 3. Double solenoid valve • Gas pressure governor. Controlled pressure is set by an adjusting screw • Air/gas ratio control provides optimisation over control range • Two solenoid (Class A) valves • Gas filter 4. Low gas pressure switch 5. Gas pressure switch for automatic valve proving 6. Air pressure switch • Loss of combustion air pressure activates a safety shut down (Figs. 9.22 9.24) 7. Weishaupt gas train

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9.2 Indirect fired ovens: burners

FIGURE 9.22

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Weishaupt WG burner. Source: Picture courtesy of Max Weishaupt GmbH.

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FIGURE 9.23 Baker Pacific oven with Weishaupt burner and gas train for natural gas.

FIGURE 9.24 Gas valve trains.

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9.2.1.2 Specification: Weishaupt burner WG30N/1-C ZM LN (for 1.25 m wide indirect radiant oven) • Version: modulating via three term switching and Buyer’s PID controller • Fuel: natural gas • Gas pressure: 30 mbar • Rating capacity: 40 350 kW • Electro motor: 1 ph, 0.42 kW, 230 V, 50 Hz • Combustion manager: Siemens Type W-FM20 • Flame monitor • Continuous running fan • Gas valve train size 1v • Double magnetic valve (DMV) • Gas pressure switch • Gas pressure regulator assembly with safety valve • Gas pressure inlet: (maximum) 2.5 bar • Gas pressure outlet: 20 mbar • Gas filter • Gas ball valve • Fitting, reducing and sealing parts.

9.2.2 Maxon burners Refer Figs. 9.25 and 9.26.

FIGURE 9.25 Maxon OVENPAK 515SP burners complete with gas feed trains and oil feed and compressed air trains.

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FIGURE 9.26 Baker Pacific oven with Maxon OVENPAK 515SP dual fuel burner assembly.

9.2.2.1 Specification for 1.2 m wide indirect radiant oven 9.2.2.1.1 Maxon OVENPAK 515 gas/oil burner

• • • • •

Maximum heat release: 1,250,000 Btu/h (366 kW) Minimum heat release: 77,000 Btu/h (22.5 kW) Oil pressure required: 60 psig (4.13 bar) Natural gas pressure: 2.0 bar (to be reduced to 0.005 bar) Compressed air required: 60 psig (4.13 bar). Each burner is complete with:

• • • • • • •

Pilot adjustable orifice UV sensor device Dual-type nozzle for oil/gas operation Integral combustion air blower Servo motor Ignition transformer Air pressure switch.

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9.2.2.1.2 Maxon gas pipe trains

• • • • • • • • •

Gas strainer Gas cock Main gas regulator, size 1.25v Pressure gauge for upstream (0 30 psig) Pressure gauge for downstream (0 15v WG) Low-pressure switch (0.5 4v WG) High-pressure switch (5 28v WG) Maxon solenoid valve series 5000 Solenoid valve.

9.2.2.1.3 Pilot gas train

• • • • •

Pilot regulator: high-pressure regulator Pilot solenoid: general-purpose type Pressure switch for pilot Outlet pressure gauge Locking ball valve.

9.2.2.1.4 Oil pipe train

• • • • • • •

Oil filter, size 3/8v Oil pressure regulator, size 3/8v Low-pressure switch High-pressure switch Solenoid valve for burner Locking ball valve Fuel: diesel oil.

9.2.2.1.5 Compressed air train

• • • •

Air filter Air pressure regulator Air pressure switch for low air pressure Solenoid valve for burner.

Further reading Baker Pacific Ltd, 2021. Cambridge CB249YZ, United Kingdom. http://www.bakerpacific.net. Baker Perkins Ltd, 2021. Manor Drive, Paston Parkway, Peterborough, PE4 7AP, United Kingdom. http://www.bakerperkins.com. Buhler AG, 2021. Gupfenstrasse 5. CH-9240 Uzwil, Switzerland. http://www.buhlergroup.com. Espee Engineers, 2021. Malegaon Industrial Area, Malegaon, Maharashtra 422113, India. http://www.espenger.com.

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Halifax Fan Ltd, 2021. Unit 11, Brookfoot Business Park, Elland Rd, Brighouse, HD6 2SD, United Kingdom. http://www.halifax-fan.com. S. Eldridge Design Ltd, 2021. 37 Hazelwood Cl, Honiton EX14 2XA, United Kingdom. http://www.seldridgedesign.co.uk. Honeywell Thermal Solutions. https://process.honeywell.com. Morgan Advanced Materials. York House, Sheet Street, Windsor, SL4 1DD, United Kingdom http://www.morganthermalceramics.com. Weishaupt, 2021. Max-Weishaupt-Straße 14, 88477 Schwendi, Germany. http://www. weishaupt.co.uk.

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C H A P T E R

10 Heat recovery system 10.1 Heat recovery system The heat recovery system (HRS) uses the waste heat from the burner flues. This may be used to heat one or two final zones of the oven. These zones would not require burners, giving a saving in capital and running costs. All gas burners draw in a large amount of air for combustion. For complete combustion, 1.0 m3 of gas requires 3.0 m3 of oxygen (approximately 15 m3 of air). Excess combustion air improves efficiency. This air is exhausted through the extraction system of a direct gas-fired oven and through the natural draught burner flue of an indirect-fired oven. The hot air and burnt gas in the burner flues of an indirect radiant oven are at a high temperature, typically over 200
C, and this hot air can be recovered and used for baking in a HRS. A proportion of the hot gases in the burner flues are diverted to a HRS collection pipe which runs along the top of the oven. Hot flue gases are collected from each zone with a burner. The hot flue gases are drawn along the collection pipe by a fan and blown into radiant or convection ducts in the heat recovery zone (Figs. 10.110.3).

FIGURE 10.1

Baker Pacific indirect radiant oven with heat recovery system.

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FIGURE 10.2 Layout drawing of the heat recovery system.

FIGURE 10.3 Indirect radiant oven with heat recovery zone showing the burner flues and collection pipe.

The burner flue (on the right) is connected to the HRS collection pipe, and the flow of hot gases is controlled by dampers (Fig. 10.4). One

FIGURE 10.4 Burner flue connected to the collection pipe.

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damper controls the quantity of flue gas to the exhaust flue, and another damper controls the quantity of flue gas to the connecting pipe for the HRS. These dampers are set by the commissioning engineer to allow a sufficient quantity of heat for the heat recovery zone. The HRS zone is constructed with ducts above and below the oven band. The hot gases recovered from the burner flues are fed by the fan to the ducts. The fan is located on top of the oven at the end of the collection pipe (Figs. 10.5 and 10.6).

FIGURE 10.5

Heat recovery zone.

FIGURE 10.6

Heat recovery zone.

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10. Heat recovery system

The final zone of the oven has radiant or convection ducts above and below the oven band. These ducts are divided along their length into three sections (control side, centre and non-control side) (Fig. 10.7). The

FIGURE 10.7 Controls for top and bottom ducts (control side, centre and non-control side).

flow of hot flue gas into each section is controlled by a damper. These dampers may be adjusted to ensure the optimum heat balance from top to bottom and across the width of the oven (Fig. 10.8).

FIGURE 10.8 Heat recovery zone with radiant ducts. Biscuit Baking Technology

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The heat recovery zone may also be designed as a convection zone. This is particularly beneficial for products requiring an even bland colour and even low moisture content (Fig. 10.9).

FIGURE 10.9

Heat recovery zone with convection system.

10.1.1 Calculations of hot air flow to the HRS zone Calculations are based on the following oven specification: • • • • •

1.2 m 3 100 m indirect radiant oven 8 zones/7 burners 3 350 kW/1 HRS zone Product: Rotary moulded Output: 3200 kg/h Energy used: 0.4043 kWh/kg

Total energy used per hour: 0.4043 kWh 3 3200 5 1294 kWh Natural gas energy: 10.3 kWh/m3 Gas consumption per hour 5 1294/10.3 m3 5 125 m3 For the combustion of 1 m3 of natural gas, 9.411.0 m3 (average 10.2 m3) of air is required. Air volume required per hour for complete combustion is approximately 125 3 10.2 m3/h 5 1275 m3

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10. Heat recovery system

The total volume of products of combustion exhausted is approximately 1400 m3/h This is the total volume of hot burnt gas/air available for HRS. If we assume that the temperature of the hot air delivered to the final zone is 200
C (170
C above ambient), the density and specific weight are given below (Figs. 10.10 and 10.11):

FIGURE 10.10 Air density and specific weight.

FIGURE 10.11 Heat recovery zone on a Baker Pacific indirect radiant oven.

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The energy available in the HRS zone can be calculated as follows:

EnergyðkWhÞ 5 air volume m3 =h 3 density of air at 200
C 0:75 kg=m3
3 specific heat 0:000285 kWh=kg
C 3 temperature above ambientð
CÞ Energy 5 1400 3 0:75 3 0:000285 3 170 5 50:9kWh The oven shown above is 1.2 m 3 100 m with seven burners. The HRS has two zones without burners.

Further reading Baker Pacific Ltd, 2021. Cambridge CB24 9YZ, United Kingdom. http://www.bakerpacific.net. Esspee Engineers, 2021. Kolkata, India. http://www.espenger.com. S. Eldridge Design Ltd, 2021. 37 Hazelwood Cl, Honiton EX14 2XA, United Kingdom. http://www.seldridgedesign.co.uk. Sage, 2021. Sage Metering Co. http://www.sagemetering.com. The Engineering ToolBox, 2021. Air Heating Systems. http://www.engineeringtoolbox.com.

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C H A P T E R

11 Oven construction: convection ovens 11.1 Direct and indirect convection systems Convection ovens bake by impinging hot air jets onto the products and conveyor from above and below. For most products, the first third of the oven zones requires heat transfer by radiation with minimum convection so that the product structure and volume are developed. Convection zones are effective in reducing moisture contents and developing colour in the middle and final oven zones of hybrid ovens. For products such as Danish Butter Cookies, where the product size and shape are determined by the moulding and depositing equipment and change little during baking, convection ovens are used. The convection ovens may be direct- or indirect-fired. The indirectfired ovens have a heat exchanger that can use gas or diesel fuel as the products of combustion do not enter the baking chamber. Direct convection ovens have a much faster temperature response time and a high turndown ratio of 40:1. Direct convection ovens provide significant savings in fuel cost and maintenance compared to indirect convection ovens (Figs. 11.1 and 11.2).

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FIGURE 11.1 Baker Perkins TruBake HiCirc Convection oven.

FIGURE 11.2 Baker Perkins oven module with burner and inspection door.

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11.2 Baking chamber The main considerations for the baking chamber for a convection oven are: • Baking chamber construction • Plenums to deliver convective air • Heating system

11.2.1 Baking chamber construction Baking chambers are constructed in complete modules, approximately 2.0 m long. The baking chamber is constructed in mild steel. This may be an Aludip material with an aluminium surface to reduce corrosion. Typical height of the chamber will be 1250 mm, accommodating convection plenums above and below the oven band (Fig. 11.3).

FIGURE 11.3 Baker Perkins baking chamber TruBake HiCirc Convection oven.

11.2.2 Convection plenums The heated air from the burner module is blown by the circulation system into plenums above and below the oven band. The convection plenums will have slots or holes to direct the heated convective air onto the top and bottom of the conveyor and the dough pieces. The heated air will impinge directly onto the dough pieces from above and through an open mesh oven band from below (Fig. 11.4).

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FIGURE 11.4 Convective airflow to top convection plenum.

11.2.3 Return air The convective air entering the baking chamber from the plenums is then drawn into collection ducts and returned to the burner module. It is important that the system maintains a stable and even air movement across the width of the oven and along the length of the zone. Variations in airflow will lead to uneven baking, colour, moisture content and product weight variation. In the Baker Perkins TruBake HiCirc oven, the heated air blown from the plenums is returned to the burner module by a controlled system through ducts at each side and the top and bottom of the baking chamber. This system results in a more even and stable movement of air in the baking chamber and gives consistent product quality (Fig. 11.5).

FIGURE 11.5 Baker Perkins TruBake HiCirc oven showing return airflow.

11.2.4 Circulation fan The volume and velocity of the heated air are important. Higher volume and velocity will allow the baking to be achieved at a lower

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temperature, thereby improving fuel efficiency. This is enhanced by a return system that quickly removes spent air from the baking surface and prevents slowing of heat transfer to the product.

11.2.5 Heater module The view of heater module with Maxon burner is shown in Figs. 11.6 and 11.7.

FIGURE 11.6

Direct heater module with Maxon burner.

FIGURE 11.7

Maxon burner.

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Further reading Baker Perkins Ltd., 2021. Manor Drive, Paston Parkway, Peterborough, PE4 7AP United Kingdom. www.bakerperkins.com. Honeywell Maxon, 2021. Honeywell Thermal Solutions. https://process.honeywell.com.

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C H A P T E R

12 Oven construction: electric ovens 12.1 Electric oven construction The directly heated electric oven bakes by radiant heat from electric elements above and below the oven band in the baking chamber. The construction of the oven baking chambers is similar to the direct gasfired oven (Figs. 12.1 12.3).

FIGURE 12.1

Electric oven from Laser srl Italy.

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FIGURE 12.2 Electric oven from Laser srl Italy.

FIGURE 12.3 Electric oven from Laser srl Italy.

12.2 Electrical elements The Baker Pacific electric oven design employs heater units installed in each module of the oven. The electric elements are mounted in frames which can be slid into or dropped into the baking chambers.

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12.2 Electrical elements

The tubular elements provide radiant heat to the products, the oven band and the baking chamber. The temperature range is up to more than 500 C (Fig. 12.4).

472 416

1890

1501

200

FIGURE 12.4

DhE Thermowatt electric heater.

The electric heaters shown above have a heat rating of 19.5 kW and can be installed in frames above and below the oven band to achieve a heat rating of 35.8 kW/m2 of oven band on a 1.5-m wide oven (Figs. 12.5 and 12.6).

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FIGURE 12.5 Electrical heater units installed in an oven module.

FIGURE 12.6 Electric oven from GEA Imaforni, Italy.

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12.3 Conversion of direct gas-fired oven to electrically heated oven The Baker Pacific DGF oven baking chamber has been designed for conversion from a gas-fired oven to an electric oven. As concern over the use of fossil fuels increases and the cost of electricity from renewable sources decreases, the capability to convert the oven will become valuable. The Baker Pacific DGF oven is designed for the electrical elements and the gas burners to be interchangeable. They are mounted on frames and may be slid into the baking chambers (Fig. 12.7).

FIGURE 12.7 Baker Pacific baking chamber showing interchangeable electric elements and DGF burner.

12.4 Oven efficiency Electric ovens provide high efficiency and low maintenance. • Combustion air is not required for the burners, so only the moisture from the dough pieces is extracted. The heat loss from the extraction system is greatly reduced. • Electric heating elements can be placed close to the products and oven band improving the radiant heat transfer. • Electric ovens require low maintenance compared to gas-fired ovens.

12.5 Ovens with hot air circulation There are two types of oven which apply heat from an air circulation system, namely indirect radiant (or cyclotherm) ovens and convection

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ovens. Both ovens are commonly heated by draught tube gas burners, for example, the Weishaupt WG30 or Maxon OVENPAK burner. The heated air for circulation is typically at 250 C 320 C. These gas burners could be replaced by electric duct air heaters (Fig. 12.8).

FIGURE 12.8 Watlow duct air heater.

12.5.1 Indirect radiant oven The indirect radiant ovens (also known as ‘cyclotherm’ ovens) are constructed in separate zones. Each zone is typically 10 20 m long and has a heater and circulating fan. The fan circulates the air through a duct heater with a heating capacity of up to 320 C. The heated air is drawn through ducts to rows of steel tubes, or ducts, at the top and bottom of the baking chamber. These tubes or ducts radiate heat to the products from above and below. At each end of the zone, the heated air is collected in a return duct through which they travel back to the circulating fan and from there to the duct air heater to be re-circulated. It is essentially a closed, circulating system (Fig. 12.9).

FIGURE 12.9 Indirect-fired radiant heating system.

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12.5.2 Convection ovens Convection ovens are constructed in zones, each zone having a single heater and circulation fan. The fan blows the air through the duct air heater and then through the ducts along the length of the zone. These ducts, located above and below the baking band, have slots or nozzles through which jets of hot air are blown onto the products and the oven band. Hot air from the baking chamber is drawn back to the fan to be re-circulated through the system. Each zone has an extraction fan and flue to remove moisture from the baking chamber. Convection ovens generally have fixed speed fans. Typically, the discharge velocity of the air from the nozzles is a maximum of approximately 20 m/s at a maximum temperature of 310 C 320 C. The control of the baking process is therefore by temperature by modulating the electric duct air heater and adjusting the proportion of convective air diverted to the top or bottom ducts. The airflow to the top and bottom of the oven is controlled by separate top and bottom manual or motorised dampers (Fig. 12.10).

FIGURE 12.10

Direct convection baking system.

12.6 Control systems PLC control systems provide complete process control for electric ovens. The systems have graphical user interfaces for accurate temperature PID control, data logger, baking profiles and alarms. Control systems modulate from 0% to 100% (Figs. 12.11 and 12.12).

Biscuit Baking Technology

FIGURE 12.11 Watlow F4T data logger http://www.watlow.com.

FIGURE 12.12 Watlow SpecView SCADA Software.

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Watlow equipment for both electric and gas-fired ovens. The Watlow F4T all-in-one optional capabilities include: integrated PID controller, data logger with encrypted files, graphical trend charts, limit controller, solid-state relays, timers, counters, PLC math and logic, panel switches and lights (soft keys) all connected.

Further reading Baker Pacific, Cambridge CB24 9YZ, United Kingdom. www.bakerpacific.net. DhE, Thermowatt, Via S, Giovanni Batista 21, Arceva (AN), Italy. www.dhesrl.com; www. thermowatt.com. GEA Imaforni, Via Stra`, 158, 37030 Colognola ai Colli VR, Italy. https://www.gea.com . food . bakery>. Laser Srl, Via Saturno 36, 37059 Santa Maria di Zevio, Verona, Italy. www.laserbiscuit. com. Wattco. https://www.wattco.com. Watlow, St. Louis Missouri, USA. www.watlow.com.

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C H A P T E R

13 Oven conveyor bands (belts) There are four major types of oven conveyor band for conveying the dough pieces through the oven. Each type of band has particular baking characteristics in terms of heat transfer and physical performance and therefore has a particular range of applications for biscuits, cookies and crackers.

13.1 Rolled wire-mesh bands (belts) These are the most versatile and widely used oven bands. They are suitable for crackers, semi-sweet biscuits and rotary moulded products, in fact all types of biscuits except soft cookies with high fat and sugar contents, where the dough will flow into the holes in the mesh. The wire-mesh bands conduct heat to the products and allow convective air to pass through to heat the base of the dough pieces (Fig. 13.1).

FIGURE 13.1

Rolled wire-mesh band from Steinhaus GmbH.

These wire-mesh bands, known as Z-belts, are made from carbon steel wire coils which are linked together without crossbars. The links

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give a flat surface to the band and good flexibility. Alternative materials are available for special applications, for example, stainless steel wiremesh bands may be used where the baking process has very high humidity for products such as cheesecake. The most popular bands are often referred to as Z47 and Z47R. These bands have a lower weight than belts with crossbars and have a good ratio of ‘holes to wires’ allowing air circulation through the band. The Z bands have a smooth, flat surface, but must be manufactured to give a regular and even structure to absorb the tensioning force and run straight and track well. The trend to wider and longer ovens, 1500 mm wide and up to 1800 mm wide bands and 100 m long ovens requires high quality in the manufacture of the mesh to ensure flatness and even tracking. Long ovens require sections of the wire-mesh band to be joined, and this requires accuracy in the width and dimensions of the coils in each section.

13.1.1 Z-type bands There are two types of Z band manufactured in Europe, distinguished by the belt edge, either looped or welded. These bands are manufactured by: Produits Trefiles de la Bridoire (Agrati Group). Z bands with looped edges. Steinhaus GmbH. Z bands with welded edges (Figs. 13.2 13.4)

FIGURE 13.2 F 4102 band from Steinhaus GmbH. Wire thickness 1.2 mm.

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13.1 Rolled wire-mesh bands (belts)

FIGURE 13.3

Z47 band from Agrati La Bridoire. Wire thickness 1.2 mm.

FIGURE 13.4

Ashworth U66 belt.

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Rolled oven bands widely used in the United States have crossbars.

13.1.2 Wire-mesh bands: skid bar supports Wire-mesh bands are successfully supported in the baking chamber by cast iron skid bars. These bars are placed inside the baking chamber with a pitch of 0.8 1.2 m. They are supported in frames and are removable for cleaning. Apart from cleaning, which is infrequent (normally annually), skid bars do not require any maintenance (Fig. 13.5).

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FIGURE 13.5 IPCO graphite and cast iron skid bars.

The skid bars are cast from iron with a graphite content which reduces friction. The material and casting are critical to the performance, and the skid bars are supplied to specifications, for example, International ISO/DIS 185 Grade 200/250. The chemical composition, casting process, shape of the mould and cooling rate are important to achieve the optimum low friction and durability of the skid bars in operation. The surface of the skid bar has a microstructure of a pearlitic matrix with evenly spread type A graphite flakes to ASTM A247 standard with no hard particles. Maximum allowed amount of ferrite is 10%. No ledeburite is allowed. The sliding surface of the skid bar is machined after casting by removing the surface layer (1.0 mm), which contains ferrite and would result in scratching of the band. The final surface should have a roughness of Rmax 3.0 µm. The installation of the skid bars is critical to good band tracking. The bars must be level and at right angles to the direction of band travel. Levelling is best done optically with a laser instrument (Fig. 13.6).

Biscuit Baking Technology

13.1 Rolled wire-mesh bands (belts)

FIGURE 13.6

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Baker Pacific skid bar support with levelling adjustment.

13.1.3 Wire-mesh bands: support rollers On longer ovens, rollers are often preferred to skid bars. They are installed at 1.0 1.5 m pitch along the oven. The design of the supports and adjustment for levelling and the specification of the bearings are critical as the rollers operate at baking temperatures. If the rollers seize, they will quickly cause wear to the oven band. The ends of the rollers are therefore exposed for inspection, and high-temperature bearings must be used. The bearings are mounted outside the baking chamber and are insulated from the chamber (Fig. 13.7).

FIGURE 13.7

Band support roller bearing assembly.

13.1.4 Return band supports On the return below the baking chamber, the band is supported on rollers. A proportion of these, usually one in three, may have spring-loaded

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guide discs. These are effective in keeping the band in its central position (Fig. 13.8).

FIGURE 13.8 Baker Pacific return band support roller with spring-loaded guides.

13.1.5 Wire-mesh oven band cleaning Oven band cleaning is critical to the quality of the biscuit and the oven performance. A band cleaner which operates all the time during baking is recommended, ensuring that there is no build-up of carbon, which is difficult to remove. The Baker Pacific oven band cleaner consists of two independently driven wire brushes for cleaning both sides of the band. The unit is designed for a continuous, gentle cleaning action to maintain the band in good condition. The top wire brush, driven by a fixed speed motor gearbox cleans the inside of the oven band. The lower wire brush unit cleans the outside of the oven band. The cleaner is mounted on a trolley for removal to the side of the oven. Guide rails are provided for the trolley with stops and locking handle. The brush is raised or lowered to the working position by a lever, and the brush pressure is adjustable (Fig. 13.9).

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13.1 Rolled wire-mesh bands (belts)

FIGURE 13.9

217

Baker Pacific oven band cleaner.

Maintaining a clean band is important, particularly when baking products with sugar topping. When baking products with toppings, a good system of recovery for surplus toppings is essential to prevent toppings dropping on the oven band. A long wire-mesh panning conveyor is recommended with a level transfer of the dough pieces to the oven band. The panning web should be an open-mesh band (enrober wire-mesh) and be around 2 3 m long. The end transfer roller or nosepiece is of small diameter to allow a level transfer of dough pieces to the oven band. For wire-mesh bands which have become dirty, some hard carbon deposits may be removed by heating the band to 400 C, when the hard carbon deposits will break and can be removed by the brushes. It is important that the band is heated evenly and only sufficient temperature to carbonise the debris is used. Uneven or excess heating will distort the band. Soft deposits may be removed by steam cleaning with an industrial cleaning fluid. Suitable drainage is required. After cleaning, the band should be dried and oil (soybean oil/coconut oil) applied to prevent rusting (Fig. 13.10).

FIGURE 13.10

Steinhaus CLEAN BELT. Biscuit Baking Technology

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For a good quality rolled oven band, the mesh will be regular with equal number of spirals along its length. The CLEANBELT will break the baked deposits in the mesh and enable the cleaning brushes to work more effectively.

13.1.6 Wire-mesh oven band tracking The oven installation is critical. The oven feed end drum, delivery end drum and oven baking chambers must be accurately and correctly in line. The drums and the support skid bars or rollers must be at right angles to the direction of travel of the band and be level, so that the band is in contact with the skid bar or roller across the width of the band. Drum diameter is important, and larger drums give better drive and tracking, For all but the smaller ovens, 900 1100 diameter is recommended. Baking temperatures also have an effect on tracking. At higher temperatures, the oven band elongates and will be more sensitive to tracking problems. Even temperature across the width of the band is also important. In Baker Pacific ovens, the position of the oven band edge is constantly monitored by vertical rollers on each side. The rollers are supported on a bar which follows the movement of the band. The bar carries a Euchner trip rail which engages a multiple limit switch. If the band moves up to 10 mm, it will automatically actuate a pneumatic cylinder which moves a tracking roller below the band. The oven band will always try to leave a support roller at 90 degrees to its angle. Therefore by altering the angle of the tracking roller, the band is pushed back to its central position. If the band moves more than 25 mm, then the drive will automatically stop. These settings are adjustable (Figs. 13.11 13.15).

FIGURE 13.11

Euchner trip rail and limit switch with pneumatically operated tracking

roll.

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FIGURE 13.12

Baker Pacific auto tracker assembly.

FIGURE 13.13

Band tracker at delivery end of oven.

FIGURE 13.14

Ashworth guide rollers.

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13. Oven conveyor bands (belts)

FIGURE 13.15 Ashworth guide rollers.

The tracking assemblies are mounted just before each end drum to guide the band onto the drum in a central position. The delivery end tracker is on the top, and the feed end tracker is on the return band at the bottom of the oven. The trackers may have several rolls on a single frame operating together. For heavier bands such as Ashworth U66 with crossbars, vertical guide rollers may also be used inside the baking chamber. Typically there is one assembly in each oven zone adjacent to the inspection door. These rollers are pivoted and may be spring-loaded.

13.1.7 Joining wire-mesh bands To join the ends of a wire-mesh band, two spiral joining wires are used. These are inserted from the side of the band. After insertion, the spiral joining wires are hammered flat to provide a secure and almost invisible joint (Figs. 13.16 13.18).

Biscuit Baking Technology

FIGURE 13.16

Inserting a spiral joining wire. Source: Pictures from Steinhaus GmbH.

FIGURE 13.17

Flattening the joint. Source: Pictures from Steinhaus GmbH.

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FIGURE 13.18 The final joint is almost invisible. Source: Pictures from Steinhaus GmbH.

13.1.8 Dimensions of rolled wire-mesh belts The dimensions of rolled oven belts are given in Table 13.1. TABLE 13.1

Rolled oven belts. Z 47

Z 47R

Wire diameter (mm)

1.2

1.5

Mesh opening (mm)

4.0

4.0

Belt thickness

2.1 2.2

2.7 2.8

7.0 7.4

10.0 11.2

2

Weight/m

13.2 Compound balanced weave bands These are tightly woven bands with a ‘herring bone’ pattern presenting a continuous flat surface. They are relatively heavy and have a high heat mass. These bands are pre-heated and will conduct heat directly into the base of the dough pieces. They are widely used, particularly in North America, for the baking of soda crackers, but are also versatile and may be used for all types of biscuits, except high fat cookies (Figs. 13.19 13.22).

Biscuit Baking Technology

13.2 Compound balanced weave bands

FIGURE 13.19

Ashworth CB5 belt Ashworth CB5 belt.

FIGURE 13.20

Ashworth CB5 belt Ashworth CB5 belt.

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FIGURE 13.21 Rexnord Cambridge Engineered Solutions CB5 belts.

FIGURE 13.22 Rexnord Cambridge Engineered Solutions CB5 belts.

13.2.1 Compound balanced weave band supports Compound balanced weave bands are supported on rollers, which will carry heavy bands with low friction. The design of the supports and adjustment for levelling and the specification of the bearings are critical as the rollers operate at baking temperatures. If the rollers seize, they will quickly cause wear to the oven band. The ends of the rollers are therefore exposed for inspection, and high-temperature bearings must be used. The bearings are mounted outside the baking chamber and are insulated from the chamber (Fig. 13.23).

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FIGURE 13.23

Bearing assembly with SKF bearing type Y-V228 suitable for operating temperatures up to 350 C.

13.2.2 Band tracking for compound balanced weave bands The manufacture and joining of compound balanced weave bands is important for good tracking. These bands are made and delivered in 10 20 m lengths and will be joined on site. The joining of these bands requires skill and experience. Ashworth bands are tracked by vertical side rollers positioned before each drum. These rollers are not intended to force the band into position. They do limit side movement and act as sensing devices to indicate tracking problems. The band control units should be located at each end of the oven before the terminal drum. The distance between the control unit and the drum should be 3 3 bandwidth. At this distance, the force required to move the band to its central position on the drum is small (Figs. 13.24 and 13.25).

FIGURE 13.24

Recommendation for position of control units.

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FIGURE 13.25 Ashworth control unit.

• • • • • •

Base frame with three band support rollers Four vertical rollers on each side of the band Bandwidth up to 1525 mm Suitable for all spiral wire-mesh bands Guide rollers adjust vertically to move wear point Available with carbon steel ball bearings for temperatures up to 350 C or with carbide zero wear bearings for higher temperatures, no lubrication required.

13.2.3 Joining Ashworth bands The bands are joined by inserting the correct number of connecting wires, depending on the type of mesh. The crimped connectors are inserted and seated so that the weave is flat. The connecting wires extend each side by 2 mm and are fastened to the end spirals by a simple weld (Figs. 13.26 13.28).

FIGURE 13.26 Ashworth CB5 band: five connectors.

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13.3 Steel bands

FIGURE 13.27

Ashworth CB3 band: three connectors.

FIGURE 13.28

Ashworth Unilateral weave: one connector.

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Note: extensive technical data is available at http://www.ashworth.com.

13.2.4 Dimensions of compound balanced weave bands The dimensions of compound balanced weave belts are given in Table 13.2.

13.3 Steel bands TABLE 13.2

Compound balanced weave belts. CB 5

Belt thickness (mm) 2

Weight (kg/m )

1.6 2.0 14.0 20.5

These bands are made from thin (usually 1.2 mm) carbon steel and are suitable for soft doughs, which flow on the band when heated. They are used for all deposited cookies and cakes, such as layer cake which

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are baked directly on the oven band. Traditionally steel bands are also used for baking ‘Marie’ biscuits (Table 13.3 and Figs. 13.29 13.33). TABLE 13.3

Steel belts.

Belt thickness (mm) 2

Weight (kg/m )

1.0 1.4 8.0 14.1

Typical figures.

FIGURE 13.29

Cookies deposited directly onto a steel band.

FIGURE 13.30 Steel band on delivery end drum.

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FIGURE 13.31 Steel band with acive integrated tracking from IPCO. The unit is suitable for aplications with low belt speeds. https://ipco.com.

FIGURE 13.32 High Precision Tracking from IPCO. This unit is suitable for high belt speeds and high tracking accuracy.

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FIGURE 13.33 Bearing housings from IPCO.

13.3.1 Steel band supports Steel bands are successfully supported on skid bars as described above. Skid bars are manufactured and recommended by IPCO. These are recommended for high-temperature baking applications (Fig. 13.34).

FIGURE 13.34 IPCO cast iron and graphite skid bars.

In the case of steel bands, the skid bars are 75 100 mm narrower than the band. The pitch of the skid bars should be 0.8 1.0 m. Special soft graphite skid bars may be used at the feed end of the oven. Approximately four graphite skid bars are used for a 30-m long baking chamber. These graphite skid bars lubricate the inside of the band and reduce friction. The soft graphite skid bars apply graphite in an even, continuous, automatic way. They provide the following advantages: • The skid bars are ideal for heavily loaded bands. • The band does not need additional lubrication at start up or during operation. • Band life is increased. • Can be used in conjunction with cast iron skid bars to help to reduce friction and eliminate any slip-stick problems.

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Hard graphite skid bars are also available. These provide a long life at high temperatures. They may be used in place of cast iron skid bars (Fig. 13.35).

FIGURE 13.35

IPCO graphite station.

The IPCO graphite station is a standardised solution for depositing graphite on the underside of the steel belt. The support brackets are spring-loaded to keep the graphite bars in constant contact with the belt. A safety mechanism prevents the belt from contacting the support structure.

13.3.2 Joining steel bands Steel bands may be riveted, and IPCO supply riveting kits including the tools and instructions. However a much better method is welding, which provides a completely smooth surface to the join. Welding is a specialist operation carried out by the band supplier with specialist equipment for welding and tempering the joint. IPCO provide equipment and specialist engineers.

13.3.3 Steel band cleaners Steel bands may be cleaned by scrapers and may be assisted by rotating brushes (Fig. 13.36).

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FIGURE 13.36 IPCO steel band cleaner.

The IPCO belt cleaning device is an easily installed frame with an electronically controlled rotating brush. Brush speed is variable, and there are several brush materials available to suit different applications. For steel belts, steel scrapers may be used for cleaning. Up to three rows of spring steel scrapers in a staggered formation are mounted on the adjustable frame. The frame is raised by a lever to scrape the band. The pressure is adjustable (Fig. 13.37).

FIGURE 13.37 Steel band scrapers on a cake oven.

For very sticky products, hot water washer units may be used. These are located close to the delivery end of the oven, where the band is still hot. The washer may be used continually or intermittently as required. The water is sent to drain. After washing, the band should be dried and oiled to prevent rust.

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13.3.4 Steel band greasing At the feed end drum, the band may be greased to prevent the dough sticking. The grease is deposited from a hopper onto soft pads which are mounted on a reciprocating arm. This moves across the band, back and forward to smear an even coating of grease on the steel band.

13.3.5 Steel band tracking Spring-loaded guide rollers provide a robust and safe way to keep a band running within acceptable side movements. A pair of side guide rollers may be installed outside the baking chamber (Fig. 13.38).

FIGURE 13.38

Spring-loaded side guide rollers from IPCO.

An active band tracking system may use tilting rollers activated by a band edge detection device. The tilting rollers are automatically raised on one side, creating a tight (higher tension) and a slack (lower tension) side to the band. The band will track towards the side with the lower tension (Fig. 13.39).

FIGURE 13.39

Compact belt tracker from IPCO.

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Further reading Agrati La Bridoire Sarl, 2021. http://www.agrati.com http://www.ovenband-labridoire. com. Ashworth Bros., Inc., 2021. Balanced Weave Belts, Cleaning Baking bands, Control Systems, Baking Bands—Installing. http://www.ashworth.com. Baker Pacific Ltd., 2021. http://www.bakerpacific.net. Baker Perkins Ltd., 2021. http://www.bakerperkins.com. Berndorf, 2021. Bake Oven Belts. http://www.berndorfband-group.com. Cambridge Engineered Solutions, 2021. http://www.cambridge-es.com. Euchner GmbH & Co. KG. http://www.euchner.co.uk. IPCO, 2021. The Industrial Process Solutions Company. http://www.ipco.com. Jan-Ola Jonsson, 2021. The Properties of Steel Belts. http://www.sciencedirect.com. P. Otten, 2021. Tunnel oven belts. http://www.biscuitpeople.com. P. Otten, 2021. Belt Tracking in tunnel ovens. http://www.biscuitpeople.com. Produits Trefiles de la Bridoire, 2021. http://www.ovenband-labridoire.com. Rexnord, 2021. http://www.rexnord.com. Sandvik Process Systems. Product Information. See IPCO. SKF, 2021. Product information. http://www.skf.com. W.H. Smith, 2021. Cleaning and Care of Oven Bands. Biscuit Maker and Plant Baker. 1967. http://www.sciencedirect.com. Steinhaus GmbH, 2021. Rolled Baking Oven Belts. http://www.bakingovenbelts.com. http://www.steinhaus-gmbh.de. 2021.

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C H A P T E R

14 Oven conveyor design 14.1 Oven conveyor The products are carried through the oven by a conveyor which has a turning drum at each end of the oven (Fig. 14.1).

FIGURE 14.1

Diagram of oven band circuit.

14.2 Feed end The feed end unit has the following functions: • • • •

Oven band drum support and movement Oven band tension Tracking Installation of equipment over the oven band (e.g. a wire-cut machine) (Figs. 14.2 14.4)

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14. Oven conveyor design

FIGURE 14.2 Baker Pacific feed end on a hybrid oven.

FIGURE 14.3 Baker Pacific feed end on a steel band oven with depositor.

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14.2 Feed end

237

FIGURE 14.4 Feed end assembly drawing showing: (1) Rigid structure anchored in the floor. (2) Oven drum supported on bearings mounted on slides. (3) Oven drum movement for tensioning the band. (4) Pneumatic cylinders for tensioning. (5) Oven drum scraper. (6) Band position detector.

14.2.1 Oven terminal drums 1. 2. 3. 4. 5.

Shaft Machined drum 1100 mm diametre with a taper of 2 mm at each side Cross and Morse clamping element Proximity switch Synatel speed monitor.

The oven terminal drums support the band as it turns. The drums are manufactured to high quality and close tolerances to ensure good band tracking. The tapered edges help to hold the band in position on the drum (Fig. 14.5).

FIGURE 14.5

Oven terminal drum for 1250 mm wide wire-mesh band (total width

1350 mm).

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The drum is secured to the shaft by special clamping elements. These elements use frictional forces to transmit high torque. Precision tapered thrust cones create high pressure between the shaft and the drum hub to secure the drum. Large clamping surfaces ensure the pressure level is not excessive (Fig. 14.6).

FIGURE 14.6 Cross 1 Morse clamping element RCK11.

The drum shaft pillow block bearings are mounted on precision slides to allow the feed end drum to move to provide the band tension. The drum must move exactly at right angles to the direction of band travel, and therefore, the rigidity of the feed end structure and the slides are critical (Figs. 14.7 14.11).

FIGURE 14.7 Feed end assembly with pneumatic cylinder, drum bearing with Synatel speed monitor, drum scraper and band position detector. Biscuit Baking Technology

FIGURE 14.8

Star linear ball rail slides from Rexroth Bosch.

FIGURE 14.9

Star linear ball rail slides from Rexroth Bosch.

FIGURE 14.10

Martonair pneumatic cylinder for tensioning the band.

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14. Oven conveyor design

FIGURE 14.11 Synatel speed monitor for drum rotation.

The tension is applied to the bearing blocks by chains pulled by pneumatic cylinders mounted on each side of the feed end unit.

14.3 Delivery end The delivery end unit has the following functions: • • • • • •

Oven band drum support Oven band drive Tracking Stripping knife and conveyor Installation of band cleaner Oven end hood and extraction fan (Figs. 14.12 14.14).

Biscuit Baking Technology

FIGURE 14.12 Baker Pacific oven delivery end with oven end hood and fan, band cleaner, band tracker with band position monitor.

FIGURE 14.13

Delivery end drum on a Baker Pacific oven producing layer cake.

FIGURE 14.14

Delivery end arrangement drawing.

242 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

14. Oven conveyor design

Oven end drum Band position detector Oven drum scraper Stripping conveyor Biscuit reject actuator Stripping conveyor drive roll Stripping knife Main motor 7.5 kW Reduction gearbox Emergency DC motor.

14.3.1 Delivery end drum The drive shown is for a 1.25 m 3 100 m biscuit oven. The main motor is 7.5 kW with a reduction gearbox. The DC motor is powered by batteries and operates automatically in the event of a power failure to empty the oven of products (Figs. 14.15 14.17).

FIGURE 14.15 Baker Pacific delivery end drum, band position detector, drum scraper, main and DC motors. The drum design and construction is the same as the feed end drum.

Biscuit Baking Technology

14.3 Delivery end

FIGURE 14.16

Drum scraper.

FIGURE 14.17

Main drive and emergency DC motor with sprag clutch.

243

14.3.2 Oven drive The oven is driven from a 7.5 kW AC motor through a toothed belt drive to a reduction gearbox. The gearbox is mounted on a 60 mm diameter shaft which transfers the drive to the opposite side of the delivery end

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unit. The speed is further reduced by the chain and sprocket transmission. The chain drive is also used to drive the stripping conveyor. In this mode, the DC motor is idle due to the orientation of the sprag clutch. The motor is controlled by inverter to provide a speed range of 3.33 33.3 m/min, (corresponding to a 3 min baking time). If a power cut occurs, the DC motor is automatically engaged. The power is transmitted by a toothed belt drive to the reduction gearbox. In this mode, the AC motor is idle. The DC motor drives the oven band at 6.44 m/min to empty the oven of dough pieces (Fig. 14.18).

FIGURE 14.18 Chain and sprocket drives to the drum and the stripping conveyor.

14.3.3 Sprag clutch The sprag clutch is a one-way free-wheel clutch suitable for overrunning. It has an inner and an outer race with precision ground cams in contact with both races. The clutch drives both the main drive and the emergency drive (Fig. 14.19).

Biscuit Baking Technology

14.3 Delivery end

FIGURE 14.19

245

Cross 1 Morse MO500 clutch.

14.3.4 Uninterruptible power supply The oven requires an emergency drive system to operate automatically in the event of a power failure. This may be a factory generator which automatically takes over the power supply and supplies the oven drive. Alternatively a DC motor and battery power may be used (Fig. 14.20).

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FIGURE 14.20 AC motor at the top and DC motor below.

The battery pack is continuously charged during normal operation. In the event of a power failure, the batteries will power the DC motor at 2.55 kW for 15 min to empty the oven of biscuits. The band speed will be 6.44 m/min (Figs. 14.21 and 14.22).

Biscuit Baking Technology

14.3 Delivery end

FIGURE 14.21

Erskine charger and battery pack.

FIGURE 14.22

Erskine charger and battery pack.

247

14.3.5 Stripping conveyor The biscuits are stripped from the oven band by a knife and transferred to the stripping conveyor. This is usually a wire-mesh conveyor driven by the main oven drive (Figs. 14.23 14.25). 1. Stripping knife at oven end 2. Stripping conveyor 3. Drive roll

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FIGURE 14.23 Stripping conveyor arrangement: side elevation.

FIGURE 14.24 Stripping knife: transfer from oven band to stripping conveyor.

FIGURE 14.25 Transfer from stripping conveyor with retractable end for biscuit reject.

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4. Weighted tension roll 5. Biscuit reject mechanism. Burnt or broken biscuits may be rejected at the end of the stripping conveyor by the operation of an air cylinder which retracts the end nosepiece of the conveyor. The biscuits will fall onto a narrow cross conveyor which will automatically start and will deposit the scrap biscuits into a bin at the side of the line (Fig. 14.26).

FIGURE 14.26

Cross conveyor to collect scrap biscuits from the reject.

14.3.6 Oven end hood design Recommended design (Figs. 14.27 and 14.28):

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14. Oven conveyor design

FIGURE 14.27 Oven end hood.

FIGURE 14.28 Baker Pacific oven end hood.

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• Low hood • Fully enclosed at sides • Bifurcated fan close to the oven end.

14.3.7 Calculation of oven band tension The formula is T 5 (WLfr 1 wLfr) where T is band tension in kg/m of bandwidth; W is a total weight 5 band weight 1 product weight in kg/m2; L is a conveyor length in m; w is a band weight in kg/m2 and fr is a coefficient of friction between the band and supports. Typical fr values: Cast iron skids (dry) 0.23 0.4 Cast iron skids (lubricated) 0.13 0.21 Rollers (free turning) 0.10 Example: Z47 wire-mesh band: weight 7.3 kg/m2 Product: Marie type: weight of dough pieces 1.87 kg/m2 Conveyor length: 110 m Coefficient of friction (rollers) 0.1 W 5 Total weight 5 7.3 1 1.87 5 9.17 kg/m2 L 5 conveyor length 5 110 m w 5 band weight 5 7.3 kg/m2 fr 5 rollers 5 0.1 T 5 (9.17 3 110 3 0.1 1 7.3 3 110 3 0.1) kg/m of bandwidth T 5 (100.87 1 80.3) T 5 181.17 kg/m of bandwidth For bandwidth of 1.2 m: Tension 5 217.4 kg.

14.3.8 Calculation of torque required for the conveyor drive Torque 5 Tension 3 0.5 3 drum diameter For a drum 1.1 m diameter Torque 5 217.4 3 0.5 3 1.1 5 119.57 kg force Torque 5 1173 N m 1 kg force 5 9.807 N m

14.3.9 Calculation of electric motor power Power (kW) 5 torque (N m) 3 speed (rpm)/9.554 Example: The torque requirement is 1173 N m

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Oven baking time 3.0 min on 100 m long oven gives band speed of 33.33 m/min. Drum diametre 1.1 m with drum circumference of 3.46 m Drum speed 5 33.33/3.46 5 9.63 RPM Power (kW) 5 torque (N m) 3 speed (RPM)/9.5488 Power (kW) 5 1.18 (From WENtechnology calculation) (Fig. 14.29).

FIGURE 14.29 Delivery end and transfer to cooling conveyors.

Further reading Baker Pacific Ltd. Cambridge CB24 9YZ, United Kingdom. www.bakerpacific.net. Cross 1 Morse. Shady Ln., Birmingham B44 9EU, United Kingdom. www.cross-morse.co.uk. Erskine: Dale Power Solutions. Salter Road, Eastfield Industrial Estate, Scarborough, YO11 3DU, United Kingdom. www.dalepowersolutions.com. Festo. Esslingen, Germany. www.festo.com. Martonair. www.martonair.co.uk, www.aircat.co.uk, www.norgren.com. Bosch Rexroth. Lohr a. Main, Germany. www.boschrexroth.com. S. Eldridge Design Ltd. 37 Hazelwood Cl, Honiton EX14 2XA. www.seldridgedesign.co.uk. Synatel. Walsall Rd, Norton Canes, Cannock WS11 9TB, United Kingdom. www.synatel.co.uk. WENtechnology/Unipower. 8411 Garvey Dr STE 117, Raleigh, NC 27616, USA. www.wentec.com/unipower.

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C H A P T E R

15 Process control systems 15.1 Temperature control 15.1.1 Direct gas-fired ovens Direct gas-fired (DGF) ovens have the most complete system of temperature control. The system can provide separate top and bottom control of heat input from the burners and lateral control across the width of the oven with multi-lane distributor burners.

15.1.2 Indirect radiant ovens Indirect ovens have a single burner in each zone; therefore, the temperature is not variable from top to bottom or across the width of the oven. Baking control is by varying the airflow to the top and bottom radiant tubes. Lateral control is by means of adjustable restriction plates on the inlet to the radiant tubes (this is set at commissioning to provide an even bake across the width of the oven).

15.1.3 Convection ovens Similar to indirect radiant ovens, convection ovens have only one burner in each zone. The temperature of the airflow to the top and bottom of the oven and across the width of the oven is the same. The airflow to the top/bottom of the baking chamber is varied by damper controls. The air movement in the baking chamber may affect the heat transfer across the width of the oven.

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15.1.4 Electric ovens The temperature is controlled by varying the current to the top and bottom heater elements in each oven zone. A computerised computer system would give close temperature control down the length of the conveyer controlling each zone individually. The conveyer belt speed could also be controlled from the panel with safety devices for alarms, over temperature and belt stoppage.

15.1.5 Temperature monitoring and control The temperature is controlled separately in each oven zone. The temperature is detected within the baking chamber by ‘K’ type thermocouples. The thermocouples are connected to the temperature controllers by special screened cable: NiCr/Ni type K (Fig. 15.1).

FIGURE 15.1 ‘K’ type thermocouple with the insulated head from TC Direct.

Normally in a DGF or electric oven, there will be four thermocouples in each zone, two above the band and two below. The thermocouples are connected to temperature controllers on the zone control panel. The controller will average the temperatures from the two thermocouples at the top of the baking chamber and the two thermocouples at the bottom of the oven. There is a separate controller and separate system for controlling the top burners and the bottom burners.

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The position of the thermocouples is important, and the location should not be close to a burner flame or heater element, which will give a misleading temperature reading. In a DGF oven, the location should be adjacent to the back of the burner (opposite side to the flame) and as far from the burners as possible. Locations close to an inspection door or at a zone end are often chosen for DGF and electric ovens. For Indirect radiant or convection ovens, the control is for a single burner in each zone and the oven may have a single or multiple thermocouples from which the temperatures are averaged by the controller. Thermocouples would normally be located in the baking chamber on each side of the heater module.

15.1.6 Temperature controllers The thermocouples provide temperature data to automatic controllers. The required baking temperature is set at the controller by push button, and the controller will display the set temperature and the actual temperature. In addition a simple controller is used to detect an over-temperature condition which could be unsafe. A thermocouple in the zone flue or heat exchanger will detect an excessive temperature (as set on the controller) and will automatically shut down the burner system by operating the gas solenoid valve if the temperature exceeds the maximum set point (Figs. 15.2 and 15.3).

Biscuit Baking Technology

FIGURE 15.2 Zone control panel for two zones on a direct gas-fired oven with Omron temperature controllers. Each zone has a separate top and bottom controller and a safety override controller.

15.1 Temperature control

FIGURE 15.3

257

Temperature controllers.

15.1.7 PID control Temperature controllers use PID: proportional-integral-derivative. PID is a control loop feedback system. The controller monitors the actual temperature compared to the set point and activates the burner control to maintain the set point temperature. By tuning the three parameters of the PID controller algorithm, the system will respond accurately and promptly to variations between the set point and the actual baking temperatures. When the PID is tuned with the correct values for P, I, and D, the system will be responsive and will maintain the baking temperature within 6 1 C avoiding overshooting and undershooting. Proportional term produces an output value proportional to the current error value (the difference between set and actual temperatures). The controller response can be adjusted by the proportional gain constant. A high proportional gain results in a large change in output for a given change in error. Integral term is proportional to the magnitude and the duration of the error. Derivative term slows the rate of change of the controller output. Derivative term adjustment can be used to reduce overshoot and improve process-controller stability (Fig. 15.4).

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FIGURE 15.4 Neles Expertune PID loop optimizer.

15.1.8 Top and bottom temperature control The top burners and the bottom burners in each zone have independent temperature controllers and air supply via separate motorised valves (Figs. 15.5 and 15.6).

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15.1 Temperature control

FIGURE 15.5

Temperature control panel.

FIGURE 15.6

Separate top and bottom burner control.

259

It should be noted that a change in setting to either the top or bottom burners will affect both top and bottom systems. The oven has one baking chamber, but two separate temperature control systems which interact. For example, if a change is made to the bottom temperature setting, the bottom burners will increase or decrease the heat input. If the bottom heat is increased, more hot air will rise in the baking chamber and the top temperature sensors will detect over temperature. The controller will then automatically reduce the heat input from the top burners (Fig. 15.7).

FIGURE 15.7

Increase in bottom temperature.

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If the bottom heat is decreased, less hot air will rise and the top temperature sensors will detect under temperature. The controller will increase the top burners to compensate (Fig. 15.8).

FIGURE 15.8 Decrease in bottom temperature.

15.2 Baking time The baking time is simply altered by adjusting the conveyor speed. The motor is an AC motor with inverter control. The speed range will depend on the range of products to be made: for example, a cracker oven may have a baking time range of 2.5 7.5 min, a cookie oven from 4.0 to 12.0 min (Fig. 15.9).

FIGURE 15.9 The PAX Lite Process Time indicator from Red Lion Controls.

15.3 Humidity Control of the humidity in the baking chamber is by extraction of the moisture through a fan and flue. Each zone has a series of extraction duct inlets (cross ducts) at the top of the baking chamber which connects to an extraction duct along the length of the zone. The extraction duct conveys the wet air to the extraction fan, which exhausts it through the flue. During the first part of the baking process, the baking chamber has high humidity to enable the biscuit structure to form without the outer skin of the dough pieces drying. After the structure of the biscuits is formed, the baking process requires moisture to be evaporated from the

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dough pieces. The extraction system exhausts the moisture from the baking chamber to reduce the moisture content of the biscuits to the required level. If a DGF oven is burning LPG fuel, extraction ducts should be installed at the top and bottom of the baking chamber. LPG is heavier than air, and unburnt gas can lie at the bottom of the baking chamber and cause an explosion if ignited (Figs. 15.10 15.14).

FIGURE 15.10 Plan of the top of the baking chamber showing position of the extraction duct.

FIGURE 15.11

Extraction duct at the top of the baking chamber.

FIGURE 15.12

Extraction duct.

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FIGURE 15.13

15. Process control systems

Halifax 12P multi-vane extraction fan on a DGF oven. DGF, Direct gas-

fired.

FIGURE 15.14 Halifax 12P multi-vane extraction fan on a DGF oven. DGF, Direct gas-fired.

The amount of air extracted from the baking chamber is controlled by a damper in the fan inlet duct. This may be controlled manually or by servo motor. An alternative control system is a variable-speed extraction fan.

15.4 Colour control The colour is controlled in the final zones of the oven. The biscuit colour develops rapidly when the surface of the dough pieces is dry and at a temperature over 150 C.

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A typical problem may be poor lateral control (across the width of the band). This may apply to both colour and moisture content. The first check for problems of lateral control should be at the forming machines. If the dough piece weights vary across the width of the band, the colour and moisture content after baking will also vary. Ovens may have systems of lateral baking control. These may be summarised as: • DGF ovens: Multi-lane burners • Indirect radiant ovens: Control of airflow to the radiant tubes • Convection ovens: Control of return airflow to the circulation fan

15.4.1 Direct gas-fired ovens Multi-lane burners allow the burner flame to be adjusted in several lanes across the width of the oven. The burners may have three or five lanes. By adjusting the flame in the centre and/or at each side, the heat input can be balanced and an even colour achieved. In order for the system to be effective, at least 15% of the burners should be multi-lane (Figs. 15.15 and 15.16).

FIGURE 15.15

Flynn 3 lane distributor burner.

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FIGURE 15.16 Flynn 3 lane distributor burner.

15.4.2 Indirect radiant ovens Indirect radiant ovens bake by radiation from tubes carrying the hot air/gases from the burner. The hot gases enter the radiant tubes from distribution ducts across the width of the oven. In these ducts, there are sliding plates which carry adjustable restrictors which will reduce the hot gases entering each radiant tube. These restrictor plates are adjusted during commissioning and ensure well-balanced lateral heating (Figs. 15.17 and 15.18).

Biscuit Baking Technology

FIGURE 15.17 Indirect radiant oven: distributor ducts with restrictor plates for controlling the airflow to the radiant tubes.

FIGURE 15.18 Indirect radiant oven: distributor ducts with restrictor plates for controlling the airflow to the radiant tubes.

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15.4.3 Colour measurement Usually examples of the correct biscuit colour will be held on a frame at the end of the oven for comparison with the baked biscuits being made. The oven operator may visually check the bake against samples of the correct colour range. For the laboratory, a spectrophotometer will be used (Fig. 15.19).

FIGURE 15.19 Konica Minolta CM-5 Spectrophotometer.

The spectrophotometer allows the technician to set up measurements of reflectance and transmittance and a judgement of pass/fail based on a set of tolerances. Data can be shown numerically or on spectral graphs.

15.5 PLC control PLC control, graphics with touch screen HMI or keyboard can provide all the baking control functions and displays. These may include all monitoring and control functions as described above and diagnostics,

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fault finding and alarm/warning alerts. The equipment control for dampers, valves, etc. will be motorised using servo motors and motor speeds controlled by inverters. The control system can be recipe driven, providing the correct settings according to the recipe selected. The control/monitoring is presented to the oven operator by an HMI, for example, Allen Bradley Panel View (Fig. 15.20).

FIGURE 15.20

PLC screen for ingredient handling system.

The Allen Bradley operator terminals are ideal for baking oven applications that require monitoring, controlling and displaying information in dynamic ways, where operators must quickly understand machine status and make correct decisions (Figs. 15.21 15.23).

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FIGURE 15.21 PLC screen for oven data and control.

FIGURE 15.22 Kollmorgen servo motor for control of dampers.

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15.5 PLC control

FIGURE 15.23

Inverter speed control from Danfoss.

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In addition to the control, display, alarm functions, the system may provide historical data trending to enable the technicians to better manage recurring faults, downtime, product variations in colour, moisture content and other operational factors (Figs. 15.24 and 25).

FIGURE 15.24

Vaisala sensor DMP6 for high temperature and humidity oven applications.

FIGURE 15.25 Vaisala Indigo 500 transmitter.

The oven PLC/HMI system can be linked to a SCADA (supervisory control and data acquisition) system which may include multiple production lines and factory sites. The SCADA system’s database and software can provide trending, diagnostic data and management

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information such as maintenance schedules and reports, expert system trouble-shooting and comparison data of oven performance.

15.5.1 Specification for a PLC control system • • • • • • • • • • • •

Control of all heaters/burners Over-temperature protection Control of fan motors and conveyor drive motor inverter Door interlocks Emergency mushroom button Full safety chain for over temperature, belt stop, extraction fans, inverter fault. Network analyzer to be interfaced with PLC and monitor. I/O modules ANALOGIC and LOGIC for all the diagnostic Transmission modules and Interface modules for PC touch 19v Graphic layout of the oven with all the sensors measurement (temperature, fans, conveyor belt speed, warnings, alarms). All necessary SSR’s, contactors and fuses. The system can be connected via router and VPN connection

Further reading Allen Bradley. Rockwell Automation Inc. Milwaukee, Wisconsin, USA, http://www.rockwellautomation.com. Antunes pressure switches, 180 Kehoe Blvd, Carol Stream, IL 60188, USA, http://www. ajantunes.com. Avevat Group plc, High Cross, Madingley Road, Cambridge, CB3 0HB, United Kingdom, http://www.aveva.com. Baker Pacific. Cambridge CB24 9YZ, United Kingdom, http://www.bakerpacific.net. Danfoss A/S. Nordborgvej 81, 6430 Nordborg, Denmark, http://www.danfoss.com. DhEsrl, Thermowatt S.p.A, Via S. Giovanni, Battista 21, 60011 Arcevia AN, Italy, http:// www.dhesrl.com. Flynn Burner Corp. 225 Mooresville Blvd, Mooresville, NC 28115, USA, http://www. flynnburner.com. GTB Controls. 90 Ernest Rd, Wivenhoe, Colchester CO7 9LJ, United Kingdom, https:// gttb.com. Kollmorgen s.r.o. Evropska´ 864, 664 42 Modˇrice, Brno, Czech Republic, http://www.kollmorgen.com. Konica Minolta Inc. JP Tower, 2-7-2 Marunouchi. Chiyoda-ku, Tokyo 100-7015, Japan, http://www.konicaminolta.com. Metso Expertune. Automation.com, PO Box 12277, Research Triangle Park, NC 27709, USA, [email protected], http://www.expertune.com. Micromech Ltd. 5-8 Chiford Court, Rayne Road, Braintree, Essex, CM7 2QS, United Kingdom, http://www.micromech.co.uk. Neles Corporation. Owner: Valmet Corp. PO Box 304, FI-01301, Vantaa, Finland, http:// www.neles.com. Omron. Kyoto, Japan, http://www.omron.com.

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Red Lion Controls. 20 Willow Springs Circle, York, PA 17406, USA, http://www.redlion. net. Schneider-Electric: 35 Rue Joseph Monier CS30323, F-92506 Rueil-Malmaison, France, http://www.se.com. Selas Heat Technology Company, 11012 Aurora Hudson Road, Streetsboro, OH 44241 USA, http://www.selas.com. Synatel Instrumentation Ltd. Walsall Road, Norton Canes, Cannock, Staffordshire, WS11 9TB, Unied Kingdom, http://www.synatel.co.uk. Thermowatt S.p.A, Via S. Giovanni, Battista 21, 60011 Arcevia AN, Italy, http://www.thermowatt.com. Vaisala Oyj, Vanha Nurmijarventie 21, 01670 Vantaa, Finland, http://www.vaisala.com. Weishaupt Corp. Max Weishaupt GmbH, Max- Weishaupt Strasse, 1488477 Schwendi, Germany, http://www.weishaupt-corp.com.

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C H A P T E R

16 Oven safety monitoring and alarm 16.1 Oven band safety systems 16.1.1 Oven band tracking It is essential that the oven band runs in the centre of the baking chamber, with minimum movement from side to side. If the band deviates excessively, the band edges can contact side guide rollers or cast iron side guides. More deviation will result in the band contacting oven parts which will damage the edge of the band. If the band wanders to one side, there are several possible causes: 1. Uneven band loading (dough pieces missing or not consistently panned evenly across the width of the oven). 2. Uneven heat application by direct gas-fired (DGF) burners or the convection or radiant systems. 3. Poor oven band joints with a tight side and a slack side in the band circuit. 4. Oven band support rollers or skids are not level or not at right angles to the direction of band travel. 5. Oven terminal drums are not correctly aligned. 6. Lack of oven band tension or uneven tension. 7. Oven tension end drum is not moving freely and evenly on the slides. 8. Poor quality wire-mesh band with uneven mesh.

16.1.2 Detection of the oven band position The oven band will be monitored for excess movement using limit switches at each end of the oven (Fig. 16.1).

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FIGURE 16.1 Oven band tracking system in front of the terminal drum at the delivery end of the oven. Note the side guide rollers to detect the band movement and air cylinders controlling the tracking roll.

If the oven band moves 10 mm to one side, the vertical roller will be pushed and this will actuate the Euchner limit switch. An alarm will sound, and the tracking roller will be automatically moved to correct the tracking and bring the oven band back to a central position. If the band continues to move, at 25 mm deviation, the trip position, the system will automatically sound the alarm and stop the oven band drive. In this case, the engineer must rapidly assess the problem and take corrective action. Once the band can be re-started at a slow speed, an override control may be used to start the drive and run until the tracking system brings the band back to a central position. Note: the settings for the multi-position limit switch are recommended for the band deviation of 10 mm (alarm warning) and 25 mm (band stops). These settings may be adjusted by the engineer and should be frequently checked.

16.1.3 Oven band drive The oven band is driven by an AC motor with inverter control. To start the oven band drive, the band must be in a central position on each terminal drum and the air supply to the cylinders for tensioning the band must be operating. The band tension is monitored, and tension must be present before starting the oven band. The speed of rotation of the oven band drive is monitored by a Synatel unit mounted on the end of the drum shaft (Fig. 16.2).

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FIGURE 16.2

275

Synatel ‘Wirligig’ speed monitor.

The oven band drive will stop under certain conditions: 1. 2. 3. 4.

Power failure Excessive band-tracking movement Failure of band tension system Operation of an emergency stop button

In the event of a power failure causing the oven band to stop, a system must be immediately employed to run the band and empty the oven of biscuits. If the biscuits are not rapidly conveyed out of the oven, they will overheat and catch fire. The fire may damage the oven band and oven structure. When the band stops, the solenoid valve for the main gas supply will be automatically closed and all burners will be extinguished and the fans will stop. The fault must be rapidly found by an engineer. The band can be re-started by using an override pushbutton, and the band run slowly to empty the oven of biscuits, until the fault is corrected, and the oven can be run normally under automatic control.

16.1.4 Emergency stops Emergency stop buttons, clearly identified, should be positioned at each end of the oven and on the main control panels. If an emergency Biscuit Baking Technology

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stop button is actuated, the oven drive, gas supply and burners will shut down (Fig. 16.3).

oven band tracking on

off

biscuit reject

tracking warning

tracking fault

tracking over-ride

stop

FIGURE 16.3 Control panel at the oven delivery end with tracking warning lights, emergency stop and over-ride button to re-start the oven band.

16.1.5 Emergency oven band drive An automatic system is usually employed to drive the oven band in the event of a power failure. This may be an emergency generator in the factory to provide power immediately to the oven drive or a batteryoperated DC motor. For small ovens, for example, 20 30 m long, a manual oven band wind-out system may be employed. If a DC motor is used with battery power, during the emergency wind out (approximately 12 min), all safety systems will operate, but the fans are not powered. With a generator, three-phase UPS, all systems will operate, including the fans (Fig. 16.4).

FIGURE 16.4 Oven drive: main AC motor at the top right and emergency DC motor at the bottom right.

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16.1.6 Oven band tension system The tension is applied to the oven band by pneumatic air cylinders mounted at each side of the feed end unit. The air cylinders apply the tension through chains attached to the oven band terminal drum supports. The oven terminal drum bearings are mounted on slides which allow the drum to move freely and maintain its alignment at right angles to the direction of travel of the band. A compressed air supply provides air to the two pneumatic cylinders. The regulator that operates the cylinders is set at 2.7 3.4 bar (40 50 psi) on the regulator dial. At commissioning, the band tension is set by measuring the amount of sag of the band between two supporting rollers. This amount varies with each band type and may be specified by the band supplier. The air pressure is adjusted to achieve the specified sag in the band (Fig. 16.5).

FIGURE 16.5 Pneumatic cylinder with air supply to maintain band tension. The terminal drum bearings are mounted on linear slide bearings.

The air supply to the cylinders is applied via a reservoir so that the pressure is maintained in the event of a failure of the air supply. The system is monitored by a pressure switch in the air supply, and a fault will cause an alarm and warning light on the main panel to show.

16.2 Oven burners and gas system The safe operation of the oven heating system is ensured by the following equipment:

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16.2.1 Gas trains The gas train should include the following equipment to ensure the safe operation of the gas feed to the burners (Fig. 16.6):

FIGURE 16.6 Gas train.

• • • • • • •

Manual shut-off valve Two automatic solenoid shut-off valves for the safety system Gas filter Zero-pressure gas governor Gas pressure high/low detection Gas pressure gauges (2) at gas inlet and outlet of gas train Gas valve tightness proving facility (to check for leakage of gas)

16.2.2 Gas system The gas supply to the oven can be isolated by the manual gas valve. A high/low gas pressure switch is fitted to stop the oven being operated with unsafe gas pressures. An electrical solenoid valve is fitted; this allows the gas supply to the oven to be automatically switched on at the end of the oven purge periods and automatically switched off in the event of unsafe conditions. The gas leakage system checks that both of the main safety shut-off valves are operating correctly and able to completely stop the gas supply.

16.2.3 Main gas solenoid valves These valves are situated in the gas train to the oven. Their function is to open on completion of the oven purge and shut off immediately after a fault is detected.

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16.2.4 High-/low-pressure switch The gas high-/low-pressure switch is situated in the main gas supply to the oven. Its function is to shut off the burners if the gas pressure supply falls below 12 mbar or exceeds 20 mbar.

16.2.5 Zero gas governor The zero gas governor is normally situated in the gas train. Its function is to provide an even, low (3 mbar) gas pressure to the burners in each zone. An alternative system employs solenoid valves at each direct-fired burner, which also function as zero gas governors.

16.2.6 Purge system The extraction fans will operate with the dampers open to purge the baking chamber before lighting the burners. The purge cycle is 6 min in duration, and this is controlled by a pre-set timer. During the purge cycle, the volume of air in the baking chamber is exhausted and replaced by fresh air five times. The duration of the purge cycle and the volume of air expelled from the baking chamber are designed to comply with FM Global insurance standards. The start of the purge cycle and completion are shown by indicator lamps on the main control panel or the HMI screen. Following the completion of the purge cycle, the burners can be safely ignited.

16.2.7 Over-temperature safety In addition to the baking temperature controllers, a simple controller is used to detect an over-temperature condition which could be unsafe. A thermocouple in the zone flue will detect an excessive temperature (as set on the controller), and the safety system will automatically shut down the burners by closing the gas solenoid valves. An alarm will sound.

16.3 Direct gas-fired ovens: manual control of top and bottom burners In special circumstances, the engineer may operate the burners by manual control. Manual control may be selected on the temperature controller, and the ‘Up’ and ‘Down’ pushbuttons are used to achieve the required air pressure to the burners.

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16.3.1 Air system The combustion air is provided by separate fans for the top and bottom burners on a DGF oven. The fans have pressure switches to monitor operation.

16.3.2 Burner flame supervision The Flynn Ignition Control Unit provides for automatic ignition and safe supervision of the gas burner (Fig. 16.7).

FIGURE 16.7 Flynn Ignition Control Unit.

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The DGF burners have a single electrode for ignition and flame detection. These functions are controlled at each burner by an Ignition Control Unit. Ignition is achieved from a spark directed across the burner strip at the electrode from a high-tension transformer in the flame ignition unit. The start-up sequence is initiated by a switch on the unit or by a switch on the zone control panel. The control starts its sequence by checking that the flame probe (electrode) is signalling no flame. The high-voltage spark generator is then energised together with the solenoid valve. The spark and valve will remain energised until the gas is lit or the ignition safety period is completed. When the gas is lit, the flame is detected by the electrode causing the spark igniter to be de-energised. The solenoid valve will remain open until the electrical supply to the unit is terminated or the flame goes out. If the burner fails to ignite or the flame subsequently fails, the gas valve will be closed and the control unit will go to lockout. Re-set of the lockout followed by a new start-up sequence can only be achieved by interrupting the electrical supply to the unit for a minimum of 3 s. To light the burners, the following conditions must be met: 1. The switch on the flame supervision unit is ‘On’. 2. The ‘Ignition’ selector switch is turned to ‘On’. The burners will now light up in banks. As an additional safety precaution, there is a 10 s delay between each bank of burners lighting. The Flynn control unit for each burner allows the burner to be switched on or off. The burner flames are ignited and monitored by an electrode. A lamp indicates that the burner is on and a flame is present. If the flame fails, a warning red light will show and the gas supply to the burner will be shut off by the solenoid valve (Fig. 16.8).

FIGURE 16.8

Flynn gas burner.

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16.3.3 Gas/air mixture Each gas/air mixer has a screw adjustment to alter the ratio of gas to air supplied to the burner. The ratio is set by the engineer during commissioning to achieve an efficient combustion and a steady blue flame. To weaken the mixture (i.e. less gas), turn the regulating screw clockwise. Turn the screw counter-clockwise to make the mixture richer. Start with a rich mixture, which is indicated by a green or red coloured flame, and slowly weaken until the base of the flame is blue. The flame should sit on the strip with a bright blue cone. Burner heat output is controlled by the variation of air pressure, and since the gas is maintained at zero pressure, the gas/air ratio will remain constant and ensure a completely combustible mixture at all air pressures.

16.4 Indirect-fired ovens: Weishaupt burners Weishaupt burners have a combustion manager and gas pressure monitoring and shut-off valves. The burner ignition/shut-down sequences are controlled by a dedicated control unit. Flame failure, gas pressure, air pressure and fan pressure are monitored by the controller (Fig. 16.9).

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FIGURE 16.9

283

Weishaupt burner.

16.4.1 Excess temperature The zone temperature is monitored by a separate temperature controller. If the automatic temperature control system fails and the temperature in the baking chamber continues to increase over a safe level, the oven will automatically shut down. An excess temperature is pre-set on the controller, and if the temperature exceeds the pre-set, the gas supply will be shut off and all burners extinguished.

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16.5 Extraction, combustion air and circulation fans The operation of all fans is monitored by pressure switches. In the case of a fault, the system will give an alarm (sound and warning light on the control panel) (Fig. 16.10).

FIGURE 16.10 Antunes pressure switch for detection of fan operation.

16.5.1 Damper controls For burner ignition and the purge cycle, the extraction dampers must be fully open to ensure complete evacuation of any gas in the baking chamber. The damper open position is detected by a limit switch.

16.6 General safety equipment and instructions 16.6.1 Guards and safety devices Suitable guards and safety devices are incorporated in the oven design following the best industry standards. All safety guards and systems must be fully operational.

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The supervisory engineer installing the equipment must ensure that all guards are secured in position and that the safety devices and systems are set to operate correctly before the equipment is put into use.

16.6.2 Operation safety precautions Before starting the equipment, especially after a shutdown during which cleaning or maintenance activities have taken place, the equipment should be inspected to ensure that it has been correctly assembled and all guards and safety systems are in place. The equipment should always be run within the specified limits for speeds, pressures, temperatures, etc. The equipment should always be attended while in operation. Observe indicator lights and warnings that are displayed on the oven panels. Take appropriate action for any alarms and warnings. The oven requires periodic preventive maintenance to keep it operating safely and efficiently. Any operational problems should be investigated immediately, and the necessary action should be taken.

16.6.3 Cleaning and maintenance safety precautions The user is responsible for ensuring that safeties are in place for the isolation of the equipment, before any cleaning or maintenance tasks are commenced. All power, air and fuel sources should be locked out. Always ensure that the oven has cooled sufficiently before attempting any cleaning or maintenance. After any maintenance, carefully check that all screws, bolts, nuts and other fixings are securely replaced. Some cleaning and maintenance operations involve the use of compressed air.

16.6.4 Commissioning safety precautions Before starting equipment, the moving parts must be checked for freedom of movement by rotating by hand where possible. Where necessary, the direction of rotation of drives must be confirmed before they are put into operation. Correct lubrication of the equipment must be checked before it is operated. Before start up, the electrical equipment must be tested to detect any problems which may have occurred due to dampness or damage caused during transport or storage.

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16.6.5 Running the equipment without safety systems In normal circumstances, the equipment should not be operated unless all safety systems are fully operational. However on very rare occasions for specific tasks, it may be necessary to run the equipment with some guards or safety devices removed. Some electrical maintenance activities may require that the power is turned on. Note: The user is responsible for implementing safe working practice and procedures for this type of situation. The person who is to do the work must be an employee that the user has authorised and who has received training to be able to carry out the task safely and effectively.

16.6.6 Protection of employees Protective equipment should be used as required by the task: • • • • • • •

Hardhats Safety glasses Ear protection Gloves Overalls Dust masks Fume and dust extraction

16.6.7 Emergency shutdown To stop the equipment in an emergency, press one of the red Emergency Stop pushbuttons located at each end of the oven and on the main control panels. When an E-Stop is pressed, the oven band will stop, the fans will stop and the burner system will shut down. The safety problem should be immediately addressed and solved before re-starting the oven.

Further reading Antunes pressure switches, 2021. http://www.ajantunes.com Allen Bradley, 2021. http://www.rockwellautomation.com Baker Perkins Ltd, 2021. Oven operation and maintenance manuals. http://www.bakerperkins.com DhE srl, 2021. http://www.dhesrl.com Flynn Burner Corp, 2021. http://www.flynnburner.com Omron, 2021. http://www.ia.omron.com

Biscuit Baking Technology

Further reading

Neles Corporation, 2021. http://www.neles.com Red Lion Controls, 2021. http://www.redlion.net Schneider-Electric, 2021. http://www.se.com Selas ERB burners, 2021. http://www.selas.com Synatel, 2021. http://www.synatel.co.uk Thermowatt spa, 2021. http://www.thermowatt.com Weishaupt, 2021. http://www.weishaupt-corp.com

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C H A P T E R

17 Manufacture of biscuit ovens 17.1 Why build the oven locally? The cost of a quality imported baking oven will be approximately 40% of the total cost of a cracker line and up to 50% of the cost of a short dough biscuit line. Many international manufacturers of highquality large ovens are located in high-cost environments in Europe, the United States, Japan and Korea. Local manufacture near the bakery offers important cost savings (Fig. 17.1).

FIGURE 17.1

Baker Pacific direct gas-fired/indirect radiant oven built in China.

A considerable proportion of the oven cost is in building the steel structures, baking chambers, heat exchangers, frames, covers and insulation. This work can be carried out successfully in many countries. There is no need to import large steel fabricated items, with high capital cost, shipping cost and import duties, which can be manufactured successfully locally.

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The reduction in shipping a large number of containers reduces cost and also the carbon footprint of the project, which is now an important advantage (Figs. 17.2 and 17.3).

FIGURE 17.2

Direct gas-fired baking chambers manufactured in China.

FIGURE 17.3 Direct gas-fired baking chambers manufactured in China.

Most biscuit oven manufacturers now assemble their ovens into complete modules before shipment. This reduces the time required on-site to assemble the oven. However, it results in most of the assembly work being carried

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out in a high-cost environment and in incurring high shipping costs and import duties. Shipment of a typical oven may require 10 20 containers with both cost and time disadvantages to the project. The capability to manufacture ovens locally in the growing markets is an important advantage. • • • • • •

Reduced fabrication cost Reduced import duties Low shipping cost Oven assembly in a lower cost environment Part payment in local currency Establishment of a local service capability

17.2 Building baking ovens locally: the tasks and team 17.2.1 The team and experience required Project manager (Fig. 17.4)

FIGURE 17.4

The team. Biscuit Baking Technology

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• Mechanical engineering • Biscuit production equipment • Purchasing Design engineer • • • •

Mechanical engineering design Software: CADCAM, Solid Works or equivalent Steel fabrication experience Pneumatic systems, conveyor drives and transmissions Electrical engineer

• • • • •

Control and safety systems and components Temperature control systems Pneumatic systems for conveyors PLC and PID system software Commissioning experience Local manager

• Language, technical, commercial and financial experience Installation engineer • Fabrication/installation experience (Fig. 17.5)

FIGURE 17.5

Baker Pacific engineer, local manager and contractor.

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17.3 Manufacturing drawings

293

17.3 Manufacturing drawings Layout drawings are produced in Solid Works and Corel Draw to set out the design concept. A layout drawing is then made to meet the customer’s requirements. Following the agreement, a drawing is made showing foundations and installation details (Figs. 17.6 and 17.7).

FIGURE 17.6

Design layout drawing for a direct gas-fired oven section.

FIGURE 17.7

Oven foundation drawing. Biscuit Baking Technology

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17. Manufacture of biscuit ovens

The assemblies and parts are drawn in Solid Works with 3D pictures. The software provides checks for all the dimensions and the assembly of parts (Figs. 17.8 17.12).

FIGURE 17.8 SolidWorks model for DGF oven. DGF, direct gas-fired.

FIGURE 17.9 Selected component from the assembly drawing: Inspection Door.

Biscuit Baking Technology

17.3 Manufacturing drawings

FIGURE 17.10

Selected component from the assembly drawing: Inspection Door.

FIGURE 17.11

Component assembly and exploded view of assembly.

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296

17. Manufacture of biscuit ovens

FIGURE 17.12 Component assembly and exploded view of assembly.

17.4 Control and safety systems For hard-wired control panels, wiring diagrams with parts lists are produced by the electrical engineer. The local contractor will make AutoCAD drawings for approval and inclusion in the Operation Manual. For PLC-controlled ovens, the software is provided by a specialist contractor (Fig. 17.13).

FIGURE 17.13 Electrical control panels from Baker Pacific contactor Qiyuan, China. Biscuit Baking Technology

17.5 Contractors

297

17.5 Contractors Baker Pacific has manufactured ovens in China, India and Indonesia. The projects rely on having a first-class local manager, conversant in technical, commercial, financial matters as well as language. To select a suitable local contractor, consideration is given to (Figs. 17.14 and 17.15):

FIGURE 17.14

Fabrication work in China.

FIGURE 17.15

Indirect radiant heater module made in India.

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17. Manufacture of biscuit ovens

Location/communication Capabilities: steel fabrication and assembly/factory space Quality standard for food industry Drawing standards and language Purchasing of materials and components

17.6 Purchasing Purchase orders are placed on contractors and suppliers detailing specification, price, terms of payment, delivery and commercial terms, for example, guarantees. Currency may be in USD, Euro, GBP and local currency. • • • • • • • • • • •

Bearings Burners Clamping elements, chains, sprockets, pressure switches, etc. Electrical equipment and panels, PLC thermocouples, UPS Motors and gearboxes Fans and blowers Gas equipment Insulation and seals Oven bands Pneumatic equipment Powder coatings

17.7 Shipping It is important to select a shipper who will handle a wide range of components from multiple sources. Baker Pacific shipping has been managed by PT Geodis Wilson and DFS Worldwide. They arrange to pick up from contractors anywhere in the world and arrange shipment and delivery CIF to the customer (Fig. 17.16).

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17.8 Installation

FIGURE 17.16

299

Shipping by the container.

17.8 Installation The oven is delivered as “kits of parts” corresponding to the sequence required for the installation. Baker Pacific provides two supervisory engineers for installation and commissioning. They supervise the work carried out by local staff provided by the customer (Figs. 17.17 and 17.18).

FIGURE 17.17

Installation team.

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17. Manufacture of biscuit ovens

FIGURE 17.18 Installation of a Baker Pacific indirect radiant oven with heat recovery system.

17.9 Summary • The baking oven represents the major part of the investment for a biscuit, cookie and cracker production line. • The major suppliers internationally manufacture in high-cost environments in Europe, the United States and Asia. There are major cost benefits in establishing a capability for local manufactures. • A small team of engineers, typically five, is required. Most medium to large biscuit manufacturers and bakery oven suppliers will have the suitable capability.

Further reading Baker Pacific Ltd, 2021. Cambridge CB24 9YZ, United Kingdom. http://www.bakerpacific.net. DFS Worldwide, 2021. Unit 7 Marlin Park, Central Way, Feltham, TW14 0AN, United Kingdom. http://www.dfsworldwide.com. Era-tec, 2021. 80 rue Rene´ Descartes38090 Vaulx-Milieu, France. http://www.era-tec.com. Esspee Engineers, 2021. Kolkata, India. http://www.espenger.com. Flynn Burner, 2021. 225 Mooresville Blvd. Mooresville, NC 28115, USA. http://www. flynnburner.com. Geodis Wilson, 2021. Activehouse, Watkins Close, Burnt Mills Industrial Estate, Basildon, Essex SS13 1TL, United Kingdom. https://.geodis.com. Halifax Fans, 2021. Unit 11, Brookfoot Business Park, Elland Rd, Brighouse HD6 2SD. http://www.halifax-fan.co.uk.

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Further reading

301

Moro, 2021. Via Pirandello 10, Barlassina, MB, Italy. http://www.ventilatori-industriali.eu. S. Eldridge Design Ltd, 2021. 37 Hazelwood Cl, Honiton EX14 2XA, United Kingdom. http://www.seldridgedesign.co.uk. Suzhou Dongshan Precision Manufacturing Co, 2021. http://www.sz-dsbj.com. Weishaupt, 2021. Max Weishaupt GmbH Max-Weishaupt-Straße 1488477 Schwendi. http://www.weishaupt-corp.com.

Biscuit Baking Technology

C H A P T E R

18 Oven operation: direct gas-fired oven 18.1 Starting the direct gas-fired oven: preparation 18.1.1 Baking programme Allow 30 min from start up before baking for the required baking temperatures to be reached high baking temperatures may take longer.

18.1.2 Burner pattern Normally all burners will be alight, and the automatic temperature control system will adjust the heat input to maintain the set baking temperatures by modulating the burner flames. If a very low heat input is required for a product, some burners may not be required and the oven may be operated without these burners. Burners can be closed by an on/off switch on the Ignition Control Unit at each burner. The burners switched off should be evenly distributed throughout the zone.

18.1.3 Before starting the oven 1. 2. 3. 4.

Check that the stripping knife at the oven end is disengaged. Check that the oven feed and delivery ends are clear of obstructions. Ensure that all inspection and access doors are closed. Before starting the oven, ensure that the air supply is turned on for the band tension and band-tracking systems. 5. Open the main supply manual gas valve. 6. Switch on the main control panel isolator (Fig. 18.1).

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FIGURE 18.1 Main control panel and zone control panels at the oven end.

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18.1 Starting the direct gas-fired oven: preparation

7. Switch on the zone panel isolators. At each zone panel (Fig. 18.2):

baker pacific

3

burner fan

top temperature

200.0 200.0

start

stop

burner fan

bottom temperature

200.0 200.0

start

stop

extraction fan

over temperature 350.0

start

4

stop

burner fan

top temperature

200.0 200.0

start

stop

burner fan

bottom temperature

200.0 200.0

start

stop

extraction fan

over temperature 350.0

start

FIGURE 18.2

stop

Zone panel.

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18. Oven operation: direct gas-fired oven

1. Start the extraction fan. 2. Start the burner air fan. 3. Set the temperature controllers to the required temperatures. At the main control panel (Fig. 18.3):

baker pacific panel live

alarm

alarm off

oven band

3.50 stop

start

band running speed

bake time

band cleaner

on

fault

oven band tension and tracking

feed end alarm

feed end trip

drive end drive end band trnsion rotation alarm trip fault fault

burners off

on purge on

complete

gas ok

E stop pressed

FIGURE 18.3 Main control panel.

1. 2. 3. 4. 5. 6. 7. 8.

Switch the panel isolator on. Check the panel live lamp is on. Set the baking time. Start the oven band. Check band running lamp is on and check band tension and tracking warnings. Check that the burner ignition is switched to ‘Off’. Check that the ‘Gas Pressure OK’ lamp is on. Check that the ‘Purge On’ lamp is on. This indicates that the 6-min purge timer has started to run to ensure that the fans clear the oven of any unburned gases. At the end of the purge period, the ‘Purge Complete’ lamp will be on.

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18.2 Lighting the burners

18.2 Lighting the burners

direct gas-fired zone

307

direct gas-fired zone

The following conditions must be met before the oven burners will light: 1. 2. 3. 4. 5. 6. 7. 8. 9.

The band is tensioned. The main manual gas valve is open. Each panel isolator is ‘On’. The extraction fans on each zone are running. This is monitored by pressure switches. The oven drive panel AC & DC isolators are on. The oven drive is started. Check the gas pressure detected by the gas pressure switch is within the set limits. If these conditions are met, the oven can be purged. The purge will last for 6 min. On completion of the purge, the main gas valves will open. When the oven purge is complete, turn burner switch to ‘on’. Those burners that have been set to ‘on’ at the ignition control unit will light (Fig. 18.4). This occurs in sequence in each zone in banks of four burners.

FIGURE 18.4

Flynn ignition control unit.

308

18. Oven operation: direct gas-fired oven

10. If any additional burners are required, select at the ignition control unit. 11. If any burner fails to light, switch the ignition control off, then on again.

18.3 Heating up/start of production 1. Set the extraction dampers to 20% open during the warm-up period. 2. Approximately 10 min before baking commences, set the extraction dampers to their baking settings. 3. Check baking time is correct. 4. Start band cleaner unit. 5. When baking temperatures are correct, start production.

18.4 Shutting down the direct gas-fired oven 1. Switch to ‘Burner Off’ at the main control panel. 2. Set the extraction dampers in each zone to fully open. 3. Keep inspection doors closed.

18.4.1 When temperature drops to 100 C 1. 2. 3. 4. 5.

Stop burner and extraction fans. Leave zone panel isolators on. Press the oven drive ‘stop’ button. Turn off the main manual gas valve. Turn off panel isolators.

18.5 In the event of power failure 1. Empty the oven by using the hand winding-out mechanism or the DC motor drive. The DC drive will start automatically on power failure. 2. Turn the ignition switches to ‘Off’. 3. Turn off the gas supply at the main manual valve.

18.6 In an emergency 1. Press the ‘Emergency Stop’ button on the main drive panel or at the oven ends.

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Further reading

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2. When any danger to personnel is removed, re-set the Emergency Stop and press the ‘Main Drive’ Start button.

Further reading Baker Pacific Ltd. Cambridge CB24 9YZ, United Kingdom. http://www.bakerpacific.net. Baker Perkins Ltd. Manor Drive, Paston Parkway, Peterborough, PE4 7AP. United Kingdom. www.bakerperkins.com.

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C H A P T E R

19 Oven operation: indirect radiant oven 19.1 Preparation 19.1.1 Baking programme Allow 40 min from start up before baking for the required baking temperatures to be reached; high baking temperatures may take longer (Fig. 19.1).

FIGURE 19.1

Baker Pacific Indirect Radiant Oven.

19.1.2 Before starting the oven 1. Check that the stripping knife is disengaged. 2. Check that the oven feed and delivery ends are clear of obstructions.

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3. Ensure that all inspection and access doors are closed. 4. Before starting the oven, ensure that the air supply is turned on for the band tension and band tracking systems. 5. Open the main supply manual gas valve. 6. Switch on the main control panel isolator. 7. Switch on the zone panel isolators.

19.2 Starting the oven 19.2.1 Controls and settings 1. Switch the panel isolator on. Check panel live lamp is on.

FIGURE 19.2 Main panel.

2. Set the baking time (Fig. 19.2). 3. Start the oven band (Fig. 19.2).

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19.2 Starting the oven

FIGURE 19.3

Zone panel.

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314

19. Oven operation: indirect radiant oven

4. Check band running lamp is on and check band tension and tracking warnings (Fig. 19.2). 5. Start oven end hood fan.

19.2.2 Lighting the burners 1. Turn on the isolator at the side of the zone panel. 2. Set the extraction damper in each zone to fully open. 3. Set the heat distribution control dampers to 50% top and 50% bottom heat. 4. Switch the extraction and circulation fans on in each zone. 5. Open the main gas supply valve on the gas train. 6. Check gas pressure lamps OK. 7. Turn burner switch to on in each zone. 8. Start purge timer. When the purge is completed ‘purge complete’ lamp will be on. 9. After the purge cycle (6 min) the burners will light. Check ‘flame ok’ lamps. 10. If the burner develops a fault, the ‘Lockout’ lamp will come on. Pressing the ‘Lockout/Reset’ button allows a repeat of the burner lighting procedure.

FIGURE 19.4 Weishaupt burner gas train.

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19.2 Starting the oven

FIGURE 19.5

315

Weishaupt burner.

19.2.3 Heating up/production 1. Set the extraction dampers to 20% open during the warm up period. 2. Set the baking temperatures for each zone. 3. Approximately 10 min before baking commences, set the extraction dampers to their baking settings. 4. Check baking time is correct. 5. Start band cleaner unit. 6. When baking temperatures are correct, start production.

19.2.4 Damper controls Refer Fig. 19.6.

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19. Oven operation: indirect radiant oven

FIGURE 19.6 Damper controls: (1) zone heating dampers for left and right zone control; (2) extraction damper; (3) turbulence controls for top and bottom.

19.2.5 Zone heating controls The zone heating dampers control the distribution of heat to the top and bottom of the zone. There are separate dampers for the heat distribution to the left and right of the zone (Fig. 19.7).

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19.2 Starting the oven

zone heating right maximum 7

zone heating left maximum 7

7

7

6

6

5

5 4

3 2

2

close bottom

1

FIGURE 19.7

0

1

5

5 4

3

6

6

4

4 3

3 2

2

close top

close bottom

1

0

1

close top

Zone heating damper controls.

19.2.6 Extraction and turbulence dampers An extraction fan draws the moist air from the baking chamber in each zone. This air can then be exhausted to atmosphere through the flue, or it can be directed to the top and bottom turbulence ducts. The damper controls allow the proportion of air extracted from the baking chamber to be divided between the flue and the turbulence ducts (Figs. 19.8 and 19.9).

FIGURE 19.8 Extraction damper control for the amount of air to be exhausted through the extraction chimney.

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19. Oven operation: indirect radiant oven

FIGURE 19.9 Damper controls for top and bottom turbulence.

19.3 Shutting down the indirect radiant oven 1. Switch to ‘Burner Off’ at the zone control panels. 2. Set the extraction dampers in each zone to fully open. 3. Keep inspection doors closed.

19.3.1 When temperature drops to 100 C 1. 2. 3. 4. 5.

Stop the circulation and extraction fans. Leave zone panel isolators on. Press the oven drive ‘stop’ button. Turn off the main manual gas valve. Turn off panel isolators.

19.4 In the event of power failure 1. Empty the oven by using the hand winding-out mechanism or the DC motor drive. The DC drive will start automatically on power failure. 2. Turn the burner switches to ‘Off’ on the zone panels. 3. Turn off the gas supply at the main manual valve.

19.5 In an emergency 1. Press the ‘Emergency Stop’ button on the main drive panel or at the oven ends.

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319

2. When any danger to personnel is removed, re-set the Emergency Stop and press the ‘Main Drive Start’ button.

19.6 Control of the heat recovery system Hot air is fed from the heat recovery collection pipe through a fan to the final zone of the oven (Fig. 19.10).

FIGURE 19.10

Baker Pacific Indirect Radiant Oven with heat recovery system.

The amount of hot air/burnt gas taken from each burner flue is controlled by dampers. One damper controls the exhaust flue and one damper controls the flow of hot air /burnt gas from the burner flue to the collection pipe. These dampers are set by the commissioning engineer to allow sufficient quantity of heat for the final zone of the oven (Fig. 19.11).

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19. Oven operation: indirect radiant oven

FIGURE 19.11 Extraction flue on the left and burner flue on the right with connection to collecting pipe for recovered hot flue gas for the heat recovery zone.

The final zone of the oven has radiant or convection ducts above and below the oven band. These ducts are divided along their length into three sections (control side, centre and non-control side). The flow of hot air into each section is controlled by a damper. These dampers may be adjusted to ensure the optimum heat balance top to bottom and across the width of the oven (Fig. 19.12).

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FIGURE 19.12

Damper controls for the final oven zone heated by recovered hot air. Separate damper controls for top and bottom and control side/centre/non-control side to balance lateral control.

Further reading Baker Pacific. Cambridge CB249YZ, United Kingdom. ,http://www.bakerpacific.net.. Baker Perkins Ltd. Manor Drive, Paston Parkway, Peterborough PE4 7AP, United Kingdom. ,http://www.bakerperkins.com..

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C H A P T E R

20 Oven efficiency 20.1 Energy use Our aim is to not only bake high-quality biscuits but also achieve the lowest cost per kg of baked product. We need therefore to consider the amount of energy required by the oven. As energy costs increase in almost every country, the efficiency of the oven is of growing importance. In certain countries such as India, fuel is very expensive and represents an important element of the total production cost. The energy used by the oven is predominantly from gas or oil fuel. Electricity is rarely used for baking now. In a gas/oil-fired oven the fuel represents around 95% 96% of the total energy usage and electricity (for powering the drive, fans and other electrical systems) about 4% 5%. The energy input to the oven is used primarily to bake the biscuit, to achieve the structure, reduce the moisture content by evaporation and to colour the biscuit. Each type of biscuit requires a certain amount of energy to achieve a good quality result. The following example is for a typical rotary moulded product which requires 0.2120 kWh (182 kcal) of energy per kg of baked product. In addition to the energy required to bake a good product, energy is lost in several ways: • • • •

by extraction of moist air from each oven zone, by heat loss through the insulation and outer covers of the oven, by the return circuit of the oven band, by heat loss from the flues from a heater module or heat exchanger in an indirect fired oven, • by hot air escaping from the oven delivery end (Fig. 20.1). In order to minimise the heat loss (wasted energy), the following oven features are important: 1. the extraction system to achieve the final moisture content required, without excessive waste of heat from the burners,

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20. Oven efficiency

FIGURE 20.1 Energy usage.

FIGURE 20.2 Rotary moulded biscuit.

2. the insulation of the baking chamber and the return band, particularly where the band temperature is high, for example when baking crackers.

20.2 Example of energy usage The following calculations of the energy balance of an oven are taken from an actual installation. Details of the product and the oven are given below, so that different data for other ovens can be substituted to make calculations of energy use accordingly. In the following energy calculations, details of the energy from the gas or oil fuel are given.

20.2.1 Product and oven Refer Fig. 20.2. Dimensions

58 3 37 mm

Weight

5.1 g

Baking time

3.8 min

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20.2 Example of energy usage

Indirect radiant oven Baking chamber

1.25 3 100 m

Zones

8 (7 burners)

Oven band

8.25 kg/m2

Extraction fans

34 m3/min (maximum)

Oven output

3200 kg/h

Refer Fig. 20.3.

20.2.2 Data from independent test results Total energy used by the oven

0.4043 kWh/kg of baked biscuits

Of this, the energy required to bake the product to the required quality

0.2120 kWh/kg of baked biscuits

Waste energy

0.1923 kWh/kg of baked biscuits

Properties and conversions Density of air at 200 C 5 0.75 kg/m3 Specific heat of air 5 1.05 kJ/kgK (at atmospheric pressure) Specific heat of water vapour: 1.89 kJ/kgK at 100 C Specific heat of water vapour: 1.95 kJ/kgK at 200 C 1 kJ 5 0.000278 kWh 1 kcal 5 0.0011622 kWh

FIGURE 20.3

Baker Pacific Indirect Radiant Oven.

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20. Oven efficiency

20.2.3 Energy to bake the product The total energy requirement to bake the product is 0.2120 kWh per kg of baked biscuit. This gives a total energy usage (gas) to bake the biscuit of: 3200 3 0.2120 5 678.4 kWh/h This is the energy utilised to bake the biscuit, form the structure, remove the moisture and colour the biscuit. The main energy requirement for baking is to create the structure and texture of the biscuits and to remove moisture in the dough. An important element in energy use is providing the latent heat of evaporation. In order to evaporate the moisture in the dough (14% of the dough weight) to a final moisture content of 3.0% latent heat for vaporisation is required. The latent heat energy required to evaporate the water from the product is 0.625 kWh/kg of water. Moisture to be removed to reach a final moisture content of 3.0% is 0.123 kg per kg of biscuits. Total moisture to be removed: 0.123 3 3200 kg 5 394 kg/h Latent heat required to evaporate 394 kg of water: 394 kg 3 0.625 5 246 kWh. This is 36% of the energy required for baking the product. Over 60% of the energy for baking the product is for the forming of the structure and texture.

20.2.4 Heat loss from extraction from baking chambers In an indirect radiant oven the extraction is for the removal of moist air only. The products of combustion are released from the burner tube and may be diverted to a heat recovery system. Volume of air extracted from each zone 34 m3/min 3 60 min 3 8 zones 5 16,320 m3/h (maximum) Estimated average extraction damper setting: 50% Estimated volume of air extracted from baking chamber 5 8160 m3/h The air extracted has been heated from ambient temperature (40 C) to an average baking temperature (200 C). This requires an energy input as follows: Weight of the air extracted per hour 5 8160 3 0.75 kg 5 6120 kg The energy required to raise the temperature of this air in the oven from 40 C to 200 C (145 C) is: 160 3 1.05 kJ/kg 3 6120 kg 5 1,028,160 kJ 5 286 kWh Energy required to raise the temperature of the water vapour from 100 C to 200 C 394 3 1.95 3 100 5 76,830 kJ 5 21 kWh Heat loss from extraction system per hour 5 307 kWh

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20.2 Example of energy usage

20.2.5 Heat loss from return band Oven band drum centres: 111 m Bandwidth: 1.25 m Band weight: 7.4 kg/m2 Specific heat of carbon steel: 0.49 kJ/kgK Band temperature at delivery end: 180 C Return band temperature at feed end: 140 C (estimated temperatures) Weight of band (on return circuit): 111 3 1.25 3 7.4 5 1027 kg Temperature loss: 180 140 5 40 C Heat loss: 0.49 3 1027 3 40 5 20,129 kJ (5.6 kWh) per revolution of the band Bake time: 3.8 min Heat loss per hour: 5.6 kWh 3 60/3.8 5 88 kWh

20.2.6 Heat loss from the insulation and outer covers of the oven Oven baking chamber

1.25 m 3 100 m

Width over top covers

2.3 m

Overall height of covers

2.0 m

Average bake temperature

200 C

Average temp in heater modules

300 C

Ave. outer side cover temperature

45 C

Ave. outer top cover temperature

55 C

Mineral wool insulation thickness

200 mm sides and 250 mm top

Mineral wool thermal conductivity (k) at baking temp.

0.08 W/m C

U value for mineral wool 200 mm thick: 0.08/0.2 5 0.4 Wm2K U value for mineral wool 250 mm thick: 0.08/0.25 5 0.32 Wm2K Heat loss from sides and top of the oven through the insulation Heat loss 5 U A dT Total area of oven sides: 100 m 3 2 m 3 2 5 400 m2 This includes 7 heater modules and baking chamber sides Area of heater modules on burner side: 13 m2 3 7 5 91 m2 Area of heater modules on non-burner side: 2 m2 3 7 5 14 m2 Total area of heater modules 5 105 m2 Total area of oven sides (less heater modules) 5 295 m2 Heat loss from sides of baking chamber sections: 0.4 3 295 m2 3 (250 C 40 C) 5 25 kW

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20. Oven efficiency

Heat loss from heater modules: 0.4 3 105 m2 3 (350 C 40 C) 5 13 kW Heat loss from top of oven: 0.32 3 100 m 3 2.3 m 3 (250 C 40 C) 5 15 kW Total heat loss through the insulation of oven sides and top: 53 kW

20.2.7 Heat loss from oven delivery end Estimated heat loss from air escaping from oven end at approx. 180 C: Estimated volume of air in the baking chamber: 1.7 3 0.8 3 100 5 136 m3 Estimated volume of air escaping per min 5 136/3.8 5 36 m3 Weight of air escaping per min 36 3 0.75 5 27 kg 27 3 60 3 1.05 kJ 3 (180 40) 5 238,140 kJ 5 66 kWh Estimated heat loss from oven delivery end: 66 kWh Estimated heat loss by radiation from oven end hood and covers: 17 kWh Total heat loss from delivery end: 83 kWh

20.2.8 Heat loss from burner flues Total energy used per hour: 0.4043 kWh 3 3200 5 1294 kWh Natural gas energy: 10.3 kWh/m3 Gas consumption per hour 5 1294/10.3 m3 5 125 m3 For combustion of 1 m3 of natural gas 9.4 11.0 m3 (average 10.2 m3) of air is required. Air volume required per hour for complete combustion (approx.) 125 3 10.2 m3/h 5 1275 m3 Total volume of products of combustion air exhausted is approximately 1400 m3/h for 7 burners Estimated average temperature of flue gases: 200 C Gas/air weight at 200 C 5 1400 3 0.75 kg/m3 5 1050 kg/h Estimated energy required to heat the combustion air: 1050 kg 3 200 3 1.05 kJ/kgK 5 220,500 kJ 5 61 kWh A proportion of this heat is available for the heat recovery zone.

20.2.9 From the calculations above, the energy consumption of the oven per hour For product

678 kWh

52%

Heat loss from extraction

307

24%

Heat loss from return band

88

7%

Est. heat loss from oven delivery end

83

6%

Biscuit Baking Technology

20.3 Comparison of oven efficiency for different oven types (based on actual installations)

Heat loss from burner flues

61

5%

Heat loss through insulation

53

4%

Est. loss from thru’ metal, fans etc.

30

2%

Total heat loss

622 kWh

48%

Total energy usage

1300 kWh

100%

329

Note: the estimated accuracy in the assumptions and base data is 6 10%. The actual efficiency delivered by the oven and confirmed by independent test was 52% (Fig. 20.4). • The overall oven efficiency is approximately 56% • Of the heat loss through the burner flues, a minimum of 50% can be recovered and used for baking in a heat recovery system (Fig. 20.5).

20.3 Comparison of oven efficiency for different oven types (based on actual installations) Refer Table 20.1.

FIGURE 20.4

Energy usage.

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20. Oven efficiency

FIGURE 20.5 Baker Pacific Indirect Radiant Oven with heat recovery system. TABLE 20.1

Energy usage for actual oven installations.

Product

Oven type

Oven size

kWh/kg of biscuits

Rotary moulded

Indirect radiant 1 HRS

1.2 m 3 100 m

0.404

Snack cracker

DGF/convection

1.2 m 3 90 m

0.477

Rotary moulded

DGF/convection

1.5 m 3 100 m

0.441

Rotary moulded

DGF/convection

1.2 m 3 60 m

0.430

Rotary moulded

DGF/cyclotherm

1.2 m 3 60 m

0.492

Rotary moulded

Indirect radiant

1.2 m 3 100 m

0.475

DGF, Direct fired oven; HRS, heat recovery system.

20.4 Calculations for the energy required to bake biscuits The energy requirements are based on the following specific heat data. Specific heat capacity data on ingredients is from http://www. engineeringtoolbox.com (Tables 20.2 and 20.3).

20.4.1 Rotary moulded biscuit Data: Production

2000 kg/h of baked biscuits (2270 kg of dough)

Baking temp. (max.)

200 C

Ambient temp.

40 C

Moisture to be removed:

270 kg/h

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20.4 Calculations for the energy required to bake biscuits

TABLE 20.2 Specific heat of ingredients for rotary moulded, hard sweet biscuits and cracker recipes. Specific heat of biscuit doughs Ingredient

Specific heat (kJ/ kgK)

Rotary moulded (Tiger)

Hard sweet (Marie)

Cracker (Ritz type)

Flour

1.59

100.0

100.0

100.0

Fat/veg. oil

1.67

32.1

21.4

11.7

Sugar

1.24

32.5

26.2

10.9

Water

4.20

9.0

20.0

29.5

Total recipe

173.6

167.6

152.1

Specific heat

1.67

1.86

2.08

TABLE 20.3 Specific heat of dry ingredients for rotary moulded, hard sweet and cracker recipes. Specific heat of dry ingredients Ingredient

Specific heat kJ/ kg K

Rotary moulded (Tiger)

Hard sweet (Marie)

Cracker (Ritz type)

Flour

1.59

100.0

100.0

100.0

Fat/veg. oil

1.67

32.1

21.4

11.7

Sugar

1.24

32.5

26.2

10.9

Total

164.6

147.6

122.6

Specific heat

1.54

1.54

1.57

Energy is required as follows: 1. The dry ingredients (total 1940 kg) must be raised in temperature from 40 C to 200 C 1940 kg 3 1.54 (sp. heat) 3 160 C 5 478,016 kJ 5 132.9 kWh/h 2. The moisture in the dough (270 kg) must be raised in temperature from 40 C to 100 C 270 kg 3 4.2 (sp. heat) 3 60 C 5 68,040 kJ 5 18.9 kWh/h 3. Energy must be provided for the latent heat of evaporation 270,000 g 3 539 cal 5 145,530 kcal 5 169.1 kWh/h

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4. The water vapour must be raised from 100 C to 200 C 270 kg 3 0.59 (density of vapour) 3 1.996 (sp. heat kJ/kg/K) 3 100 C 5 31,800 kJ 5 8.8 kWh/h The total energy requirement for baking 2000 kg/h of the rotary moulded biscuits is 330 kWh Energy required for rotary moulded biscuit: 0.164 kWh/kg of baked biscuits

20.4.2 Semi-sweet biscuit Data: Production

2000 kg/h of baked biscuits (2460 kg of dough)

Baking temp. (max.)

220 C

Ambient temp.

40 C

Water content to be removed:

460 kg/h

Energy is required as follows: 1. The dry ingredients (total 1940 kg) must be raised in temperature from 40 C to 220 C 1940 kg 3 1.54 (sp. heat) 3 180 C 5 537,800 kJ 5 149.0kWh/h 2. The moisture in the dough (460 kg) must be raised in temperature from 40 C to 100 C 460 kg 3 4.20 (sp. heat) 3 60 C 5 115,920 kJ 5 32.2 kWh/h 3. Energy must be provided for the latent heat of evaporation 460,000 g 3 539 cal 5 247,940 kcal 5 288.2 kWh/h 4. The water vapour must be raised from 100 C to 220 C 460 kg 3 0.59 (density of water vapour) 3 1.95 (sp. heat) 3 120 C 5 63,500 kJ 5 17.6 kWh/h The total energy requirement for baking 2000 kg of the hard sweet biscuits is 487 kWh Energy required for semi-sweet biscuit: 0.25 kWh/kg of baked biscuits

20.4.3 Cracker Data: Production

2000 kg/h of baked crackers (2660 kg of dough)

Baking temp. (max.)

240 C

Ambient temp.

40 C

Water content to be removed

660 kg/h

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Energy is required as follows: 1. The dry ingredients (total 2000 kg) must be raised in temperature from 40 C to 240 C 1950 kg 3 1.57 (sp. heat) 3 200 C 5 612,300 kJ 5 170.1 kWh/h 2. The water in the dough ( 660 kg) must be raised in temperature from 40 C to 100 C 660 kg 3 4.20 (sp. heat) 3 60 C 5 166,320 kJ 5 46.2 kWh/h 3. Energy must be provided for the latent heat of evaporation 660,000 g 3 539 cal 5 355,740 kcal 5 413.4 kWh/h 4. The water vapour must be raised from 100 C to 230 C 660 kg 3 0.59 (density of water vapour) 3 1.95 (sp. heat) 3 130 C 5 98,713 kJ 5 27.42 kWh/h The total energy requirement for baking 2000 kg of the snack crackers is 657 kWh/h Energy required for baking crackers: 0.33 kWh/kg of baked biscuits

References Alakali, J.S., et al., 2012. Influence of variety and processing methods on specific heat of crude palm oil. Int. J. Chem. Eng. Appl. 3 (5). Available from: http://www.researchgate.net. BizEE Software Limited, 21 Maple Crescent, Uplands, Swansea SA2 0QD, United Kingdom. , http://www.bizee.co . . Hyper Physics, 2021. Specific heat. ,http://www.hyperphysics.phy-astr.gsu.edu.. Kim, Y.S., et al., 2021. Available from: http://www.onlinelibrary.wiley.comPhysical, Chemical and Thermal Characterisation of Wheat Flour. Wiley. Sugar Engineers, 2021. Specific heat capacity. ,http://www.sugartech.com.. Testo Inc, 2021. Combustion analysis. ,http://www.testo.com.. The Engineering ToolBox, 2021. Thermal properties for water. Thermal properties for air, food and foodstuff, specific heat. ,http://www.engineeringtoolbox.com..

Biscuit Baking Technology

C H A P T E R

21 Energy for biscuit baking 21.1 Combustion data: natural gas Gas has been and continues to be the predominant fuel for biscuitbaking ovens. The development and availability of natural gas supplies have made gas the main fuel for the baking industry throughout the world. Countries where electricity was the main energy source, for example China, and countries where diesel oil was used, for example India and the Middle East, now use gas as the lowest cost energy source. The combustion of natural gas is a major source of greenhouse gases which are causing climate change. This has become a major concern throughout the world. This situation makes it essential that we seek ways to reduce the carbon footprint of the biscuit-baking industry.

21.1.1 Combustion process The combustion process is a reaction of rapid oxidisation started by the correct mixture of fuel, oxygen and an ignition source. In order for complete combustion of natural gas, excess air is supplied. The chemical reaction for natural gas combustion with 20% excess air is: CH4 1 1:20 3 2ðO2 1 3:76 N2 Þ-CO2 1 2H2 O 1 0:5O2 1 9:4N2 where CH4 is natural gas, O2 is oxygen, N2 is nitrogen, 2H2O is water vapour, and CO2 is carbon dioxide. Ref. EngineeringToolbox Air is composed of 20.9% of oxygen, 78% of nitrogen and 1% of other gases. For most applications, every 1 m3 of natural gas, approximately 10 m3 of air is required to provide complete combustion of natural gas. To ensure complete combustion of the fuel, excess air is drawn in by the burners. The combustion efficiency will increase with increased excess air, until the heat loss in the excess air is larger than the heat provided by more efficient combustion.

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When fuel and oxygen in the air are in perfectly balance and the fuel is burned completely, the combustion is said to be stoichiometric. Typical excess air to achieve the best efficiency for combustion is 10%20%. Carbon dioxide is a product of the combustion and the content in the flue gas is an important indication of the combustion efficiency. The content of carbon dioxide after combustion with excess air is approximately 10.5% for natural gas and approximately 13% for light fuel oils (Fig. 21.1).

FIGURE 21.1 Stoichiometric combustion. Source: Refer engineeringtoolbox.com//stoichiometric-combustion-d_399.html.

21.1.2 Carbon dioxide emission from burning natural gas To calculate the carbon dioxide (CO2) emission from a fuel, the carbon content of the fuel must be multiplied by the ratio of molecular weight of CO2 (44) to the molecular weight of Carbon (12) -. 44/12 5 3.7. Carbon dioxide emission from burning a fuel can be calculated as qCO2 5 cf =hf MCO2 =Mm where qCO2 is the specific CO2 emission (kgCO2 =kWh), cf the specific carbon content in the fuel (kgc/kgfuel), hf the specific energy content in the fuel (kWh/kgfuel), MC the molecular weight carbon (kg/kmol Carbon), MCO2 the molecular weight carbon dioxide (kg/kmol CO2).

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Emission of CO2 from methane, natural gas is given below: Specific carbon content

kgc/kgfuel

0.75

Specific energy content

kWh/kgfuel

15.4

Specific CO2 emission

kgCO2 =kgfuel

2.75 (amount of fuel basis)

Specific CO2 emission

kgCO2 =kWh

0.18 (amount of energy basis)

Note: Heat loss—55%75%—in power generation is not included in the numbers. Reference: Engineering Toolbox Combustion of fuels—carbon dioxide emissions. From http://www.engineeringtoolbox.com/co2-emission-fuels-d_1085html.

21.2 The biscuit industry carbon footprint 21.2.1 Climate change and greenhouse gases Greenhouse gases in the atmosphere absorb heat energy from the sun and emit it, keeping the earth’s surface and lower atmosphere warm. Greenhouse gases include carbon dioxide, water vapour, methane and nitrous oxide. The biggest contributor to the warming of the climate is carbon dioxide, CO2. Since pre-industrial times the atmospheric concentration of CO2 has increased by over 40% and methane by over 150%. More than half of this increase has occurred since 1970. Methane is an important greenhouse gas which leaks during industrial processes, particularly fossil fuel use and distribution and agriculture. Work on reducing air pollution is valuable and can lead to lasting cuts in methane emissions. Water vapour is also a potent greenhouse gas, but it has a short lifetime and is an amplifier, not a driver of climate change. Human activities currently emit an estimated 10 billion tonnes of carbon each year, mostly by burning fossil fuels. Reference: The Royal Society http://www.royalsociety.org The biscuit industry now uses gas as the fuel for baking in almost every country. Natural gas is now widely available and economic. However, this gives our industry a large carbon footprint. It will attract pressure in many countries to reduce the use of gas, by using electricity from renewable sources and improving efficiency. Efficiency can be improved by • effective insulation of the baking chambers and return band, • burner specification and adjustment for low CO2 emission, • baking chambers of minimum cross section to increase radiation from the surfaces, • heat recovery systems for indirect-fired ovens,

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• using the extraction from the flues for heating factory services such as heating water, and • using hot flue gases to pre-heat combustion air.

21.2.2 Energy usage for baking The following table indicates some typical values for energy usage for baking. Energy for baking kWh/kg (excluding oven losses)

Energy for baking kWh/kg (including est. losses)

Short dough biscuits

0.2121

0.404

Semi-sweet biscuits

0.2502

0.477

Crackers

0.3402

0.646

Product type

1

From actual installation. From calculations see Chapter 20.

2

21.2.3 Consumption of gas for baking Density

0.68 kg/m3

Density at baking temperature

0.4 kg/m3

Heat value of burning natural gas (methane)

4255 MJ/kg (11.615.3 kWh/kg)

Average energy per kg of gas

13.45 kWh/kg

Refer http://www.world.nuclear.org.

The calorific value, density and energy for natural gas vary with the source, process and delivery. The values above are from the sources listed under references. Energy usage

kWh/kg

Natural gas consumption for baking 1 tonne of biscuits

Short dough biscuits

0.404

30.0 kg of gas

Semi-sweet biscuits

0.477

35.5 kg of gas

Crackers

0. 646

48.0 kg of gas

Average power requirement per tonne of product range 509 kWh. Average gas consumption per tonne 37.8 kg.

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21.2.4 The carbon footprint The combustion of 1.0 kg of natural gas produces 2.75 kg of CO2 and 0.18 kWh of energy (http://www.engineeringtoolbox.com). The average production of CO2 for one tonne of product range (short dough/semi-sweet, cracker) is 37.8 3 2.75 5 104 kg. CO2 emissions: 104 kg/t of product range A bakery with three production lines producing a total of 50 t per 8 h shift and 20 shifts a week will produce approximately 1000 t of biscuits per week. The CO2 emissions will be approximately 104,000 t per week and over 5,200,000 t per year. Biscuit consumption and CO2 emissions in several countries.

Population (M) (2017)

Per capita consumption (kg/year) (2014/2015)

Total est. consumption (‘000 T/year)

Gas consumption (‘000 T/year)

Total est. CO2 emissions (‘000T/year)

Argentina

44

12.44

547

20.7

56.9

Brazil

208

6.05

1258

47.5

130.6

China

1421

2.23

3169

119.7

329.2

Italy

61

10.5

640

24.2

66.5

Nigeria

201

2.36

474

17.9

49.2

United Kingdom

67

13.6

911

34.4

94.6

United States

325

6.91

2246

84.9

233.5

In these countries the total population of 2327 million produce 960,500 t of CO2 emissions each year from biscuit production. Per capita emissions: 0.413 kg/year. The total global CO2 emissions in 2016: 35,753,305,000 t. The world population is 7.46 billion. Per capita CO2 emissions: 4.79 t. http://www.worldometers.info/co2-emissions.

21.2.5 Energy sources for biscuit baking The current energy source for biscuit-baking worldwide is gas. The option in some countries is fuel oil. However oil has a higher CO2 emission rate than gas, 3.15 kgCO2 =kgfuel compared to 2.75 kgCO2 =kgfuel for gas. Electricity has substantial advantages for baking, but currently is expensive and the main generation systems involve substantial CO2 emissions. Fossil fuels have been the cheapest source of power for generating electricity. However, burning fossil fuels for generating electricity and heat is the largest source of greenhouse gases, causing 30% of global emissions.

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21.3 Generating electricity from renewable energy sources The concern over climate change and the urgent need to reduce carbon emissions has led to the rapid development of renewable energy sources, solar, hydropower, wind and biomass. In addition, nuclear power is an important source for the generation of electricity. The methods of the generation of electricity have changed during the last 10 years and now energy from some renewables is less costly than energy from new fossil fuel sources. LCOE (Levelised costs of energy): based on the cost of building the power plant and the costs of fuel and operation during the plants lifetime. USD/MWh

2009

2019

Solar photovoltaic

359

40

Solar thermal tower

168

141

Nuclear

123

155

Onshore wind

135

41

Coal

111

109

Gas peaker

275

175

Gas

83

56

Refer http://www.ourworldindata.org.

Electricity costs from solar fell 13% year-on-year reaching USD 0.068/kWh in 2019. Onshore and offshore wind costs fell about 9% year on year to USD 0.053/kWh and USD 0.115/kWh respectively for newly commissioned projects. Renewables made up 26.2% of global electricity generation in 2018. It is expected to rise to 45% by 2040. Over half of all utility-scale renewable capacity additions in 2019 achieved lower costs than the cheapest equivalent new coal plant (http://www.c2es.org; http://www.energypost.eu).

21.3.1 Power generation costs for renewable energy USD/kWh

2010

2021

Solar photovoltaic

0.37

0.05

Solar concentrated solar power

0.35

0.07

Offshore wind

0.16

0.13

Onshore wind

0.08

0.05

Refer http://www.energypost.eu.

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The price of generation from onshore wind and solar PV-generated power have both fallen below USD 0.05/kWh. Fossil fuelpowered generation usually costs between USD 0.05/kWh and 0.18/kWh. These developments will continue based on concerns over climate change and the need to reduce carbon emissions. This will affect the options for energy for biscuit baking (Fig. 21.2).

FIGURE 21.2

After Lazard.

21.3.2 Development of electricity generation from renewables Renewable energy became the biggest source of electricity in the European Union in 2020 reaching 38% of the total electricity generated. For several individual countries, it is now the main source of electricity, including United Kingdom, Germany and Spain. In United Kingdom 54% of electricity came from low-carbon sources. In 2020 renewable energy sources accounted for 12% of the total energy consumption and 20% of electricity generation in the United States. Japan’s government has pledged to increase renewable sources, solar and wind, for electricity generation from 10% in 2018 to 22%24% by 2030. The Renewable Energy Master Plan (REMP) for Nigeria seeks to increase the supply of renewable electricity from 13% of total electricity generation in 2015 to 23% in 2025 and 36% by 2030. Renewable electricity would then account for 10% of Nigerian total energy consumption by 2025. REMP targets higher electrification rates, from 42% in 2005 to 60% in 2015 and 75% by 2025.

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In a number of countries in Asia Pacific, Latin America and Africa energy from biomass contributes a significant source of energy with lowcarbon dioxide emissions. The most common biomass materials used for energy are plants, such as corn and soy and wood. The energy from these materials can be burned to create heat or converted into electricity. Some coal-fired power stations are now being converted to burn biomass (Fig. 21.3).

FIGURE 21.3 Increase in energy from renewables 201925. Renewables will become the largest source of energy by 2025, surpassing coal. Source: From International Energy Agency. http://www.iea.org.

21.3.3 Future developments for biscuit baking It is predicted that electricity will in the future be a preferred energy for many industries, based on competitive costs with current gas supplies and the need to reduce reliance on fossil fuels. In addition, electricity is a clean and easily controlled energy source. Electric baking ovens have the following features: • Radiant heat transfer which is penetrative and achieves optimum volume and texture of the products. • Clean energy that does not contaminate the products or the baking environment. There are no products of combustion. • Dry heat which is efficient in reducing moisture content. Steam application and turbulence systems provide humidity as required by the baking process. • Electric heaters are easily and accurately controlled. • Minimum oven maintenance is required.

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21.4 Solar energy 21.4.1 New biscuit bakeries Modern biscuit bakeries have long flat-roofed production areas. Fig. 21.4 is an example of modern bakery design. New bakeries now often have production areas of around 150 m 3 30 m, 4500 m2. This area could be used for solar panels (Fig. 21.5).

FIGURE 21.4

New PT Mayora Indah bakery in Indonesia with solar panels.

FIGURE 21.5

Solar panels. Source: Photo by MICHAEL WILSON on Unsplash.

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21.4.2 Solar energy for a new bakery A bakery roof of 4,500 m2 could support 2000 solar panels of 96 cells and 350 W capacity for each panel. The panel size is 1.90 m 3 1.0 m. Energy 5 solar panel watts 3 average hours of sunlight per year 3 0:75

0.75 is the typical efficiency factor. Hours based on mid-Europe: 2000 h per year Calculation: 350 W 3 2000 h 3 0.75 5 525,000 W per year per panel 525 kWh/panel 3 2000 panels 5 1,050,000 kWh per year Vivint Solar: http://www.vivintsolar.com Power requirement for a production line: Average power requirement for producing 1000 kg of cracker, semisweet and short dough biscuits: 509 kWh Our 2000 solar panels would power the production line for approximately 2000 h. Average hours of sunlight per year: • • • • • • •

Europe: Paris 1660, Rome 2500 The United States: Chicago 2508 Brazil: Sao Paolo 1948 Asia: Bombay 2680, Jakarta 2975 Africa: Lagos 1885, Johannesburg 3182 China: Shanghai 1874 Australia: Sydney 2426

Further reading CEIC Data, 2021. ,http://www.ceicdata.com.. Center for Climate and Energy Solutions, 2021. ,http://www.c2es.org.. Energy Post.eu, 2021. ,http://www.energypost.eu.. Global Solar Atlas, 2021. ,http://www.globalsolaratlas.info/map.. IN HABITAT 909N, 2021. El Segundo, CA. ,https://inhabitat.com.. International Energy Agency, 2021. ,http://www.iea.org.. IPCC, 2021. Intergovernmental Panel on Climate Change. ,http://www.unfoundation. org/climate/panel.. Lazard, 2021. ,http://www.lazard.com.. NFPA Committee Input No. 48  NFPA 872012, 2021. ,http://www.nfpa.org.. Nuclear Energy Agency, 2021. ,http://www.oecd-nea.org/lcoe.. Our World in Data, 2021. ,http://www.ourworldindata.org.. Photonic Universe, 2021. ,http://www.photonicuniverse.com.. Photovoltaic Software, 2021. ,http://www.photovoltaic-software.com.. Statista, 2021. ,http://www.statista.com.. Testo Inc, 2021. Applications guide rev. 1.0. 2006. ,http://www.testo-international.com..

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Further reading

345

The Engineering ToolBox, 2021. ,http://www.engineeringtoolbox.com.. Thermowatt DhE, 2021. ,http://www.thermowatt.com.; ,http://www.dhesrl.com.. UK Power, 2021. ,http://www.ukpower.com.. Vivint Solar, 2021. ,http://www.vivint.com.. Watlow, 2021. ,http://www.watlow.com.. World Bakers, 2021. ,http://www.worldbakers.com..

Biscuit Baking Technology

C H A P T E R

22 Oven inspection and audit It is recommended that each oven is given a complete inspection and audit every 12 months. The annual inspection and audit will support the preventative maintenance programme and help to ensure excellent oven performance, economy and long life.

22.1 Oven performance 22.1.1 Output • Check product specification and baking time to calculate oven output capacity in kg/h • Check actual output of packed, saleable product over 8 h shift (Fig. 22.1)

FIGURE 22.1

Packing table.

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• Check downtime/causes/trends in oven output • A log should be maintained of problems causing downtime. Any repetitive problems or trends in output can be identified, and appropriate action taken.

22.1.2 Product specification/compliance Check 10 biscuits from each lane every hour for compliance to the product specification. Check variation across the width of the oven and variation with time: • • • •

Biscuit weight Biscuit size (length, width, diametre) Colour (compare to standard samples) Moisture content

Identify any quality problems with Quality Control staff, such as ‘checking’, shelf life and packaging issues (Figs. 22.2 22.4).

FIGURE 22.2 Esa Precision Scale from Brecknell Scales.

Biscuit Baking Technology

22.1 Oven performance

FIGURE 22.3

Sartorius moisture analyser (MA).

FIGURE 22.4

Konica Minolta CM-5 colour spectrophotometer.

22.1.3 Energy usage • Check fuel consumption over the 8 h shift (gas/oil usage) • Calculate energy in kW/kg of baked biscuits and compare with target energy usage (Figs. 22.5 and 22.6)

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FIGURE 22.5 Bell Flow Systems fuel and oil flow metre MX09F.

FIGURE 22.6 Bell Flow Systems MTM gas turbine metre.

Energy usage for different biscuit types is given below as a guide. The ‘energy required to bake the product’ is the energy requirement for heat input to convert the dough pieces to baked biscuits, and this

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22.2 Oven band

excludes heat loss from the oven. The ‘Total energy required’ assumes a typical biscuit oven efficiency including heat loss. The final column ‘Typical range of energy required’ is a guide for comparison with actual energy usage. If the energy used exceeds this range, investigation is needed to improve the oven efficiency (Table 22.1). TABLE 22.1

Energy usage guide.

Energy usage guide Biscuit type

Example

Energy required to bake product (kWh/kg)

Total energy required included heat loss from the oven

Typical range of energy required for baking (kWh/kg)

Rotary moulded

0.17

0.33

0.33 0.36

Hard sweet

0.25

0.48

0.48 0.53

Crackers

0.34

0.67

0.67 0.74

22.2 Oven band Check the following: • Band condition (edge damage, cleanliness) (Figs. 22.7 and 22.8)

FIGURE 22.7

Wire-mesh band.

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FIGURE 22.8 Band cleaner.

• Band support skids/rollers (all rollers free and rotating, skids and rollers clean) (Figs. 22.9 22.11)

FIGURE 22.9 Skid bars.

• Band tracking (band wander limit switch settings to detect 6 10 mm band deviation)

Biscuit Baking Technology

FIGURE 22.10

Roller band support.

FIGURE 22.11

Tracking system.

• Check alarms and shut down at the set point (over 25 mm deviation) • Band tension: check pneumatic system, air pressures, check actual tension applied compared to calculated requirement for the band type and oven length • Check oven drum support bearings and slides. Check lubrication of slides (Fig. 22.12)

FIGURE 22.12

Oven tension end.

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22. Oven inspection and audit

• Oven drive: check belts and chains for wear and tension • Check gearbox and drive transmission lubrication • Check bearings (Figs. 22.13 and 22.14)

FIGURE 22.13 Oven drive end.

FIGURE 22.14 Oven drive end.

• Alarms: check all alarm and safety circuits for band rotation, tracking and tension • Emergency drive/UPS (shut down power and check UPS system operates to empty the oven of biscuits) (Fig. 22.15)

Biscuit Baking Technology

22.3 Baking chamber

FIGURE 22.15

355

Oven main drive and DC motor.

22.3 Baking chamber • Length and zone configuration • Insulation/temperatures of outer covers • Check temperatures and heat loss at the oven ends (temperatures of outer covers should not exceed ambient 110 C) (Fig. 22.16)

FIGURE 22.16

Example of diagram showing checks of the outer temperatures at the

oven delivery end.

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• Cleanout doors/condition inside the baking chamber • Check for broken biscuits which could cause a fire • Check for distortion and leaks in the baking chamber structure (Fig. 22.17)

FIGURE 22.17 Cleanout door for baking chamber.

• Extraction system/fans/pressure switches • Check fan rotation, clean filters, bearings and impellers • Check pressure switches setting and operation (Figs. 22.18 and 22.19)

FIGURE 22.18 Extraction fan. Biscuit Baking Technology

FIGURE 22.19

Pressure switch.

• Oven end hood and extraction • Check extraction fan/heat loss around delivery end (Fig. 22.20)

FIGURE 22.20

Oven delivery end.

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22.4 Gas and oil trains Check the following (Figs. 22.21 and 22.22):

FIGURE 22.21 Gas train.

FIGURE 22.22 Gas train for Weishaupt burner.

• • • • •

Gas train installation/connections/gas filters Main gas supply pressure Main gas valve operation/pressure gauges/zero governor Gas proving system to detect any gas leaks Check the gas and air header pipes and flexible pipe connections

22.5 Gas burners 22.5.1 Burners: direct gas-fired ovens • Check burner strips for dirt/blockages (Fig. 22.23)

Biscuit Baking Technology

22.5 Gas burners

FIGURE 22.23

• • • •

DGF oven. DGF, direct gas-fired.

Check ignition/flame monitor units Adjust electrode gaps Check flames: short blue flames (nor long, yellow, lazy flames) Adjust gas/air mix as required (Fig. 22.24)

FIGURE 22.24

Flynn gas burner.

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22. Oven inspection and audit

22.5.2 Burners: indirect-fired ovens • • • • •

Check fuel supply/filters Check combustion air fan/filter/pressure switches Check operation of manual and solenoid valves Check gas governor as pressure gauges Check pressure in burner tube with a manometer (should be negative pressure/positive pressure may indicate a leakage in the heat exchanger) • Check burner ignition • Check flame shape and stability • Check Weishaupt Combustion Manager/diagnostics (Figs. 22.25 and 22.26)

FIGURE 22.25 Weishaupt gas burner.

Biscuit Baking Technology

22.6 Temperature and humidity control systems

FIGURE 22.26

361

Honeywell Maxon dual fuel burner installation.

22.6 Temperature and humidity control systems A data logger may be used to check the temperature profile and humidity in the oven and identify problems of variation across the width of the oven and variation from set temperatures in each zone.

22.6.1 Heat flux Heat transfer depends not only on temperature, but is also affected by other conditions such as air movement. In an oven, the heat energy will be transferred to the dough piece by radiation, conduction from the oven band and convection. In principle, heat flux sensors measure radiant, conducted and convective heat transfer. This gives a more complete understanding of the rate of heat transfer to the dough pieces than measuring temperature alone. Heat flux is the rate of heat energy transferred to a given surface and is measured in watts per square metre (W/m2). (1 W/m2 5 0.86 kcal/h/m2). This is expressed as: Qv 5 Q=A where Qv is a heat flux (W/m2), Q is a heat transfer rate (W/h) and A is an area (m2).

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22.6.2 Measurement of heat flux Data loggers can record the rate of heat transfer, taking into account temperature, air velocity and conduction. They utilise the direct method of heat flux sensing (surface mounted heat flux sensors). When heat passes through the heat flux sensor, a temperature gradient is developed across it. The difference in temperature is detected by a thermopile in the heat flux sensor. The sensor head is connected to a data logger with a high memory capacity. The data logger is lightweight and portable with battery power. It has a dual sensor head enabling top and bottom heat flux measurements to be made simultaneously with recording air temperature. The data logger will produce a graph showing both air (baking) temperature and heat flux at top and bottom of the sensor. Normally it can be seen that the air temperature shows a (relatively) continuous curve. However in a convection oven, the heat flux traces are more complex. They show very low dips at the end of each zone and a spiky trace reflecting the convection air jets impinging on the sensor through each oven zone. The SCORPION 2 from Reading Thermal monitors four parameters: 1. 2. 3. 4.

Temperature of air, band and product core Airflow Energy transfer Humidity

The sensor is passed through the oven with the product. The data is collected, and the profiles downloaded from the Data logger to a PC for analysis with SCORPION Software.

22.6.3 Baking temperature and humidity Our main baking controls (direct gas-fired, indirect radiant and convection ovens) are by temperature and humidity. Zone temperatures and extraction settings are set to match the required baking profile and to control the heat input from the burners to maintain the set baking temperatures. The extraction fans control the humidity. The baking temperatures through the oven and across the width of the oven band and the humidity data are therefore a valuable guide to the performance of the oven and a good starting point for trouble shooting problems such as uneven colour and moisture content (Fig. 22.27).

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FIGURE 22.27

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Watlow F4T data logger and SpecViewSCADASoftware.

The Watlow F4T all-in-one optional capabilities include: integrated PID controller, data logger with encrypted files, graphical trend charts, limit controller, solid-state relays, timers, counters, PLC math and logic, panel switches and lights (softkeys) all connected.

22.7 Controls and electrical panels • Check all temperature controllers are operational, including overtemperature controllers • Check variation in set temperatures and actual temperatures on the controllers • Check PID settings and adjust as required • Check thermocouple positions and wiring • Check all damper controls • Check cleanliness and vacuum clean • Check all wiring secure in panels and trunking • Operate safety systems and alarms • Check all E-stops function correctly

22.8 Reporting The inspection and audit will provide a complete and detail report on all aspects of the oven performance as outlined above. The aim is to 1. secure the best product quality, 2. achieve the optimum oven efficiency in terms of cost per kg of baked biscuits,

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3. reduce downtime and achieve the highest possible production efficiency, 4. support development of preventative maintenance and a programme of equipment and operational improvements.

Further reading Avery-Weigh Tronix. 1000 Armstrong Drive, Fairmont, MN 56031-1439, USA, www.averyweightronix.com Brecknell Scales. Foundry Lane, Smethwick, West Midlands, B66 2LP, United Kingdom, www.brecknellscales.co.uk Baker Perkins Ltd, Manor Drive, Paston Parkway, Peterborough PE4 7AP, United Kingdom, www.bakerperkins.com Bell Flow Systems. Unit 7, Swan Business Centre, Osier Way, Buckingham, Bucks, MK18 1TB, United Kingdom, www.bellflowsystems.co.uk Digitron. British Rototherm Company Ltd. Kenfig Industrial Estate, Margam, Port Talbot, SA13 2PW, United Kingdom, 2021, www.digitron.com Endress 1 Hauser Ltd. Floats Road, Manchester M23 9NF, United Kingdom, www.uk. endress.com Eratec. 80 rue Rene´ Descartes, 38090 Vaulx-Milieu, France. www.era-tec.com Flowquip Ltd. Riverside, Canal Road, Sowerby Bridge, HX6 2AY, United Kingdom, www. flowquip.co.uk Flynn Burner Corp. 225 Mooresville Blvd. Mooresville NC 28115, USA. www.flynnburner. com Halifax Fan. Mistral Works, Unit 11, Brookfoot Business Park, Elland Road, Brighouse, West Yorkshire, HD6 2SD, United Kingdom. www.halifax-fan.co.uk Honeywell Thermal Solutions. 201 East 18th Street, Muncie, Indiana, IN 47302, USA, www.honeywell.com IPCO Sweden AB. 2453-B Va¨stra Verken, 81181 Sandviken, Sweden, https://ipco.com Konica Minolta Inc. JP TOWER, 2-7-2 Marunouchi, Chiyoda-ku, Tokyo 100-7015, Japan. www.konicaminolta.com Reading Bakery Systems. 380 Old West Penn Anenue, Robesonia, Pennsylvania 19551, USA, www.readingbakery.com Sartorius Stedim UK Ltd. Longmead Business Centre, Blenheim Road, Epsom, Surrey KT19 9QQ, United Kingdom, www.sartorius.com Vo¨gtlin Instruments GmbH. St. Jakob-Strasse 84, 4132 Muttenz, Switzerland, www.vo¨gtlin. com Watlow. Yarbrough, Austin, TX, USA. www.watlow.com Weishaupt Corp. Max Weishaupt GmbH, Max-Weishaupt-Straße 1488477 Schwendi, Germany. www.weishaupt-corp.com

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C H A P T E R

23 Oven maintenance 23.1 Preparation Before carrying out any maintenance, ensure that the equipment is isolated and that all power and fuel supplies are shut down: • Electrical supply • Pneumatic supply • Fuel supply Ensure that all lock out devices have been activated Ensure that the oven has cooled down to a safe working level (Fig. 23.1).

FIGURE 23.1 Baker Pacific hybrid oven.

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23.2 New equipment After the oven has been running for 1 month, check that all the nuts, screws, setscrews and taper pins are tight. These should then be checked over periodically. Include all electrical terminals in these checks.

23.3 Routine maintenance Regular maintenance is essential to prevent expensive stoppages of production. It is recommended that regular preventative maintenance be carried out and any items requiring attention dealt with as soon as possible to prevent any further damage. Maintenance schedules are set out below.

23.3.1 Safety devices All safety devices must be checked for correct operation at weekly intervals.

23.4 Mechanical components 23.4.1 Welded components Where components are subject to stress and load, it is important that they are checked regularly (weekly) for integrity and general condition of the welds.

23.4.2 Driving chains and belts Driving chains and belts should be checked regularly (weekly) for general condition and tension, adjustment being made if necessary.

23.4.3 Motors and drives Regular attention (monthly) should be paid to the mountings to ensure they have not worked loose, and that the drive alignment is correct. Adjust and tighten if necessary.

23.4.4 Steam lines and fittings Particular care must be taken to ensure any steam leaks are located and repaired as soon as possible. Steam is dangerous and presents the risk of injury to personnel working in the area.

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23.4.5 Air lines and fittings Regular inspection (monthly) of the pneumatic system should be made and any leakages corrected. Any air lubricators should be topped up with lubricant, and filters should be checked and cleaned.

23.4.6 Seal and gaskets Replace any seals or gaskets that show signs of deterioration or damage. When assembling, ensure that any nuts, etc. are tightened evenly so that the seal and housing are drawn square to the shaft.

23.4.7 Bearings When replacing a bearing, ensure that it is correctly lubricated. Note that many bearings are sealed units requiring no further lubrication.

23.4.8 Conveyor belts Conveyor belts should be checked regularly (weekly) for general condition. The belt tension and belt tracking should also be checked at the same time to ensure maximum belt life. Where automatic belt tensioning and tracking systems are fitted, they should be checked for correct operation.

23.4.9 Oven band tension The oven band tension and tensioning system should be checked every week. A wire-mesh band should be only just taut enough for the drum to drive it; excessive tension will stretch the band unduly and cause a reduction in width. The oven feed end incorporates the tension gear for the oven band. The tension gear compensates for changes in length of the oven band due to temperature variations or band stretch. Check each week while the oven is at baking temperature, that the limit of travel of the feed end drum has not been reached its limit and that no slip occurs on the driving drum at delivery end. Eventually, a wire band will stretch up to its final operating length. Before the drum reaches the limit of its travel, the band must be shortened by cutting out a section and re-making the joint.

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23.4.10 Pneumatic tension arrangement The movement of the feed end drum is controlled by air cylinders. A pre-set air pressure acts on the cylinder pistons and keeps the band at the correct tension at all times. Incorporated in the pneumatic systems is a relief valve which will relieve the excessive pressure that tends to build up at the end of a production run as the oven cools and the band contracts. A non-return valve is also fitted to prevent the fall of cylinder air pressure should the main air supply fail.

23.4.11 Band pressure switch An air pressure switch ensures that air at the correct pressure is available before the oven drive can be started. The air pressure regulator, relief valves and pressure switch have been set by the commissioning engineer to suit the size of oven and type of the band. No subsequent re-adjustments should be necessary.

23.4.12 Oven band tracking Automatic tracking rollers are fitted at each end of the oven before the end drums. These are pneumatically operated when the band wanders and engages one of the limit switches. The band wander warning switches and the free movement of the assembly should be checked weekly. The pneumatic equipment and free movement of the tracking rollers should also be checked weekly. The vertical side guide rollers have been set clear of the band, and there should never be continuous contact between the band and the guide rollers otherwise the edge of the band may be damaged. After the initial running and commissioning period, very small adjustments to two or three rollers supporting the return band under the oven should be sufficient to track the band correctly. Any tracking adjustments should be made with the band running at slow speed, and it will take two or three complete revolutions of the band before the adjustments take effect.

23.4.13 Bearings for oven band support rollers Each oven band roller is supported on pillow block bearings. Check the bearings regularly for free running.

23.4.14 Explosion panels Explosion panels are incorporated in the oven crown to minimise the damage caused by an explosion. It is recommended that the expendable

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items are kept in stock as spare parts. Every year check the explosion panels and replace any damaged parts.

23.4.15 Oven flues Periodically inspect the exterior sections, roof fixings, weather capes and rain hoods for security and state of repair. Periodically inspect the flanged joints to ensure that a gas tight seal is being maintained. Renew any defective joints, using a standard joint ring made from a compressed fibre. Should welding be necessary due to repairs or modifications to the equipment use an anti-acid grade stainless steel type of rod.

23.4.16 Pulleys for fans Fan and motor pulleys which are fitted with taper-lock securing bushes should be checked with reference to the supplier’s instruction sheet for details of the removal and fitting instructions.

23.4.17 Fans Any tendency to noisy running should be investigated. It may be due to the bearings, which should be replaced or lubricated, or to dirt buildup on the impeller, which should be cleaned.

23.5 Electrical maintenance 23.5.1 General Components with moving parts should be inspected at intervals related to their frequency of operation. Pitting of electrical contacts after a short period of service is normal bedding-in and is not detrimental to their operation. Modern contacts have a special finish and must not be ‘dressed’. Silvered contacts will oxidise and become black and should not be polished since this would remove some of the coating.

23.5.2 Cleaning Every 6 months control panels should be cleaned using a vacuum system. If this is not available, use a hand blower or a compressed air line. Avoid excessive use of compressed air because entrained moisture could be harmful.

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23.5.3 Relays The normal mechanical life of relays and contactors is approximately five million operations. It is recommended that those components which are subjected to frequent switching be checked and, if necessary, replaced after approximately five million operations. Relays not subjected to frequent operation, for example, those in alarm and safety circuits should be inspected and tested regularly (weekly).

23.5.4 Inspection schedule for relays Refer Table 23.1. TABLE 23.1

Inspection schedule.

Type

Frequency

Action

Low duty

Operated less than once an hour

Inspect every 6 months

Normal duty

Operated more than once an hour but less than once per minute

Inspect every 3 months

High duty

Operated more than once a minute

Inspect every month

Safety duty

N/a

Inspect and test weekly

23.5.5 Temperature controllers It is recommended that arrangements are made for the periodic servicing of the equipment according to the manufacturer’s instructions.

23.5.6 Connections and leads Every 6 months check all terminals for tightness, security and that they are safe. Check that all insulating and safety shrouds are securely in place and in good condition. Check that flexible cables have freedom of movement, particularly on devices which move frequently. Check that the insulation of cables has not been cracked or worn by moving parts, either mechanical or by opening doors or covers.

23.5.7 Fuses If one power fuse breaks on a three-phase supply, then the other two should be renewed also. Always replace fuses on a three-phase systems as a set of three.

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23.5.8 Earth leakage protection devices Where these are installed, a regular (monthly) operation check should be carried out.

23.5.9 Clutches and brakes Refer to the manufacturer’s instructions for inspection requirements with due regard to the frequency of operation.

23.5.10 Transistor/solid-state devices The life of transistor and solid-state devices is indefinite. In the event of failure of a transistor device, circuit or component, replace the complete unit or plug-in board.

23.5.11 Limit switches The actuator should be regularly inspected (monthly) for freedom from wear or damage. The operation and alignment should be checked and adjusted if needed. Inspect the rod or roller and any rubber seal around the plunger actuator. Renew the switch after approximately one million operations.

23.5.12 Proximity detectors (inductive or capacitive) These are solid-state devices and require no periodic maintenance, except to check that the mounting is secure with the correct sensing gap and to wipe them clean. The frequency of cleaning will depend upon operational conditions.

23.5.13 Plug-in timers The plug-in timer is a transistor unit and contains a relay similar to a normal plug-in relay with similar life and maintenance requirements.

23.5.14 Battery safety Refer to manufacturers data. The gases that can be emitted are explosive, and the battery area must therefore be well ventilated. All forms of external ignition, such as gas torches and welding equipment, must not be used in the vicinity of batteries. Always wear safety goggles when working on batteries.

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Battery acid on the skin must be washed with liberal amounts of clean water. A dilute sodium bicarbonate solution can be used as an eye-wash for sulphuric acid. For potassium hydroxide, use a weak solution of vinegar. Otherwise, bathe with fresh water. Always consult a doctor after using an eye-wash. Cells and batteries are always live, even when the electrolyte has been totally lost through container breakage or spillage. Keep metal objects well away from cells as sparks may cause an explosion. Insulated spanners must be used when working on a battery. Do not remove a cell from the circuit without first isolating the load and charger.

23.6 Maintenance schedule 23.6.1 Each day 1. Drain the filter bowl of the pneumatic band tensioning arrangement. 2. Empty and clean the scrap trays at the feed and delivery ends. 3. Check the oven band tracking and tension equipment.

23.6.2 Each week 23.6.2.1 Driving belts Carefully examine all driving belts for correct tension and wear. Refer to maker’s instructions for details. Toothed timing belts drive the band cleaner if fitted. 23.6.2.2 Fan filters Remove and wash the combustion air fan filters. Replace when dry. 23.6.2.3 Inspection and access doors Examine the seal between the door and its frame and rectify any defect which may cause damage to the structure and the paintwork. 23.6.2.4 Oven lamps Keep the oven lamp glasses clean and regularly examine the bulb and replace it if it becomes dis-coloured. Examine the holder and the flexible cable. 23.6.2.5 Dampers Continuous production of a small range of products requiring similar control settings often leads to damper assemblies remaining unaltered

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for long periods. Under such conditions, dampers may become hard to adjust, or in extreme cases completely locked. Operate every heat control and extraction damper throughout its full working range to ensure that they work freely. 23.6.2.6 Emergency drive Run the emergency drive and check the battery. 23.6.2.7 Oven ignition Inspect and reset the spark gap to 3.5 mm. Check for cracks in the ceramics. 23.6.2.8 Oven band Check the condition of the oven band and that the tension and tracking equipment is operating correctly.

23.6.3 Every 12 months 23.6.3.1 Burners and gas equipment Zero-pressure regulator inspect diaphragms (main and middle) and valve. Check that the impulse tube is not blocked. • • • •

Have the burners serviced by a specialist. Remove any build-up of dirt within the burner nozzles. Check flexible air and gas hoses for any leakage. Replace where necessary. Inspect high tension ignition leads. Replace if necessary.

23.7 Oven cleaning Regular cleaning of the inside of the oven must be carried out as a build-up of material can constitute a fire or explosion hazard. The oven is designed for easy cleaning using an industrial vacuum cleaner with a flame proof motor. Check oven band vibration, especially at the delivery end, where the product is lighter and less adhesive to the band, should be attended to as a matter of urgency as this will tend to bounce product off the band. Toppings applied before baking, such as salt and sugar should be carefully monitored and recovery and surplus removal systems put in place. Caution Do not attempt to clean inside a hot oven The top of the oven should be vacuumed periodically. All outer sheets should be wiped down periodically. Use a damp cloth and do not over wash as water may seep into the insulation.

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Motor and fan covers should be periodically vacuumed. Do not wash as water may seep into the motor or fan components. Gas filters. A filter may be incorporated in the gas supply to each burner and in some instances in the supply to the oven. The elements will require cleaning or replacement at intervals dependent entirely upon the operating conditions of a particular installation and can only be determined by experience. Cleaning of the element can, in most cases, be carried out satisfactorily by the use of compressed air. A paper filter will require replacement at periodic intervals. If the element is of metal gauze, it may be washed in paraffin. Care should be taken not to damage the felt seals at either end of the element that otherwise could require replacement.

23.8 Standard lubrication 23.8.1 Ball/roller bearings with provision for lubrication Packed with grease at assembly, these bearings need little further attention other that the occasional addition of a small amount of grease. If examination becomes necessary, clean and flush out the bearing with an environmentally safe, approved quick drying solvent and if the bearing is serviceable, re-pack with new grease.

23.8.2 Sealed ball bearings This type of bearing is lubricated for the life at the time of manufacture, and no provision is made for lubrication. If the bearing is running noisily, it should be replaced rather than refilled.

23.8.3 NSK-RHP self lube bearings These bearings are factory charged with the correct type and quantity of grease at the time of manufacture and seldom require recharging. If the bearings do however require more grease (due to excessive loads or operating temperatures for example), they can be recharged with two or three shots of grease chosen from the Recommended Lubricants chart.

23.8.4 Recommended lubricants Reference should be made to the supplier’s lubrication information.

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The required frequency of lubrication checks and changes is dependent upon the operating conditions of the equipment. The following schedule is given as a guide, which will be appropriate for most installations (Table 23.2). TABLE 23.2

General lubrication schedule.

Item

Frequency

Lubricant

Heavy duty gears

Every day

Lubricate/grease

Driving chains

Every week

Oil as required

Light duty gears

Every week

Lubricate/grease

All gearboxes

Every week

Check oil levels and replenish if necessary

Fan and motor bearings

Every 3 months

One or two shots only of the appropriate grease

All gearboxes

Every 6 months

Change the oil

Bronze oilretaining bushes

Every 6 months

Apply oil liberally, allow some to be absorbed by the bush and then clean off the surplus oil

23.8.5 Every 200 h Driving chains

Oil lightly

All gearboxes

Check the oil levels and replenish if necessary

Bearings

Check for any loss of grease

23.8.6 Every 2500 h Fan and motor bearings

One shot of the appropriate grease

Delivery end sprag clutch

Fill with the grease until it emerges past the seals

Feed and delivery end drum

One shot of the appropriate grease for bearings, oven band support roller bearings, band cleaner and shaft bearings

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23.8.7 Every 5000 h All gearboxes

Unless otherwise advised change the oil

Bronze oil-retaining bushes

Apply oil liberally. Allow some to be absorbed by the bush then clean off the surplus oil

23.8.8 Each year Fans

Strip the bearing assemblies, clean the races and housings and re-pack with recommended grease

23.9 Maintenance log or record It is essential for the user to record all maintenance activities on the equipment. The log will assist in identifying any persistent problems, keep track of consumable and spares items used and also act as a means of communication from one group of maintenance engineers to another. A sample chart for this log is shown below. Maintenance record: line No. . . .. . .. . .. . .. . .. . .. Refer Table 23.3.

TABLE 23.3

Maintenance record line no.

Details of work done

Date

Signature

23.10 Recommended spare parts It is recommended that the factory has a stock of key spare parts. Failure of key parts can cause one or more zones of the oven to be shut

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down. The following parts should be readily available to the maintenance engineers.

23.10.1 Gas system • • • •

Main gas supply manual shut-off valve Main gas supply solenoid valve High and low gas pressure switches for the gas train Spare Dungs zero gas governor for DGF oven.

23.10.2 Weishaupt burners • Dungs high and low pressures switches • Gas shut-off valve for Weishaupt burner.

23.10.3 Maxon burners • • • •

Landis and Gyr Maxon burner control unit Flame detector/flame eye for Maxon burner Combustion fan air pressure switch for Maxon burner Ignition rod for Maxon burner.

23.10.4 Flynn burners • Flynn ignition control units • Flynn spark ignition electrodes • Gas solenoid valves for Flynn burners.

23.10.5 Electrical/temperature control parts • • • • • • • •

6 min fixed purge timer Antunes pressure switches for the circulating and extraction fans Bake time/band speed proximity sensor (Synatel) Selection of thermocouples to suit all ovens Thermocouple high temperature compensating cable Omron oven temperature controller Omron over temperature display unit A range of spare electrical motor inverters.

23.10.6 Mechanical parts • Range of belts to suite all type of fans • Complete range of bearings for all drives, fans, rollers, etc.

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• Spare stripping blade at oven transfer to stripping conveyor • Spare brushes (and flapper material) for band cleaners.

References Baker Pacific. Cambridge CB24 9YZ, United Kingdom. www.bakerpaciific.net. Baker Perkins Ltd. Manor Drive, Paston Parkway, Peterborough, PE4 7AP, United Kingdom. www.bakerperkins.com.

Biscuit Baking Technology

A P P E N D I X

1 Ingredients for biscuits: an introduction

1 Flour 1.1 Wheat flour The flour shall be milled from good-quality soft wheat, free from infestation and impurities, especially pesticides. The flour shall not be treated with enzymes and shall not contain chemical additives. The appearance shall be a good white colour, free from bran particles. The odour shall be free from mustiness and foreign odours. Two flours are typically used, described in the recipes as weak and strong. An analysis of each is given below. Weak/medium flour Semi-sweet doughs

Strong flour Fermented doughs

Starch

74.5

71.5

Moisture

14.0

13.5

Proteins (gluten forming)

7.0

10.0

Proteins (soluble)

1.0

1.0

Sugar

2.0

2.5

Fat

1.0

1.0

Ash (mineral salts)

0.5

0.5

Total

100.0

100.0

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1.2 Corn flour Corn flour is a white free flowing powder produced by wet milling of maize, followed by washing, concentrating, centrifuging, drying, milling and sifting to give a natural maize starch. It has a short gel texture and relatively high viscosity and is easily dispersed in cold water.

2 Sugars and syrups 2.1 Sucrose The sugar shall be free from impurities and infestation. The appearance shall be a fine, white crystalline solid, free flowing and free from lumps. The sugar shall have a sweet taste and be free from odours. Moisture content: 0.06% maximum Ash content: 0.03% maximum Particle size • • • •

Powdered sugar: 60 µm Crystal sugar: 150 µm Caster sugar: 150 450 µm Granulated sugar: 450 600 µm

Brown sugar is a dry golden brown sugar with bold crystals. The sugar should be dry and free flowing. Particle size: 0.8 1.2 mm

2.2 Glucose syrup Glucose syrup (C6H12O6) is a solution (up to 80%) of glucose (dextrose), maltose and malto-dextrins in water. It is normally obtained by enzymatic hydrolysis of starch. Starch from wheat, corn, potato, cassava or any other plant can be used for this purpose. Standard glucose syrup has a DE value (dextrose equivalent) of 42. The relative sweetness of 42DE glucose to sucrose is 40% 45%.

2.3 Cane syrup 80% Syrups with 80% solids are derived from the refining of cane sugar and used for their excellent flavour.

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2.4 Invert syrup 70% Syrup of 70% solids is made by acid hydrolysis of sucrose. The result is a 50:50 mixture of dextrose and fructose which are both reducing sugars and contribute to the Maillard reaction in baking.

2.5 Fructose syrup 80% Commercially, fructose is usually derived from sugarcane, sugar beets and corn. Crystalline fructose is a monosaccharide, dried and ground, and of high purity. High-fructose corn syrup is a mixture of glucose and fructose. It is much sweeter than glucose.

2.6 Malt extract 80% A thick glutinous syrup of 80% solids is usually non-diastatic and obtained by water extraction of malted wheat or barley. The heat treatment used to concentrate the solution destroys any enzymes. It used as an important flavour ingredient. It is rich in maltose, which is a reducing sugar.

3 Fats 3.1 Dough fat The fat shall be free from impurities and appear clean and bright when melted. The fat should be odourless, free from rancid and foreign flavours. The fat should be produced from good-quality crude oils by a process of refining, bleaching and deodorising. It should be made primarily from vegetable oils, but it may contain hydrogenated fish oils. Free fatty acid (as oleic acid)

Maximum 0.08%

Peroxide value (mg equivalent per kg)

Maximum 1.0

Moisture

Maximum 0.1%

Slip melting point (BS 684 1.3 1976)

34 C to 37 C

3.2 Butter Butter is used for its shortening and flavour. The flavour of the butter is complemented by sugar and vanilla during baking and changes to a mild toffee or butterscotch flavour with good aroma.

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Anhydrous butter or butter oil has almost no moisture and is harder than butter.

3.3 Palm oil Bleached, filtered and de-odorised. Free from rancid or foreign smell. Melting point: 36 C 38 C

3.4 Coconut oil Hydrogenated coconut oil, neutralised, de-odorised and bleached. Often used in the oil spraying of crackers. Melting point: 32 C 34 C

4 Dairy products 4.1 Whole egg powder Whole egg powder is spray dried. Egg is an ideal medium for the growth of micro-organisms so great care must be taken to store and handle it with sterilised implements. Egg yolk is rich in fat and lecithin and it is these ingredients together with the flavour, which contribute to the biscuit recipes.

4.2 SMP, FCMP—skimmed milk powder, full cream milk powder Skimmed milk powder is the liquid remaining after the fat is separated from the milk for cream or butter. It is concentrated and dried. It is rich in lactose and proteins and is important for the Maillard reaction where it contributes to the development of the brown colouring. It also adds flavour.

5 Leavening agents 5.1 Yeast (fresh) A microscopic, unicellular organism. It breaks down sucrose and maltose into monosaccharides and glucose and fructose into alcohol and carbon dioxide. During fermentation, the yeast will cause gluten modification and flavour development.

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5.2 Ammonium bicarbonate (“Vol”) (NH4)HCO3 A volatile salt, which, when heated liberates carbon dioxide, ammonia gas and water.

5.3 Sodium bicarbonate (“Soda”) NaHCO3 The most important aerating agent. When heated it liberates carbon dioxide and water, leaving sodium carbonate as the residual salt. Sodium carbonate has a softening action on gluten and darkens the biscuit. If sodium bicarbonate is heated, only half the carbon dioxide is released, but if an acid is present, all the carbon dioxide is released and there is no softening action on the gluten or darkening of the colour of the biscuit.

5.4 ACP—acid calcium phosphate Acid calcium phosphate is also known as monocalcium phosphate. It is fairly soluble in cold water, but for doughs which are used without standing, a good proportion of the reaction takes place during baking. It is used in conjunction with sodium bicarbonate and ammonium bicarbonate.

5.5 SAPP or PURON—sodium acid pyrophosphate Sodium acid pyrophosphate is an acid salt used in the baking industry with sodium bicarbonate to enhance the leavening. It combines with sodium bicarbonate to release carbon dioxide.

6 Emulsifiers 6.1 Lecithin Emulsifiers assist the blending of the fat in the dough. Lecithin is the most commonly used emulsifier in biscuit making. It is a complex natural surfactant obtained from soya beans.

6.2 GMS—Glycerol monostearate A monoglyceride used as an emulsifier. It permits easier blending of the fats in the dough.

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7 Flavour enhancers 7.1 Salt Sodium chloride, used as a flavour enhancer and also to control the rate and extent of fermentation.

7.2 Monosodium glutamate (MSG) C5H8NO4Na A flavour enhancer commonly added to recipes with cheese or other distinct flavours.

7.3 SSL—sodium stearoyl lactylate An emulsifier which interacts with the gluten proteins to strengthen the dough.

8 Preservative 8.1 SMS—Sodium metabisulphite Na2S2O5 Sodium metabisulphite is used in foods as a preservative. For biscuits, it acts as a reducing agent for the modification of the strength of the gluten in doughs, particularly for semi-sweet doughs. It causes the gluten to become more extensible and less elastic, reducing shrinkage during baking.

9 Enzymes 9.1 Proteolytic enzymes Proteinase is the most used enzyme in biscuit making. It is a catalyst used to break the length of protein chains and to soften the gluten in doughs and improve the machining of some biscuit doughs.

Bibliography BC Cook Articulation Committee, 2021. Major fats and oils used in bakeries. ,http:// www.opentextbc.ca.. Bender, A.E., 1990. Dictionary of nutrition and food technology, Butterworths, Boston. ,http://www.elsevier.com. 2021. Benedict, M., 2021. University of Houston. How does temperature affect yeast activity? MadSci Network. ,http://www.madsci.org/posts/archives/jan2001/980908832.Gb.r. html ..

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British Sugar plc., 2021. Screened white sugars. ,http://www.britishsugar.co.uk.. Buck, J.S., Walker, C.E., 2021. Sugar and sucrose ester effects on maize and wheat starch gelatinisation patterns. Starch. ,http://[email protected].. Eyre, C. AB Enzymes launch targets improved biscuit baking. Finelis, 2021. National Institute for Health and Welfare. Wheat flour whole grain. 20032010. ,http://www.fineli.fi/fineli/en/index.. Flour Specifications, 2021. 2 Flour specification. ,http://www.link.springer.com.. Ghiasi, K., Hoseney, R.C., Varriano-Marston, E., 1981. Effects of flour components and dough ingredients on starch gelatinisation. Cereal Chem. 60 (1), 58 61. http://www. cerealsgrains.org. 2021. Lansbergen, G., 2002. Fats for food consultants. ,http://www.fatsforfoods.com/specifications.htm.. Lowe, B., 2021. Experimental cookery from the chemical and physical standpoint. Gluten. 2009. ,http://www.olinelibrary.wiley.com.. Manley, D., 2001. Biscuit, Cracker and Cookie Recipes for the Food Industry. Woodhead Publishing Ltd. Manley, D., 1998. Ingredients. Woodhead Publishing Ltd. Moodie, P., 2021. Traditional baking enzymes proteases. Enzyme Development Corporation. Presented at American Institute of Baking, Manhattan, Kansas. 2001. ,http://www.researchgate.net.. Toufeili, I.B., Shadarevian, S., Baalbaki, R., Khatar, B.S., Bell, A.E., Schofield, J.D., 1999. The role of gluten proteins in the baking of Arabic bread. J. Cereal Sci. http://www.bakeryandsnacks.com. 2021.

A P P E N D I X

2 Specification of a multi-purpose oven 1.27 3 91.9 m

1 Oven feed end • • • • • • • •

Robust frame with machined slides and pneumatic tension system. Provision to clean and lubricate slides. Oven drum 1100 mm diameter. Drum centre to baking chamber: 3.0 m (drum centres 100.0 m). Dough scraper to remove scrap from the drum, with scrap tray. Plough to remove debris from inside of oven band. Band wander warning device, with visual and audible alarms. Automatic shutdown of oven band drive and burners in the event of an excessive deviation of the band. • Compressed air supply required 5 6 bar, negligible consumption. • Air reservoir. • Provision for fitting steam application tube at oven entry.

2 Direct gas fired zone 31.9 m long with three heat control zones Direct gas fired oven section rated for cracker production. The baking chamber has a low crown height ensuring maximum radiant effect and optimum control of airflows.

387

388

Specification of a multi-purpose oven 1.27 3 91.9 m

Three temperature control zones, 8.7, 11.6 and 11.6 m long. Each zone includes: • • • • • • • • • • • • • • • •

Baking chamber of Zone 1 is constructed in stainless steel. Oven band supported on skid bars. Positions for the mounting of 88 Flynn burners. Full width extraction system. Extraction fan with damper and linear adjustment. Damper control with setting indication for operator adjustment. Damper to have minimum setting position to reduce extraction. Purge control adjustable up to 6 mins with 5 changes of the volume of air in the baking chamber (FM compliant). Baking chamber 550 3 1515 mm cross section. Insulation: 25 mm ceramic blanket and high-density mineral wool 144 kg/m3. One hinged inspection door on burner side in each zone with adjustable spotlight. 11 access doors on non-burner side for cleaning. The opening is level with the base of the oven for ease of cleaning. Explosion relief panels in oven top. Height of oven entry adjustable within 100 mm opening. Joining section for indirect radiant section with expansion take up by bellows section 0.5 m long. Covers provided to the floor. Electrical control panels in Rittall-type enclosure (Panels are mounted outside the oven to allow air circulation).

3 Direct gas fired burners and gas equipment Fuel: Natural gas. Maximum heat rating: 1634 kW (1,405,240 kcal/h)

3.1 Gas train One gas train comprising: • • • • • • • •

Manual shut off valve. Two automatic shut off valves for safety system. Gas filter. Zero-pressure gas governor. Gas pressure high/low detection. Gas pressure gauges (2) at gas inlet and outlet of gas train. Gas valve tightness proving facility. Main gas pipes and gas distribution system.

Specification of a multi-purpose oven 1.27 3 91.9 m

389

• The gas pressure is monitored during operation for high and low set points and the burners will be automatically extinguished if these set points are exceeded.

3.2 Air supply • • • • • • •

Six combustion air fans and motors Six air filters Six air pressure gauges Six motorised butterfly valves for top and bottom air pressure Six modutrol motors with linkages Braided air hoses between air pipe and each burner Low-pressure switch

3.3 Burner system • • • • • • • • • •

86 burners with 1250 mm strips, ribbon pattern 0.187 2 port. Including 12 burners with Trizone flame adjustment in 3 sections. Turndown ratio: 4/5:1. Strip design and material: stainless steel corrugated strips. 86 flame managers. Air-blast injectors for each burner. One manual gas valve per burner. One solenoid valve per burner. Flexible gas pipes, each 600 mm long. Burner support bars in Zone 1 is made of stainless steel.

3.4 Automatic temperature control • Four thermocouples are installed in each oven zone to detect the baking temperatures. These provide signals to Eurotherm 2408 controllers at the zone control panels. • The Eurotherm controllers provide temperature setting and monitoring with digital readouts. • The combustion air pressure is modulated to maintain the set baking temperatures. • The top and bottom burners in each zone are separately controlled. • Two Eurotherm 2408 controllers are provided for each zone for separate top and bottom control settings.

4 Indirect radiant oven Length of baking chamber: 60.0 m Four zones: lengths 12.0, 16.0, 16.0 and 16.0 m

390

Specification of a multi-purpose oven 1.27 3 91.9 m

Each zone is equipped with the following: • • • • • • • • • • • • • •

nine (9) tube radiator heaters above and below the oven band cyclotherm heating system with circulation fan air ventilation to cool the fan and motor control of airflow to tube radiators by sliding plate dampers to top and bottom and left and right giving four separate control sections in each baking zone adjustment plates for airflow to radiant tubes to balance lateral heat turbulence system to improve heat transfer and efficiency turbulence/extraction fan with damper controls for top/bottom control air ventilation to cool the fan and motor side screens with adjustment outside baking chamber to control the airflow at the sides of the oven band (control of edge colour) insulation: ceramic blanket 25 mm thick and high-density mineral wool mattress 144 kg/m3 16 clean out doors to be provided on the non-burner side (total number) one inspection door on burner side in each zone with spotlight covers provided to the floor level electrical panel in Rittall-type enclosure

4.1 Oven burners • Four (4) Weishaupt WG 30 N/1-C burners for natural gas, each 40- to 350-kW capacity. The burners are fully modulating • Four (4) modulating controllers and motors • Total maximum heat rating: 1400 kW (1,204,000 kcal/h) • Fuel: natural gas • Explosion relief panels opposite each burner to allow relief of pressure • Burner tubes 310 stainless steel • Weishaupt flame detectors • Burner flame managers: Siemens W-FM20

4.2 Gas train Each burner is equipped with a gas train: • • • • • •

Gas Gas Gas Gas Gas Gas

valve train with double magnetic valves (DMV) 3/4v size low pressure switch governor (gas supply pressure 7 15 pascals) filter—WF-3025/1 ball valve DN.25 PN16 leak proving test

Specification of a multi-purpose oven 1.27 3 91.9 m

391

4.3 Automatic temperature control • Four thermocouples are installed in each oven zone to detect the baking temperatures. These provide signals to Eurotherm 2408 controllers at the zone control panels. • The Eurotherm 2408 controllers provide temperature setting and monitoring with digital readouts. • The burners are automatically modulated to maintain the set baking temperatures.

4.4 Turbulence/convection system • Turbulence fan (fixed speed) to distribute convective air to ducts above and below the oven band • Turbulence ducts adjacent to return ducts to use heat from the return airflow to the burner • Even distribution of turbulence from full width ducts running the length of the zones • Adjustment to for top and bottom airflow

4.5 Thermocouples and pressure gauges • The piping is arranged to avoid condensation entering the instruments.

5 Oven band • • • •

Steinhaus F4102/K-st wire-mesh band, 1.270 m wide. Band height 1220 mm. Oven band supported on cast iron skid bars. Return band supported on rollers. The height and angle of the rollers is adjustable. Part rollers supplied with spring loaded collars to aid band tracking. • Oven band tracking to 1 / 10 mm on each end drum. • Automatic band tracking units are fitted at each end of the oven. • Band wander warning detection and alarm at each end of the oven. Alarm sounded if the band deviates 1 / 10 mm. Alarm sounded and oven drive is automatically stopped if the band deviates 10 1 10 mm to either side

392

Specification of a multi-purpose oven 1.27 3 91.9 m

5.1 Oven band cleaner • Top wire brush to clean inside of the oven band with fixed speed drive. The unit is mounted on the oven frame with lever to raise clear of the band and lower to the working position. • Bottom wire brush unit to clean the outside of the oven band with fixed speed drive and mounted on a trolley for removal to the side of the oven. Guide rails are provided for the trolley with stops and locking handle. The brush is raised to the working position by a lever.

6 Delivery end section • Drum 1100 mm diameter • 5.0 m from baking chamber to oven drum centre • Oven band drive with speed range to suit a 3.0 9.0 mins baking time (mean position 4.5 mins) • SEW drive with inverter control • Standby DC motor with sprag clutch for emergency drive • Band wander warning device. • Wire mesh stripping conveyor 2.0 m long incorporating adjustable discharge level and retractable end for reject Emergency drive: In the event of a power failure, the oven band will be automatically driven by a standby DC motor powered by a battery pack with charger. The battery pack and charger are mounted in a separate enclosure adjacent to the main panel. The battery pack will provide power to the DC motor for 30 mins.

6.1 Oven end extraction hood Stainless steel hood 2.0 m long mounted over the oven discharge end, with extraction fan.

7 Control panels Main panel located at oven delivery end with Rittall-type enclosure with controls for oven band drive, baking time and band wander warnings. Zone controls located in a Rittall-type enclosure with controls for burners, gas system, temperature setting, over temperature, circulation and turbulence fans. The control panels are mounted outside the oven to allow air circulation.

Specification of a multi-purpose oven 1.27 3 91.9 m

393

Control panels are provided at each oven and with band tension and tracking warning and fault displays and emergency stop buttons.

8 Oven safety systems 8.1 Oven band The band is monitored for excess movement using limit switches at each end of the oven. Early warning and trip positions are provided. After band wander trip, there is an override facility for re-start of the band. Maximum deviation 1 / 10 mm Deviation over 1 / 10 mm sounds alarm Deviation over 20 mm stops the oven band and shuts down burners The band tension is monitored and tension must be present before starting the oven band. The band will stop under certain conditions, for example, power failure and excessive band deviation. The band movement is monitored and if the band stops all burners will be automatically extinguished.

8.2 Ignition The burner ignition/shut down sequence is controlled by a dedicated control unit. Flame failure, gas pressure, air pressure and fan pressure are monitored by the controller.

8.3 Purge system Before lighting the burners, the system will ensure that the circulation fans operate with the flues open. The purge cycle is 6 mins duration.

8.4 Over temperature The zone temperature is monitored by a Eurotherm controller. Excess temperature, which is pre-set, will cause the gas supply to be shut off and all burners extinguished.

8.5 Power failure The gas supply will be shut off and all burners will be automatically shut down. The DC motor will start automatically to empty the oven of biscuits.

394

Specification of a multi-purpose oven 1.27 3 91.9 m

9 Components and finishes 9.1 Electrical installation Electrical supply: 380 v 3 phase 50 Hz 1 neutral Max. voltage fluctuation: 1 / 8% Control voltage: 220/24 v Supplier will supply site wiring materials, including cables, cable trunking, junction boxes and other materials for wiring from the control panels to the motors and other electrical equipment.

9.2 Components Materials and components in metric system Pneumatic equipment: Festo Electrical equipment: Telemecanique Temperature controllers: Eurotherm Frequency inverters: Telemecanique Electrical cabinets: Rittall equivalent Gearboxes: Nord Motors: Siemens Batteries and charger: Erskine Systems Ltd., United Kingdom

9.3 Finishes Direct gas fired baking chamber (Zone 1): stainless steel Direct gas fired baking chambers (Zones 2 and 3) and cyclotherm baking chambers and ducts outside: Heat-resistant aluminium paint Outer side panels: powder coated white Frames, support legs and bottom and top covers: powder coated black Panel fascias: brushed aluminium Oven end top covers stainless steel

Bibliography Baker Pacific, 2021. Cambridge CB24 9YZ, United Kingdom. www.bakerpacific.net.

A P P E N D I X

3 Oven manufacturers

1 China 1.1 Dongguang Furong Food Machinery Factory Nanshe industrial Chashan Town, Dongguan City, Guangdong Province 523391, China http://www.made-in-china.com 2021

1.2 Evergrowing Food Machinery Co. Ltd Rixin Building, No. 1 FuTian Road, NanXi Industrial Zone, Xiang Zhou, Zhuhai, Guangdong Province, China. http://www.biscuitequipment.com 2021

1.3 Shanghai Kuihong Food Machinery No. 1528, Hubin Road, Huqiao Town, Fengxian District, Shanghai http://www.kuihong-foodmachine.com 2021

1.4 Sinobake, Guandong Shunde Huaji Industrial Co Kunzhou Industrial Zone, Beijiao Town, Shunde, Foshan City, Guangdong Province, China www.sinobake.net 2021

395

396

Oven manufacturers

1.5 Skywin Foodstuff Machinery Co. Ltd Nanchong Industrial Zone, Chencun, Guangdong, China http://www.skywinbake.com 2021

Shunde,

Foshan

City,

1.6 Zhongshan Dingson Food Machinery Ltd 13 Teng Yun Road, Tanzhou Town, Zhongshan City, Guangdong Province, China. http://www.dsm-mc.com http://www.dingson.en.made-in-china.com 2021

1.7 Zhuhai Hong Fu Mechanical Manufacturing Co. Ltd Landun Rd, Xiangzhou, Zhuhai, Guangdong Province, China http://www.hfmachine.en.made-in-china.com

2 EUROPE 2.1 Aasted ApS Bygmarken 7 17, DK 3520, Farum, Denmark http://www.aasted.eu 2021

2.2 Baker Perkins Ltd Manor Drive, Paston Parkway, Peterborough, PE4 7AP, United Kingdom http://www.bakerperkins.com

2.3 Baker Perkins Inc 3223 Kraft Ave. S.E. Grand Rapids, MI, 49512 2027, United States http://www.bakerperkins.com

2.4 Bu¨hler Group (DFE Meincke, Haas, Vuurslag) Gupfenstrasse 5, Uzwil 9240, Switzerland http://www.buhlergroup.com 2021

Oven manufacturers

397

2.5 GEA IMAFORNI INT’L S.p.A Via Stra`, 158, 37030 Stra`-Montanara-Pieve VR, Italy http://www.gea.com 2021

2.6 Laser Srl Via Saturno 36, 37059 Santa Maria di Zevio, Verona, Italy http://www.laserbiscuit.it 2021

2.7 Pek Makina 27. Cd. No: 5, 26110 Osb/Odunpazarı/Eski¸sehir, Turkey http://www.pekmakina.com 2021

2.8 Polin, Ing POLIN E C. SpA Viale dell’Industria 9, 37135 Verona, Italy http://www.polin.it 2021

2.9 Senius Equipment Aps Industrivej 15, 8830 Tjele, Denmark http://www.senius.dk 2021

2.10 Spooner Vicars Bakery Systems Middleby House, Unit 15, Bridge Bank Close, Off Yew Tree Lane, Stonecross Park, Golborne, Wigan, WA3 3JD, United Kingdom http://www.spoonervicarsbakery.com 2021

2.11 TMFCT

Bonnand Lornac

Zone Industrielle, 26 rue de St Re´my, 28270 Brezolles, France http://www.tmfct.fr 2021

2.12 Werner & Pfleiderer Industrielle Backtechnik GmbH, Frankfurter Straße 17, 71732 Tamm, Germany http://www.wpib.de 2021

398

Oven manufacturers

3 India 3.1 Bake-o-Nomic Corp No. 1, M & N Estate Off Western Express Highway Mira, Mumbai, Maharashtra-401104, India [email protected]

3.2 Besto Oven Industries 9920413066 Unit No. 108, Acharya Complex, CG Road, Chembur East, Mumbai, Maharashtra-400074, India http://www.ovenindia.com

3.3 Esspee Engineers, Kolkata Diamond Heritage, 16 Strand Road, 6th Floor, Room No N, 627, Fairlie Pl, Kolkata, West Bengal-700001, India http://www.espenger.com

3.4 New Era Machines New Era Machines Private Ltd.Majara Road, Sahnewal District, Ludhiana-141120, India http://www.neweramachines.com

3.5 Ovenman Industries Private Ltd B 14 15 Industrial Area, Site 1, Haripur, Jalalabad, Lucknow Road, Faizabad-224 001, India http://www.ovenmanindia.com

4 Japan 4.1 Misuzu Koki Co Ltd 530 Kitagomizuka, Kusu-Cho, Yokkaichi, Mie 510 0103, Japan http://www.misuzukoki.jp

4.2 Naigai-Vicars Okura Honkan, 2 6 12 Ginza, Chuo-ku, Tokyo 104 0061, Japan http://www.naigai-vicars.com

Oven manufacturers

399

5 Korea 5.1 Dong Yang Food Machinery Co. Ltd 23, Dusan-ro 11-gil, Geumcheon-gu, Seoul 08525, Republic of Korea http://www.mixer.co.kr http://www.dyfm.co.kr

6 United States 6.1 Baker Perkins Inc 3223 Kraft Ave. S.E. Grand Rapids, MI, 49512 2027, United States http://www.bakerperkins.com

6.2 Reading Bakery Systems 380 Old West Penn. Avenue, Robesonia, Pennsylvania, 19551, United States http://www.readingbakery.com

A P P E N D I X

4 Oven band manufacturers

1 Agrati La Bridoire Sarl 640 Route du Lac, 73520 La Bridoire, France http://www.ovenband-labridoire.com

2 Ark Engineers Thakur Niwas 16-D, Samrath Mill Compound, LBS Marg, Vikhroli-W, Mumbai, Maharashtra 400079, India http://www.arkengineers.com

3 Ashworth Bros. Inc 450 Armour Dale, Winchester, VA 22601, United States http://www.ashworth.com

4 Audubon 850 Pennsylvania Blvd., Feasterville, PA 19053, United States http://www.meshbelt.com

401

402

Oven band manufacturers

5 Berndorf Band Gmbh Leobersdorfer Strasse 26, A-2560 Berndorf, Austria http://www.berndorf-band.at

6 Bharat Wire Mesh Company D-11, Shiv Bhole Laghu Udyog, Opp Hindustan Construction Company, Ambewadi, L.B.S. Marg, Vikroli (West), Mumbai, Maharashtra 400083, India http://www.bharatwiremesh.com

7 Cambridge Engineered Solutions 105 Goodwill Road, Cambridge, MD 21613, United States http://www.cambridge-es.com

8 Consol Machinery (Canton) Co. Ltd No. 6 Longgu Road, Shawan Town, Panyu Distr., Guangzhou, China http://www.consolsteelbelt.com

9 Durgesh Industries 113, Jawahar Colony, N.I.T., Faridabad, Haryana 121005, India http://www.wiremeshbelts.net

10 Heights Wire Belt Factory South of Development Zone, Dezhou, Shandong, China http://www.wiremeshbelt.org

11 IPCO IPCO Sweden AB2453-B Va¨stra Verken, 81181 Sandviken, Sweden http://www.ipco.com

Oven band manufacturers

403

12 Rexnord Inc 511 W Freshwater Way, Milwaukee, Wisconsin, WI 53204, United States http://www.rexnord.com

13 Shri Jai Maharani Industry Guru Govind Nagar, Raipur, Chhattisgarh 492001, India http://www.bakeovenband.com

14 Steinhaus GmbH Platanenallee 46, 45478 Mu¨lheim an der Ruhr, Germany http://www.bakingovenbelts.com

15 Yangzhou Jiangdu Huada Metal Mesh Belt Factory Baisha Road, Daqiao Town, Jiangdu District, Yangzhou, Jiangsu 225211, China http://www.meshbelt.cn

16 Yangzhou Jinrun Mesh Belt Manufacturing Co No. 2, Dachang Road, Daqiao Town, Jiangdu City, Yangzhou, Jiangsu 225211, China http://www.en.wmbbelt.com

Index Note: Page numbers followed by “f” refer to figures. Baking Ovens Conversion to electrical heating, 108 Dielectric, 125 Direct Convection Ovens, 117, 117f Direct Gas Fired Ovens, 9, 105 108, 106f, 135f, 143 151, 144f, 152f Electric ovens, 109 110, 110f Hybrid Ovens, 120 121, 121f Direct gas-fired/convection ovens, 121 Direct gas-fired/indirect radiant ovens, 120 121 Indirect Convection ovens, 118, 118f Indirect radiant ovens, 111 113, 112f Modular ovens, 133 Re-circ ovens, 119 Turbulence systems, 114 Baking Ovens: Components (Direct Gas Fired Ovens) Baking chambers, 143, 144f Chamber support slides, 146 Cleanout doors, 151, 151f Cracker breaker, 10 Dimensions, 145 Expansion joints, 146, 146f Explosion relief, 149, 149f, 150f Extraction system, 151 153, 152f, 284 Fan specification, 152 153 Halifax fans, 152f, 176f, 262f Inspection doors, 150, 150f Insulation, 98f, 147, 147f Materials, 145 Oven end hood, 153 Pressure switches, 284f, 356, 357f Return band covers, 148, 148f, 149f Baking Ovens: Components (Indirect Radiant Ovens) Baking chambers, 167 168, 168f Burner tube, 172f Circulation, extraction fans, 174 175, 175f Cleanout Doors, 178 Expansion joints, 169, 169f, 170f

Explosion relief, 177, 177f Extraction, turbulence system, 175 176, 176f Halifax fans, 175f, 176f, 262f Heater module, 170 172, 171f Heat exchanger flue, 177 Inspection doors, 178, 178f Insulation, 177 Radiant tubes, 92f, 172 174, 173f Return ducts, 174 Baking Ovens: Specifications Calculation of zone lengths, 134 139 Crackers, 123 126, 123f Crispbreads, etc, 127f Heat ratings, 135f Semi-sweet biscuits, 129, 129f Short dough biscuits, 130 132, 130f Baking Ovens: System for Heat Recovery (HRS) Calculations of hot air flow, 191 193 Control dampers, 190 Flues, 187 189 HRS system, 187 193, 187f, 319 320, 319f HRS zone, 189, 189f Baking Process Biscuit structure, 45 46 Colour, 46, 46f, 53 54 Data loggers, 361 363 Moisture content, 46, 52 Process, 45f, 54f Baking Profiles Baker Perkins direct gas-fired oven, 58f Cookies, 70 72, 70f, 73f Crackers, 57 60 Marie biscuits, 67f Ritz-type cracker, 64f Semi-sweet biscuits, 64 67, 65f Short dough biscuits, 68 69, 68f, 69f Snack crackers, 61 64, 61f Soda and saltine crackers, 57f Soda crackers, 60f

405

406

Index

Biscuit Baking, Energy for Carbon dioxide emission from burning natural gas, 336 337 Carbon footprint, 339 Climate change and greenhouse gases, 337 338 Combustion process, 335 336 Consumption of gas for baking, 338 Electricity generation from renewables, 341 342 Energy sources, 339 Energy usage for baking, 338 Future developments, 342 New biscuit bakeries, 343 Power generation costs for renewable energy, 340 341 Renewable Energy Master Plan (REMP), 341 Solar energy for a new bakery, 344 Stoichiometric combustion, 336f Biscuit Design and Output Cutter and moulding roll layouts, 75 77, 76f Docker pins, 81 82, 82f Output calculation, 84 85 Oven band loading, 83 84 Oven size and output, 84 85 Scrap and scrapless designs, 79f Semi-sweet biscuits, 79 80, 79f Short dough biscuits and cookies, 80 Soda crackers, 78f Biscuit Ovens, Manufacture of Baker Pacific direct gas-fired/indirect radiant oven, 289f Component assembly and exploded view of assembly, 295f, 296f Contractors, 297 298 Control and safety systems, 296 Direct gas-fired baking chambers, 290f Fabrication work, 297f Indirect radiant heater module, 297f Installation, 299, 300f Local manufactures, 289 291 Manufacturing drawings, 293 295 Oven foundation drawing, 293f Purchasing, 298 Shipping, 298, 299f Team and experience required, 291 292, 291f Biscuits Cakes, 38 42 Chocolate chip, 28 34, 31f

Cookies, 1 2, 28 30, 29f Crackers, 1 4, 3f Cream crackers, 11 13, 11f Cream mixer, 36f Danish butter cookies, 30f, 133 EverSmart two-colour sandwiching machine, 38f Filled cookies, 30f Ginger, 27, 27f Glucose, 24f Golden Maria/Dorada, process for, 21 23, 21f Jaffa cakes, 40, 40f Korean pies, 39f Maria, 82f Marie, 18f Process for cookies, 31 34 Process for crackers, 14 Process for laminated crackers, 11 13 Process for short dough biscuits, 23 28 “Ritz” type crackers, 14f Sandwich biscuits, 34 37, 35f Semi-sweet biscuits, 16 20, 17f Short dough biscuits, 23 28, 23f Snack cakes, 38 42, 39f Snack crackers, 13 16, 13f, 14f Soda crackers, 4 11, 4f Burners and Gas System for Direct Gas Fired Ovens, 153 162 Burner installation, 155f Combustion air, 154, 280 Control panels, 157f, 162 165, 163f, 165f Direct Gas Burners (Flynn), 157 161, 158f, 358 359 Electric trunking, 166f Gas / air mix, 282 Gas systems, 277 279 Gas train, 154, 278, 278f Infrared metal fibre burners, 161 162 Metal Fibre burners, 107f, 161f Multi-flame burners, 161f Over temperature, 279, 283 Purge system, 279 Spark monitor system (Flynn), 160f, 281 Temperature control, 155 157, 363 Temperature controllers, 157f, 363 Burners and Gas Sytem for Indirect Fired Ovens, 179f Gas systems, 278 Gas trains, 278f, 358f Gas valve trains, 182f

Index

Maxon dual fuel burners, 183 185, 183f, 361f Maxon gas and oil trains, 185 Over temperature, 279, 283 Purge system, 279 Weishaupt burners, 179 183, 179f, 282 283, 283f, 315f, 358f, 360f Weishaupt Combustion Manager, 181f Weishaupt gas train, 182f, 315f Conveyor Bands Heavy mesh, Compound Balanced weave, CB5 Band supports, 224 Band tracking, 225 226 Compound balanced, CB5, 95, 115, 115f, 126f, 224 226, 224f IPCO graphite station, 231f IPCO steel band cleaner, 232f Joining Ashworth bands, 226 SKF high temp bearings, 225f Steel bands, 95, 104, 114, 227 233, 230f Band cleaning, 231 232 Band greasing, 232f, 233 Band tracking, 233 Joining steel bands, 231 Steel band supports, 230 231 Wire mesh (incl. Z47), 126f, 211 222, 211f Auto band tracker, 218 220, 219f Band cleaning, 216 218, 217f Band tension, 274, 353 Band tracking, 219f, 274f, 276, 352 Guide rollers, 220 Joining bands, 221f Joining wire-mesh bands, 220 221 Return band supports, 215 216 Rolled wire-mesh belts, dimensions of, 222 Skid bars, 214f, 352, 352f Skid bar supports, 213 214 Support rollers, 215 Z-type bands, 212 Conveyor Design Band circuit, 235f Band safety systems, 274f Battery charger, 246f Calculation of motor power, 251 252 Calculation of oven band tension, 251 Calculation of torque for drive, 251 Delivery end, 241f Delivery end drum, 242, 252f Delivery end hood, 240 252

407

Drum scraper, 243f Electric motor power, calculation of, 251 252 Emergency drive, 244, 276 Emergency stops, 275 276 Feed end, 235 240, 236f Main drive, 243f Oven band drive, 274 275 Oven band position, 273 274 Oven band tension, calculation of, 251 Oven band tracking, 273 Oven drive, 243 244 Oven end hood design, 249 251, 250f Reject conveyor, 249f Safety systems, 274f Sprag clutch, 244 Stripping conveyor, 242f, 243 244, 247 249, 248f Tension system, 239f, 277 Terminal drum clamping element, 238 Terminal drums, 237 240, 238f, 241f, 242 Torque, calculation of, 251 Tracking system, 274, 274f Uninterruptible power supply, 245 246 Heat Transfer, 87, 103 105, 114 115 Baker Pacific direct gas-fired/indirect radiant oven, 104f Baker Perkins cracker oven, 97f Conduction, 95 98, 95f, 100, 101f, 104, 114 115 Convection, 98 101, 98f, 101f, 105, 107, 116 120 Cookie dough deposited on a steel band, 96f Crackers baked on an Ashworth band, 96f Direct gas-fired burners, 91f Oven insulation, 97 98 Radiation, 87 94, 88f, 99 100, 101f, 104 113 Distance, 90 Effect of radiation on the dough pieces, 90 91 Microwave, 94 Near-infrared baking, 94 Radiant heat transfer, 89 Radio-frequency (RF) baking, 92 93 Wavelength, 87 89 Ingredients, 47 50, 379 386 Corn flour, 380 Fats and oils, 50, 381 382 Gluten, 48

408 Ingredients (Continued) Leavening agents, 49 50, 382 383 Lecithin, 383 Malt extract, 381 Proteolytic enzyme, 384 Starch, 48 49 Sugar, 49, 380 381 Syrups, 380 381 Wheat flour, 47, 379 Yeast, 382 Maintenance, Oven Inspection and Audit Baking chamber, 355 357, 355f Baking temperature and humidity, 362 363 Burners (DGF), 359f Burners (Indirect), 360f Control panels, 363 Energy usage, 349 351 Extraction system, 356 Fans, 356 Gas and oil trains, 358, 358f Gas burners, 358 360 Direct gas-fired ovens, 358 359 Indirect-fired ovens, 360 Heat flux, 361 362 Oven band, 351 354 Oven band cleaner, 352f Oven band drive, 354 Oven band supports, 352 Oven band tension, 353 Oven band tracking, 353f Oven drive end, 354f Oven inspection and audit, 347 364 Oven performance, 347 351 Pressure switch, 357f Product specification, 348 Reporting, 363 364 Roller band support, 353f Safety Instructions, 284 285 Temperature control, 363 Tracking system, 353f Multi-Purpose Oven, Specification of Components and finishes, 394 Components, 394 Electrical installation, 394 Finishes, 394 Control panels, 392 393 Delivery end section, 392 Direct gas fired burners and gas equipment, 388 389 Air supply, 389 Automatic temperature control, 389

Index

Burner system, 389 Gas train, 388 389 Direct gas fired zone, 387 388 Indirect radiant oven, 389 391 Automatic temperature control, 391 Gas train, 390 Oven burners, 390 Thermocouples and pressure gauges, 391 Turbulence/convection system, 391 Oven band, 391 392 Oven band cleaner, 392 Oven feed end, 387 Oven safety systems, 393 Ignition, 393 Oven band, 393 Over temperature, 393 Power failure, 393 Purge system, 393 Oven Bands and Conveyor Manufacturers Agrati Group, La Bridoire Sarl, 401 Ark Engineers, 401 Ashworth Bros Inc, 401 Audubon, 401 Berndorf Band Co., 401 402 Bharat Wire Mesh, 402 Cambridge Engineered Solutions, 402 Durgesh Industries, 402 Heights Wire Belt, 402 List of oven band manufacturers, 401 404 Steinhaus GmbH, 403 Yangzhou Jiangdu Huada, 403 Yangzhou Jinrun Mesh Belt Manufacturing, 403 Oven Construction: Convection Ovens Baker Perkins oven module, 196f Baker Perkins TruBake HiCirc Convection oven, 196f Baking chamber, 195 199 Circulation fan, 198 199 Convection plenums, 197 Direct and indirect convection systems, 195 Heater module, 199 Maxon burner, 199f Oven Construction: Electric Ovens Baker Pacific DGF oven, 205 Control systems, 207 209 Convection ovens, 207, 207f Electrical elements, 202 204 Electric oven construction, 201, 201f, 202f

Index

Indirect radiant oven, 206 Oven efficiency, 205 Ovens with hot air circulation, 205 207 Watlow duct air heater, 206f Watlow F4T data logger, 208f Watlow SpecView SCADA Software, 208f Oven Efficiency Comparison of oven efficiencies, 329 Efficiency: table of energy usage, 328 329 Energy to bake crackers, 332 333 Energy to bake rotary moulded biscuits, 324f, 330 332 Energy to bake semi-sweet biscuits, 332 Energy to bake the product, 324f, 330 333 Energy usage, 323 329, 324f, 329f, 349 351 Heat loss, 327 328 Oven Maintenance Baker Pacific hybrid oven, 365f Electrical maintenance, 369 372 Battery safety, 371 372 Cleaning, 369 Clutches and brakes, 371 Connections and leads, 370 Earth leakage protection devices, 371 Fuses, 370 Inspection schedule for relays, 370 Limit switches, 371 Plug-in timers, 371 Proximity detectors (inductive or capacitive), 371 Relays, 370 Temperature controllers, 370 Transistor/solid-state devices, 371 Every 12 months, 373 Maintenance log or record, 376 Maintenance schedule, 372 373 Each day, 372 Each week, 372 373 Every 12 months, 373 Mechanical components, 366 369 Air lines and fittings, 367 Band pressure switch, 368 Bearings, 367 Bearings for oven band support rollers, 368 Conveyor belts, 367 Driving chains and belts, 366 Explosion panels, 368 369 Fans, 369

409

Motors and drives, 366 Oven band tension, 367 Oven band tracking, 368 Oven flues, 369 Pneumatic tension arrangement, 368 Pulleys for fans, 369 Seal and gaskets, 367 Steam lines and fittings, 366 Welded components, 366 New equipment, 365 366 Oven cleaning, 373 374 Preparation, 365 Recommended spare parts, 376 378 Electrical/temperature control parts, 377 Flynn burners, 377 Gas system, 377 Maxon burners, 377 Mechanical parts, 377 378 Weishaupt burners, 377 Routine maintenance, 366 Standard lubrication, 374 376 Oven Operation Direct Gas Fired Ovens, 303 306 Control panels, 305f, 306 307 Lighting the burners, 307 308 Safety Instructions, 284 285 Shutting down the oven, 308 Starting the oven, 303 306 Start of production, 308 Flynn ignition control unit, 307f Indirect Radiant Ovens Damper controls, 284, 316f Heat Recovery control, 319f Lighting the burners, 314 Main panels, 312f Safety Instructions, 284 285 Shutting down the oven, 318 Starting the oven, 312 317 Zone panel, 305f, 313f Process Control and Instrumentation Baking time, 260 Baking time indicator, 260f Colour control, 262 266 Colour measurement, 266 Convection ovens, 253 Direct gas fired ovens, 253, 263 Distributor ducts for lateral control, 263 Electric ovens, 253 254 Extraction ducts, 260 Extraction fans, 262f Flame Manager, 159f

410 Process Control and Instrumentation (Continued) HMI Panel View, 270 271 Humidity, 260 262 Indirect radiant ovens, 253, 264 265 Kollmorgen servo motor, 268f Multi-lane distributor burner, 159f, 263f PID control, 257 PID tuning, 258f PLC control, 266 271 Spectrophotometer, 266 Temperature controllers, 255 256, 256f Temperature monitoring and control, 254 255 Thermocouples, 254 Top and bottom temperate control (DGF), 258 260, 279 282 Vaisala Indigo 500 transmitter, 270f Zone control panel (DGF), 256f Process Control Equipment A.J. Antunes & Co., pressure switches, 284f, 357f Allen Bradley, 267 Bell Flow Systems, gas meter, 350f Brecknell Scales: ESA Precision Scales, 348f Flynn distributor burner, 263f Flynn flame manager, 159f, 160f, 280 Flynn Ignition Control Unit, 280, 280f Halifax Fans, 152 153, 175f, 176f, 262f, 356 Konica Minolta, spectrophotometer, 266f Konica Minolta CM-5 colour spectrophotometer, 349f PAX Lite Process Time indicator, 260f Red Lion Controls, 260f Sartorius moisture analyser, 349f Temperature controllers, 257f Production Machine Manufacturers Forming Machine manufacturers Baker Perkins, UK, 16f

Index

Cutter rolls, 79f ErreBi Technology, 83f Moulding roll, 76f Mixing machine manufacturers Baker Perkins, UK, 15f Dingson Food Machinery Ltd., 6f, 7f Oven bands and conveyor manufacturers Agrati Group, La Bridoire S.A.R.L., 212 Ashworth Bros Inc, 213f, 220f, 223f, 225 226 Cambridge Engineered Solutions, 224f Cross and Morse, 238f Erskine (Dale Power Solutions), 247f Euchner, 218f Martonair, 239f Rexnord Cambridge Engineered Solutions, 224f Rexroth Bosch, 239f Steinhaus GmbH, 127f, 212, 217f, 222f Synatel, 238f, 239f, 275f Oven burners and gas equipment Era-tec, 155f, 161f Flynn Burner Corp., 157 161, 159f, 160f, 263f, 307f, 359f Maxon Corp., 183 185, 183f, 361f Weishaupt GmbH, 179f, 282 283, 314f, 358f, 360f Oven manufacturers Baker Pacific, HK, 105f, 106f, 112f, 131f, 143, 153f, 187f, 215 216, 216f, 236f, 241f, 250f, 311f, 319f, 325f Baker Perkins, UK, 116f, 120f Dingson (DSM), China, 121f, 130f Oven manufacturers: list, 395 400 China, 395 396 Europe, 396 397 India, 398 Japan, 398 Korea, 399 USA, 399