Drying and Roasting of Cocoa and Coffee [1 ed.] 9781138080973, 9781315113104, 9781351624022, 9781351624015, 9781351624039

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Drying and Roasting of Cocoa and Coffee [1 ed.]
 9781138080973, 9781315113104, 9781351624022, 9781351624015, 9781351624039

Table of contents :

1. Overview of Cocoa and the Coffee Industry. 2. Drying Principles and Practices of Cocoa Beans. 3. Roasting Equipment for Cocoa Processing. 4. Flavor Development during Cocoa Roasting. 5. The Grading and Quality of Cocoa Beans. 6. Processing and Drying of Coffee. 7. Flavor Development during Postharvest and Treatment of Coffee - A Holistic Approach. 8. Roasting Equipment for Coffee Processing. 9. Flavor Development during Roasting. 10. Quality of the Final Product and Classification of Green Coffee.

Citation preview

Drying and Roasting of Cocoa and Coffee

Advances in Drying Science and Technology Series Editor

Arun S. Mujumdar

McGill University, Quebec, Canada Handbook of Industrial Drying, Fourth Edition Arun S. Mujumdar Advances in Heat Pump-Assisted Drying Technology Vasile Minea Computational Fluid Dynamics Simulation of Spray Dryers: An Engineer’s Guide Meng Wai Woo Handbook of Drying of Vegetables and Vegetable Products Min Zhang, Bhesh Bhandari, and Zhongxiang Fang Intermittent and Nonstationary Drying Technologies: Principles and Applications Azharul Karim and Chung-Lim Law Thermal and Nonthermal Encapsulation Methods Magdalini Krokida Industrial Heat Pump-Assisted Wood Drying Vasile Minea Intelligent Control in Drying Alex Martynenko and Andreas Bück Drying of Biomass, Biosolids, and Coal: For Efficient Energy Supply and Environmental Benefits Shusheng Pang, Sankar Bhattacharya, Junjie Yan Drying and Roasting of Cocoa and Coffee Ching Lik Hii and Flávio Meira Borém For more information about this series, please visit: www.crcpress.com

Drying and Roasting of Cocoa and Coffee

Edited by

Ching Lik Hii and Flávio Meira Borém

CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2020 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed on acid-free paper International Standard Book Number-13: 978-1-138-08097-3 (Hardback) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright.com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe.

Library of Congress Cataloging-in-Publication Data Names: Hii, Ching Lik, editor. | Borem, Flavio Meira, editor. Title: Drying and roasting of cocoa and coffee / [edited by] Ching Lik Hii, Flávio Meira Borém. Description: Boca Raton, Florida : CRC Press, [2020] | Series: Advances in drying science and technology | Includes bibliographical references and index. Identifiers: LCCN 2019009160 | ISBN 9781138080973 (hardback : alk. paper) Subjects: LCSH: Cocoa processing. | Cocoa trade. | Coffee--Processing. | Coffee industry. Classification: LCC TP640 .D79 2020 | DDC 338.1/7374--dc23 LC record available at https://lccn.loc.gov/2019009160 Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com

Contents P r e fa c e vii A u t h o r s ix

C o n t r i b u t o r s xi C h a p t e r 1 A n O v e r v i e w o f C o c o a a n d t h e C o f f e e I n d u s t r y 1 C H I N G L I K H I I A N D F L ÁV I O M E I R A B O R É M

C h a p t e r 2 D r y i n g P r i n c i p l e s a n d P r a c t i c e s o f C o c o a B e a n s 21 C H I N G L I K H I I , A B H AY S . M E N O N A N D C H O O N L A I C H I A N G

C h a p t e r 3 R o a s t i n g E q u i p m e n t

for

C o c o a P r o c e s s i n g 47

M I S N AW I , N O O R A R I E FA N D I E F E BR I A N T O A N D A R IZ A BU DI T U N J U NG SA R I

C h a p t e r 4 F l av o r D e v e l o p m e n t d u r i n g C o c o a R o a s t i n g 63 SUZA NNA H SH A R IF

C h a p t e r 5 Th e G r a d i n g a n d Q ua l i t y o f D r i e d C o c o a B e a n s 89 DA R I N A S H R A M S U K H A

v

vi

C o n t en t s

C h a p t e r 6 P r o c e s s i n g

and

D ryi n g

of

C o f f e e 141

F L ÁV I O M E I R A B O R É M A N D E D N I LT O N TAVA R E S DE A N D R A DE

C h a p t e r 7 F l av o r D e v e l o p m e n t d u r i n g P o s t h a r v e s t Tr e at m e n t o f C o f f e e – A H o l i s t i c A pp r o a c h 171 GE R H A R D B Y T O F

C h a p t e r 8 R o a s t i n g E q u i p m e n t f o r C o f f e e P r o c e s s i n g 235 VA N Ú S I A M A R I A C A R N E I RO N O G U E I R A A N D T H O M A S KO Z I O ROW S K I

C h a p t e r 9 F l av o r D e v e l o p m e n t

during

R o a s t i n g 267

A D R I A N A FA R A H

C h a p t e r 10 Q ua l i t y o f t h e F i n a l P r o d u c t a n d C l a s s i f i c at i o n o f G r e e n C o f f e e 311 M A R I O RO BE R T O F E R N A N D E Z A L D U E N DA

Inde x

3 43

Preface This is the first practical book dedicated to the fundamental and application aspects of two major units of operations in cocoa and coffee processing, namely drying and roasting. Drying and Roasting of Cocoa and Coffee covers key topic areas ranging from postharvest processing, equipment selection, physical and chemical changes during processing, flavor development, grading and dried product quality. Specific features of this book are as follows: • Comprehensive review on flavor development during cocoa/ coffee processing • Impact of processing parameters on cocoa/coffee quality • New trends on drying/roasting techniques and novel technology • Examines the concept of coffee quality in light of both paradigms: the traditional coffee and the specialty coffee grading systems Cocoa is the major ingredient used in chocolate making, and chocolate confectioneries are enjoyed and consumed worldwide especially during festive seasons. Processing steps, such as drying and roasting play critical roles in governing the development of its unique chocolatey flavor and aroma to produce the right quality for general consumers and chocolate artisans. Emerging markets such as Russia, vii

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P refac e

India and China are seeing an increase in demand for chocolate, and it is important to ensure good flavor consistency for global long-term market growth. Coffee is a worldwide beverage consumed by people of different cultures, and has played an important role in the history of humanity since its discovery. The consumption of coffee is usually associated with the pleasure it causes to our senses. Drinking three cups of coffee a day is associated with various health benefits. However, the sensory quality and health benefits of coffee are a phenomenon of high complexity. Several factors affect the sensory quality and final chemical compositions. Therefore, knowledge and control of the postharvest and roasting processes are crucial in the development of coffee flavor and aroma. This book gathers internationally recognized experts, who provide the latest developments in cocoa and coffee processing technologies, including updates from recent research works. No prior knowledge of cocoa and coffee processing is required, and this book is written for a variety of readers. Primarily, it is suitable for undergraduate and postgraduate students, as well as researchers and industrial practitioners/ consultants from various domains in the food and beverage industries. Ching Lik Hii Flávio Meira Borém

Authors

Ching Lik Hii is an associate professor of chemical engineering and director of the Food and Pharmaceutical Engineering Research Group at the University of Nottingham, Malaysia Campus. Previously, he was a senior research officer at the Cocoa Downstream Research Center, Malaysian Cocoa Board. Dr Hii’s key research areas include cocoa processing, drying technology and mathematical modeling. He is an editorial board member of the Malaysian Cocoa Journal and the American Journal of Food Science and Technology. Flávio Meira Borém is a full professor at the Federal University of Lavras, Brazil (Universidade Federal de Lavras). His areas of specialization are coffee processing, drying, storage and quality. Professor Borém is fully devoted to specialty coffee research. In addition to a long list of scientific publications and being an editor of two books about coffee processing, he is also an executive editor of the Coffee Science Journal.

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Contributors Ednilton Tavares de Andrade Laboratory of Processing of Agricultural Products Department of Engineering Federal University of Lavras Lavras, Brazil Flávio Meira Borém Laboratory of Processing of Agricultural Products Department of Engineering Federal University of Lavras Lavras, Brazil Gerhard Bytof Coffee Technology, Science and Research Tchibo GmbH Hamburg, Germany

Vanúsia Maria Carneiro Nogueira Brazil Specialty Coffee Association Varginha, Brazil Choon Lai Chiang Food and Pharmaceutical Engineering Group Faculty of Engineering University of Nottingham, Malaysia Campus Selangor, Malaysia Adriana Farah Food Chemistry and Bioactivity Laboratory Institute of Nutrition Federal University of Rio de Janeiro Rio de Janeiro, Brazil xi

x ii

C o n t ribu t o rs

Noor Ariefandie Febrianto Indonesian Coffee and Cocoa Research Institute Jawa Timur, Indonesia Mario Roberto Fernandez Alduenda Coffee Quality Institute Aliso Viejo, California Ching Lik Hii Food and Pharmaceutical Engineering Group Faculty of Engineering University of Nottingham, Malaysia Campus Selangor, Malaysia Thomas Koziorowski PROBAT-WERKE Werke von Gimborn Maschinenfabrik GmbH Rhein, Germany

Abhay S. Menon Centre for Sustainable Energy in Food Chains Brunel University London Uxbridge, England Misnawi Indonesian Coffee and Cocoa Research Institute Jawa Timur, Indonesia Ariza Budi Tunjung Sari Indonesian Coffee and Cocoa Research Institute Jawa Timur, Indonesia Suzannah Sharif Malaysian Cocoa Board Cocoa Innovation and Technology Center Negeri Sembilan, Malaysia Darin A. Sukha Cocoa Research Centre University of the West Indies St. Augustine, Trinidad and Tobago

1 A n O v erv ie w of C ocoa and the C o ffee I ndustry CHING LIK HII A ND F L ÁV I O M E I R A B O R É M Contents

1.1 History 1 1.2 Botany 2 1.2.1 Cocoa 2 1.2.2 Coffee 4 1.3 Processing 6 1.3.1 Cocoa Processing 6 1.3.2 Coffee Processing 8 1.4 Production 10 1.5 Consumption 12 1.6 Quality 13 1.7 Health Benefits 15 1.8 Concluding Remarks 16 References 16 1.1 History

Cocoa and coffee have been harvested for centuries for their unique characteristics, especially their taste and aroma upon processing. Both materials have been used as ingredients in many food products such as chocolates, confectioneries, sweets, pastries, beverages, dairy products and can even be used in non-food products. Commercial products made from these materials are available all year round and can be purchased anywhere from grocery shops to high street stores. Traditionally, chocolates and coffee beverages are the two most consumed products that are derived from cocoa and coffee, respectively. It has been reported that the Maya people were probably the first to cultivate cocoa in 400 AD and the origin of today’s cocoa plant can be 1

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traced as far back as 35,000 years ago (Verna, 2013). In the sixteenth century, when Hernán Cortés (a famous Spanish explorer) discovered Mexico City, he found that the Aztecs prepared a special drink known as “Chocolatl” by mixing roasted cocoa beans with maize meal, vanilla and chili (Wood, 1985). Cocoa beans were consumed not only as food but also used as currency by the Maya and Aztecs people. However, according to a famous legend, the discovery of coffee in Ethiopia was quite accidental when a goat herder noticed that his goats became more energetic after consuming coffee berries. The coffee bean was also used by Arab traders in 1000 AD in the preparation of a drink that was known as “Qahwa,” which translates as “that which prevents sleep” (BCA, 2017). Historically, coffee was introduced much earlier to Europe, in the fifteenth century, as compared to cocoa which was only introduced later in the sixteenth century. Cocoa was initially consumed purely as a drink by mixing ground-roasted beans with sugar and seasoning with spices. It was not until 1847, that the first solid chocolate bar was successfully produced by the Fry family in Britain (Verna, 2013). On the other hand, coffee is still consumed mainly as drink even today, and it has been documented that the world’s first coffee shop (Kiva Han) was opened in Turkey in 1475, with later coffee houses opening around Europe such as in Italy (1645), England (1651), France (1672) and Austria (1683). It was not until 1901, that instant coffee was invented by a chemist named Satori Kato from Chicago, Illinois (BCA, 2017). At the beginning of the twentieth century, products made from cocoa and coffee were popular, and there was a growing demand especially from the middle-class consumers. To date, cocoa continues to serve as a major ingredient in chocolate making, but its usage can also be found in several non-food applications such as pharmaceutical, cosmetic and toiletries products. The coffee drinking culture is now embedded in every level of society with almost two billion cups consumed daily worldwide (BCA, 2017). 1.2 Botany 1.2.1 Cocoa

Cocoa (family Malvaceae, genus Theobroma) is indigenous to South America and grows mostly in tropical regions that are 20 degrees north

C o c oa a n d t he C o f f ee In d us t ry

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and south of the equator. Annual rainfall of at least 1000 mm but not more than 3000 mm is conducive for cocoa planting with a temperature variation of around 18–32°C. Countries such as Côte d’Ivoire, Ghana, Brazil, Ecuador, Indonesia, Malaysia and Papua New Guinea are examples of countries that produce cocoa beans (Awua, 2002). Theobroma cacao (Figure 1.1) is the most widely cultivated species as compared to other lesser known species such as Theobroma bicolor and Theobroma grandiflorum (Toxopeus, 1985). The scientific name Theobroma cacao was given by Carl Linnaeus, a Swedish botanist, in his book Species Plantarum in 1753. In Latin, Theobroma means “Food of the Gods” and cacao is derived from the Nahuatl (Aztec) word “xocolatl.” The main varieties of T. cacao that are planted on commercial farms are Forastero, Criollo and Trinitario (Hancock and Fowler, 1994). The Trinitario variety is a hybrid of the Forastero and Criollo trees. In the current cocoa market, most of the beans traded are from Forastero trees and are commonly known as “bulk” cocoa while the Criollo beans are known as the “fine” or “flavor” cocoa which is associated with its unique flavor. Prior to ripening, the color of the cocoa fruits can range from green to red or purple; eventually turning to yellow or orange as they ripen. A ripe cocoa

Figure 1.1  Cocoa tree.

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Table 1.1  Characteristics of Forastero, Criollo and Trinitario Cocoa Beans FORASTERO Type Color of fresh cotyledons Flavor

Bulk Purple

Fruit color

Green/yellow color

Strong

CRIOLLO Fine/flavor Very light purple or white Mild and nutty Red, yellow/orange color

TRINITARIO Mainly fine/flavor Various ranges Richer than Forastero, fruity to floral profiles Various range

fruit contains beans that are covered with sweet, white mucilaginous pulps. Typically, each cocoa fruit contains about 30–50 fresh beans, but the Criollo fruit usually contains a lesser number of beans ( 10 ha)

Smallholder (farm size < 10 ha)

Natural drying • Wooden platform • Cement floor

Solar drying • Direct solar dryer • Indirect solar dryer

Artificial drying (natural convection)

Artificial drying (forced convection)

• Samoan dryer

Without mechanical mixing • Flatbed dryer

Solar drying • Hybrid solar dryer With mechanical mixing • Circular dryer • Rotary dryer

Figure 2.7  General guidelines on the selection of cocoa dryers.

of technical requirements and hence can be constructed using locally available materials (e.g., bamboo, wood and metal bars) and operated easily by the farmers. Besides, it is also low in operating cost since it utilizes only sunlight and wind which are abundant and renewable. However, major drawbacks of this method are factors related to weather conditions that can significantly influence drying time and product quality. Prolonged drying is detrimental to cocoa quality due to over-fermentation which produces a putrid off-flavor and mold formation. Other major drawbacks are product spoilage due to insect infestation as well as contamination by foreign debris and materials. Furthermore, sun drying is labor intensive as the beans need to be monitored and regularly turned for effective drying (Hii et al., 2009). Sun drying on a raised wooden platform is the most common method used by the farmers. The wooden platform can be constructed easily by using plywood, wooden planks or bamboo mats. The beans are typically loaded not exceeding one to two layers and regular turning or racking is desirable to ensure uniform drying. The platform is usually raised to a waist-level height (about 3 feet) for ease of operation. Typically, there is no restriction on the surface area requirement for drying and it solely depends on the bean quantity, land area and manpower that are available. At night, the beans are covered with a canvas sheet or moved to a covered area to prevent re-wetting by dew drops. Another method which is a slightly enhanced version of sun drying is by spreading the cocoa beans on cement floor surfaces (Figure 2.8).

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Figure 2.8  Sun drying of cocoa beans on cement floors.

Similarly, the beans are spread thinly on the floor and constant turning and racking are required. A movable roof can be installed on top of the floor surface for protection against rain and dew at night. However, a major drawback of this method is the risk of overheating the beans due to the hot cement surface which could cause a hot spot on the beans’ testa, and also regular maintenance is needed to repair the eroded cement floor. 2.3.2.2  Artificial Drying  On the contrary, artificial drying involves the direct or indirect contact of cocoa beans with a heat source for moisture removal. However, it is not recommended drying cocoa beans using direct heat (e.g., by contacting the beans with flue gases) as this could contaminate the beans and result in beans with a smoky off-flavor which is not desired (Misnawi et al., 2004). Such contamination is impossible to remove even in subsequent downstream processing and chocolate manufacturing. In general, artificial dryers that use convective hot air can be further categorized into a natural and forced convection system. The Samoan dryer (Figure 2.9) is a type of natural convection dryer which consists of a drying chamber where the fermented beans are loaded (at about 8–12 inches thick) into the drying chamber constructed of concrete and fitted with perforated aluminum platforms and below which is an indirect contact heating tube that also acts as

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Figure 2.9  Samoan dryer.

a furnace. The heating tube can be constructed using used oil drums or rolled steel plates. Hot air is generated by burning firewood inside the heating tube, and the air around the tube wall is then heated. The different densities between the heated air and the surrounding air induces a natural convective air movement passing through the beans that facilitates drying. The flue gases exit through a chimney that is constructed at the rear of the tube. However, the Samoan dryer is not very efficient due to a problem with uneven heating and the possible contamination of the beans with the flue gases from the chimney or leakages through crevices in the tube wall. In a forced convection system, the heated air generated from a furnace is forced through the beans by a mechanical blower to facilitate drying. Depending on the construction of the dryer, it can be classified as a flatbed, circular or rotary dryer. A natural convection Samoan dryer can be modified by fitting mechanical blowers on the front wall of the drying chamber. This modification helps to improve the distribution of the heated air and provide a more uniform drying.

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In a typical forced convection flatbed dryer, a wood-fired furnace is usually used to generate the heated air. Fresh air is drawn from the surroundings and heated indirectly by the heated wall surfaces that come into contact with the air. The air is then blown into the drying chamber where the beans are placed on perforated aluminum platforms. This design eliminates the need for installation of a heating tube inside the drying chamber, and hence the height of the drying chamber can be reduced by 1–2 feet. The flatbed dryer has a limitation in that bean mixing needs to be done manually. Although a mechanical bean mixer can be installed, mixing is not efficient especially for beans next to the wall and edges of the dryer (Hii and Norhaslita, 2006). In order to facilitate mixing in a forced convective dryer, circular and rotary dryers are mainly used. In the design of a circular dryer (Figure 2.10), the drying chamber is constructed in a circular shape with a diameter ranging from 6 to 10 m. A mixing arm fitted with paddle-type agitators are constructed which rotate around the center axis of the dryer. However, a problem with this design is the occurrence of bean breakage especially toward the end of drying. The design is different in a rotary dryer, where the drying chamber is constructed using two concentric, perforated horizontal steel cylinders and the inner cylinder distributes hot air through the beans that are loaded into the annulus between the cylinders. The tumbling motion of the beans and the baffles fitted to the inner wall of the bigger cylinder provides the necessary mixing action (Hii et al., 2002).

Figure 2.10  Circular dryer filled with beans, Trinidad. (Photo credit D. Sukha.)

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Rotary dryers are rarely used in the industry due to a great reduction in bean volume that leads to the excessive wastage of heated air into the surroundings. However, the final dried beans have a better appearance due to the polishing effects of the continuous brushing against each other of the beans during mixing. 2.3.2.3  Drying Efficiency  The efficiency of an artificial dryer can be

determined by using a factor known as “overall thermal efficiency (Z)” (Equation 2.6). It is defined as the proportion of energy liberated at the combustion stage that is actually used for the evaporation of moisture with the remaining proportion representing lost heat (McDonald et al., 1981). Table 2.3 shows a comparison of efficiencies among the drying methods. Typically, a forced convective dryer has better efficiency than a natural convective dryer due to its better heat distribution and combustion efficiency in the furnace. Z=



WL (2.6) FC

where W is the weight of water removed (kg), L is latent heat of evaporation of water (J/kg), F is the quantity of fuel used (kg) and C is the net calorific value of the fuel (J/kg). 2.3.3 Solar Drying

Generally, the solar dryers developed for cocoa drying can be classified into direct, indirect and hybrid type systems. The definition of a direct solar dryer is straightforward: the product inside the solar chamber (usually a transparent enclosure) is exposed directly under the sunlight. In the case of an indirect solar dryer, drying is achieved either by natural or forced convection. The product is placed in an Table 2.3  Overall Thermal Efficiency (Z) of Artificial Dryers DRYER TYPE Natural Flatbed Circular Rotary

LOADING (KG/M2)

TEMP (°C)

DRYING TIME (HR)

23.8–37.5 29.6–49.5 137–195.2 N/A

59–80 63–80 N/A 60

20–70 14–43 N/A 31.5–66

Z (%) 9–26.6 18.5–29.9 19–30 5.5–14.6

Source: Adapted from McDonald, C. R., Lass, R. A., and Lopez, A. S. F. 1981. “Cocoa drying – A review,” Cocoa Grower’s Bulletin 31, 5–41.

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enclosed chamber (non-transparent), and solar energy is absorbed by a collector which is attached to the solar chamber. The hybrid solar dryer combines both characteristics of the direct and indirect types and includes solar dryers that use another heat source in conjunction with solar energy (Fuller, 1993). Direct solar dryers are usually constructed in cabinet form where a transparent enclosure is fitted above the platform that holds the product. Minka (1986) investigated the effects of using different types of drying surface, and observations showed that a corrugated drying surface resulted in a slower drying rate compared to the bamboo mat and wire screen surfaces. Bonarparte et  al. (1998) developed and tested direct and indirect solar dryers. The direct solar dryer was constructed with a solar chamber covered with a fiberglass glazed roof. The indirect solar dryer was constructed with a non-transparent solar chamber comprising of two product shelves. A flat plate solar collector was attached to the bottom part of the dryer and a wind-assisted ventilated fan was fitted at the top of the chamber. Studies were conducted using both dryers with a loading of 13.5 and 40.4 kg/m2 of cocoa beans and a temperature increment of 20 and 15°C above ambient was recorded in the direct and indirect dryers, respectively. However, there was no significant difference in product quality between beans dried using solar and sun dryers. Hii et  al. (2006) reported similar findings as quality changes occurred at a rather similar rate during both sun and solar drying processes. Koua et al. (2017) reported that it decreased in real density (from 825.10 to 695.25 kg/m3) and increased in porosity (from 15.82 to 24.67%) with a decrease in moisture content for cocoa beans dried using an indirect solar dryer. In an attempt to improve drying efficiency, Dina et al. (2015) integrated desiccant thermal storage into the indirect solar dryer and observed decreases in drying times of up to 45.5%. A greenhouse effect (GHE) solar dryer was developed and tested in Indonesia for cocoa drying (Kamaruddin et al., 2001). The roof and wall were made of transparent fiberglass and UV-stabilized plastic sheets. Blackened steel plates were installed within the structure at both sides near the wall to enhance absorption of solar radiation. The concrete floor was also blackened (area = 3.27 m 2) and the height of the structure was 2.73 m. Two 80 watt blowers were used to ensure the uniform distribution of the hot air. An auxiliary heating unit was

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also installed to back up drying during bad weather and at night. Investigations showed a better drying efficiency, as high as 55%, in the GHE solar dryer as compared to only 10–20% in conventional drying. A significant reduction in drying time was observed in the range of 60–76%. 2.4 Product Quality

The quality of dried cocoa beans is crucial to the cocoa grinders and chocolate manufacturers as this parameter has a great impact on the final quality of the semi-finished and finished products. Conventionally, the quality of the cocoa beans is assessed for bean count, cut test, pH and flavor. Product quality such as acidity has been studied tremendously in the past by many researchers (Duncan et  al., 1989; Holm and Aston, 1993; Jinap et  al., 1994; Jinap and Zeslinda, 1995; Hashim et al., 1999). High acidity is known to mask the cocoa flavor, and it is associated with a fast drying rate under high temperatures due to the greater retention of volatile acids in dried beans. Acetic acid is the predominant volatile acid constituting 95–98% of the total volatile acids. The loss of acetic acid by evaporation is greater during sun drying as compared to high-temperature artificial drying. Therefore, sundried cocoa beans are known to have a higher pH value (less acidic) as compared to artificially dried beans. Acidity in sun-dried beans are typically registered at pH = 5 or above. The cut test is a quality control tool used in commercial cocoa grading by both buyers and sellers in the international cocoa market (Malaysian Cocoa Board, 2017). The procedure is performed by cutting the dried bean in half and examining the exposed surface of the bisected bean for color attributes such as slaty (gray), purple, partly purple/brown, brown and black. These color terminologies refer to the various degrees of fermentation, such as no fermentation (slaty), insufficient fermentation (purple), moderate level of fermentation (partly purple/brown), sufficient fermentation (brown) and over-fermentation (black). Results from the cut test can only reveal the flavor of the cocoa beans qualitatively. Slaty beans usually impart a strong astringency and have a sour taste with little cocoa and bouquet flavor while purple beans usually have a bitter and harsh taste. Therefore,

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Table 2.4  Major Off-Flavors in Dried Cocoa Beans CAUSES OF MAJOR OFF-FLAVORS Mold • Over-fermentation • Slow or inadequate drying • Improper storage condition (high RH) • Germinated and damaged beans • Prone to becoming moldy Excessive acid taste • Deep box fermentation • Inappropriate turning • Too rapid drying

Smoky • Contamination by smoke during drying • Exposure of dried beans to smoke Excessive bitterness and astringency • Certain planting materials • Lack of fermentation

Source: Adapted from CAOBISCO. 2015. Cocoa Beans: Chocolate and Cocoa Industry Quality.

the presence of high number of slaty and purple beans is undesirable. However, a too high percentage of fully brown beans is not necessarily an indication of good flavor as there could be the possibility of over-fermentation. Dried cocoa beans with 60% brown beans are usually considered well fermented with the remaining beans preferably purple-brown. Cocoa beans contain more than 400 types of distinct flavor volatiles which are formed during fermentation, drying and roasting (JonfiaEssien et al., 2007). West African cocoa beans, especially those that are produced in Ghana, are in high demand due to their fully developed flavor and strong cocoa aroma (Baker et al., 1994; Jinap, 1994). Premium price is therefore paid for these beans in the international cocoa market due to this quality attribute (Quarmine et  al., 2012). The typical desired flavor associated with good quality cocoa beans is high in cocoa flavor and low in astringency, bitterness and sourness. It is expected that the beans are also free from off-flavors such as smoky, hammy, moldy and putrid. Table 2.4 summarizes the causes of major off-flavors detected in cocoa beans. In summary, a good batch of sufficiently dried cocoa beans should show the following characteristics (McDonald et al., 1981): • Beans having good storage/physical properties • Crisp and plump beans with a shell that is neither broken nor fragile • A well oxidized interior with an adequate brown color within the dried cotyledon (nib)

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• Low in bitterness or astringency flavors • Good flavor without excessive acidity/sourness • Absence of off-flavors 2.5 Latest Developments

The drying methods used in cocoa processing are still relatively crude and very little advancement has been made especially in upgrading the current technologies used. Natural drying under direct sunlight and artificial drying using hot air are still the preferred methods used by the industry. Nevertheless, some studies have been reported by researchers in the development of new drying technologies such as heat pump drying (Hii et al., 2011), adsorption drying (Santhanam Menon et al., 2017) and microwave drying (Mohd Zin and Ibrahim, 2015; Firihu and Sudiana, 2016; Guda et al., 2017). In an attempt to improve the flavor of Malaysian cocoa beans, Hii et  al. (2011) investigated the application of heat pump drying and incorporated it into existing hot air drying. A basic layout of a heat pump dryer is shown in Figure 2.11; it consists of a heat pump system integrated into a drying chamber. The dehumidified air generated from the condenser is conducive for cocoa drying as a result of the mild temperature and low relative humidity conditions. Generally, various literature has indicated that heat pump drying is able to produce dried products of better quality with a reduced energy consumption (Perera and Rahman, 1997; Chua et al., 2002; Mujumdar and Law, 2010; Minea, 2015). Hii et al. (2011) reported a stepwise drying procedure that involved drying initially at an ambient temperature (24 hr), heat pump drying (24 hr) and finally drying using hot air (until fully dried). Significant improvement in Condenser

Dryer

Compressor

Expansion valve

Heated air

Evaporator

Figure 2.11  Schematic of a heat pump drying system.

Cooled air

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the cocoa flavor of Malaysian cocoa beans was observed (high in cocoa flavor and low in sourness), comparable to the flavor of Ghanaian cocoa beans. In addition to heat pump drying, Santhanam Menon et al. (2017) investigated the effects of adsorption drying on cocoa quality. The adsorption dryer consists of adsorption columns that are attached to a drying chamber (Figure 2.12). Zeolite adsorbents are used to dehumidify the air passing through the adsorption columns (RH 15–18%) which is then channeled to the drying chamber. Results have indicated a significant improvement in flavor quality in terms of cocoa flavor, bitterness and astringency as compared to freeze, vacuum and hot air dried cocoa beans. Recently, there have been studies on the use of microwaves in cocoa drying (Mohd Zin and Ibrahim, 2015; Firihu and Sudiana, 2016; Guda et al., 2017). Microwave drying offers advantages such as energy saving, rapid drying rates, shorter processing time, deep penetration

Figure 2.12  Adsorption dryer prototype.

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Table 2.5  Summary of Findings on Microwave Drying of Cocoa Beans EXPERIMENT Comparison among tray dryer, solar cabinet, microwave oven and sun drying

Microwave drying (2.45 GHz) at 600 W, 300 W and 150 W power levels Microwave oven (850 W) at power level set at high, medium and low

Comparison among convective and microwave drying in a two-stage procedure using bean and nib

FINDINGS • The shortest drying time was observed at 0.1 hr (microwave drying) and the longest at 30 hr (sun drying). Tray and solar drying were recorded at 8 and 16 hr, respectively. • Bean acidity was the lowest (high pH value) in microwave dried beans. • Microwave drying showed a faster drying rate than conventional drying. • No constant rate period was observed. • Microwaves positively affect the separation efficiency and physical condition of the wet beans. • Percentage of nibs in shells and shells in nibs showed values below the permitted level at 21.9 and 12%, respectively. • No significant difference in fracturability and hardness among all treatments. • The higher the temperature or microwave power used, the lower the total polyphenols content in dried cocoa samples.

REFERENCES Guda et al. (2017)

Firihu and Sudiana (2016) Hussein et al. (2016)

Mohd Zin and Ibrahim (2015)

of microwave energy, instantaneous and precise electronic control and clean heating processes (Rattanadecho and Maku, 2016; Cao et al., 2017). The mechanisms of microwave heating are based on the rapid polarization and depolarization of charged groups under the action of a microwave field which results in internal heat generation within the product. Application of microwaves in cocoa drying is still at an early stage of R&D where studies are carried out typically using a microwave oven. Studies on the impact of microwave drying on cocoa flavor in published literature are not yet available. Major findings of the related studies are summarized in Table 2.5. 2.6 Concluding Remarks

This chapter has presented the significant role of curing, with particular emphasis on the drying aspects, in the development of flavor and product quality of dried cocoa beans. The importance of flavor remains crucial to chocolate manufacturers, and hence the selection of drying technology is as crucial as the fermentation process during cocoa processing. Sun and hot air drying are typical technologies

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that are still widely used by cocoa farmers, but such technologies still remain crude and lack technological advancement. Nevertheless, recent R&D activities have indicated a potential improvement in quality and possible energy savings through the use of novel techniques such as heat pump, adsorption and microwave drying.

References

Abdullah, K., Wulandani, D., Nelwan, L. O., and Manalu, L. P. 2001. Recent development of GHE solar drying in Indonesia. Drying Technology 19(2):245–256. Abhay, S. M., Hii, C. L., Law, C. L., Suzannah, S., and Djaeni, M. 2016. Effect of hot-air drying temperature on the polyphenol content and the sensory properties of cocoa beans. International Food Research Journal 23(4):1479–1484. Adewumi, B. and Fatusin, A. 2006. Design, fabrication and testing of an impact-type hand operated cocoa pod breaker. Agricultural Engineering International VIII:1–6. Baker, D. M., Tomlins, K. I., and Gay, C. 1994. Survey of Ghanaian cocoa farmer fermentation practices and their influence on cocoa flavour. Food Chemistry 51(4):425–431. Bonaparte, A., Alikhani, Z., Madramootoo, C. A., and Satney, M. 1998. Performance of free convective solar driers for cocoa. Canadian Agricultural Engineering 40(1):23–28. Bravo, A. and Mc Gaw, B. R. 1974. Fundamental artificial drying characteristics of cocoa beans. Tropical Agriculture 51(3):395–406. Camu, N., De Winter, T., Addo, S. K., Takrama, J. S., Bernaert, H., and De Vuyst, L. 2008. Fermentation of cocoa beans: Influence of microbial activities and polyphenol concentrations on the flavour of chocolate. Journal of the Science of Food and Agriculture 88(13):2288–2297. Cao, X., Zhang, M., Fang, Z., Mujumdar, A. S., Jiang, H., Qian, H., and Ai, H. 2017. Drying kinetics and product quality of green soybean under different microwave drying methods. Drying Technology 35(2):240–248. CAOBISCO. 2015. Cocoa beans: Chocolate and cocoa industry quality requirements. http://www.cocoaquality.eu/data/Cocoa20Beans%20Industry%20 Quality%20Requirements%20Apr%202016_En.pdf. (accessed 30 August, 2017). Chinenye, N. M. and Ndukwu, M. C. 2009. Effect of drying temperature and drying air velocity on the drying rate and drying constant of cocoa bean. Agricultural Engineering International XI:1–7. Chua, K. J., Hawlader, M. N. A., Chou, S. K., and Ho, J. C. 2002. On the study of time varying temperature drying – Effects on drying kinetics and product quality. Drying Technology 20(8):1559–1577. Dina, S. F., Ambarita, H., Napitupulu, F. H., and Kawai, H. 2015. Study on effectiveness of continuous solar dryer integrated with desiccant thermal

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storage for drying cocoa beans. Case Studies in Thermal Engineering 5:32–40. Duncan, R. J. E., Godfrey, G., Yap, T. N., Pettipher, G. L., and Tharumarajah, T. 1989. Improvement of Malaysian cocoa bean flavour by modification of harvesting, fermentation and drying method – The Sime-Cadbury process. The Planter 65:157–173. Firihu, M. Z. and Sudiana, I. N. 2016. 2.45 GHz microwave drying of cocoa bean. ARPN Journal of Engineering and Applied Sciences 11(19):11595–11598. Forsyth, W. G. C. and Quesnel, V. C. 1963. The mechanism of cacao curing. In: Advances in Enzymology and Related Areas of Molecular Biology, ed. F. F. Nord, 457–492. Hoboken, NJ: Wiley & Sons. Fuller, R. J. 1993. Solar drying of horticultural produce: Present practice and future prospects. Postharvest News and Information 4(5):131–136. Guda, P., Gadhe, S., and Jakkula, S. 2017. Drying of cocoa beans by using different techniques. International Journal of Agriculture Innovations and Research 5(5):859–865. Hancock, B. L. and Fowler, M. S. 1994. Cocoa bean production and transport. In: Industrial Chocolate Manufacture and Use, ed. S. T. Beckett, 8–24. Glasgow: Blackie Academic and Professional. Hansen, C. E., del Olmo, M., and Burri, C. 1998. Enzyme activities in cocoa beans during fermentation. Journal of the Science of Food and Agriculture 77(2):273–281. Hashim, P., Selamat, J., Muhammad, K., and Ali, A. 1999. Effect of drying time, bean depth and temperature on free amino acid, peptide-N, sugar and pyrazine concentrations of Malaysian cocoa beans. Journal of the Science of Food and Agriculture 79(7):987–994. Hii, C. L., Abdul Rahman, R., Jinap, S., and Che Man, Y. B. 2006. Quality of cocoa beans dried using a direct solar dryer at different loadings. Journal of the Science of Food and Agriculture 86(8):1237–1243. Hii, C. L. and Hussein, H. H. 1997. Development of mobile in-field cocoa pod breaker and bean separator. Paper presented in Malaysian Cocoa Board Internal Seminar, Kota Kinabalu, Sabah, Malaysia. Hii, C. L., Law, C. L., and Cloke, M. 2009. Modeling using a new thin layer drying model and product quality of cocoa. Journal of Food Engineering 90(2):191–198. Hii, C. L., Law, C. L., Cloke, M., and Sharif, S. 2011. Improving Malaysian cocoa quality through the use of dehumidified air under mild drying conditions. Journal of the Science of Food and Agriculture 91(2):239–246. Hii, C. L., Law, C. L., and Law, M. C. 2013. Simulation of heat and mass transfer of cocoa beans under stepwise drying conditions in a heat pump dryer. Applied Thermal Engineering 54(1):264–271. Hii, C. L., Law, C. L., and Suzannah, S. 2012. Drying kinetics of the individual layer of cocoa beans during heat pump drying. Journal of Food Engineering 108(2):276–282. Hii, C. L., Lopez, A. S., and Hussein, H. H. 2002. Design and construction of a fermenter drier prototype for cocoa. Agricultural Mechanization in Asia, Africa and Latin America 33(2):40–42.

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Hii, C. L. and Norhaslita, I. 2006. Design and testing of a mechanical mixer prototype for cocoa drying. Paper presented at The 15th International Cocoa Research Conference, San Jose, Costa Rica. Hii, C. L., and Tukimon, M. B. 2002. Evaluation of fermentation techniques practiced by the cocoa smallholders. The Planter 78(910):13–22. Holm, C. S., Aston, J. W., and Douglas, K. 1993. The effects of the organic acids in cocoa on the flavour of chocolate. Journal of the Science of Food and Agriculture 61(1):65–71. Hussein, H., Ibrahim, M. N., Norashikin, A. A., and Ismail, A. 2016. Microwave application in micronizing wet fermented cocoa beans. In: Proceedings of International Conference on Agricultural and Food Engineering (Cafei2016), ed. S. Abd Aziz et al., 288–297. Serdang: Universiti Putra Malaysia. Jinap, S. 1994. Organic acids in cocoa beans – A review. ASEAN Food Journal 9(1):3–12. Jinap, S., Thien, J., and Yap, T. N. 1994. Effect of drying on acidity and volatile fatty acids content of cocoa beans. Journal of the Science of Food and Agriculture 65(1):67–75. Jinap, S., and Zeslinda, A. 1995. Influence of organic acids on flavour perception of Malaysian and Ghanaian cocoa beans. Journal of Food Science and Technology 32(2):153–155. Jonfia-Eddsien, W. A., Alderson, P. G., and Linforth, R. 2007. Flavour volatiles in dry cocoa beans. In: Proceedings of International Conference on Controlled Atmosphere and Fumigation in Stored Products, eds. E. J. Donahaye, S. Navarro, C. Bell, D. Jayas, R. Noyes, and T. W. Phillips, 593–596. Italy: CAF. Kasran, R., and Ahmad, C. A. 2000. Ultra structural changes during cocoa pod development with specific to abscission zone. Therapeutic 13th International Cocoa Research Conference. https://www.researchgate.net/ publication/282657591_Ultra_structural_changes_during_cocoa_pod_ development_with_specific_to_abscission_zone (accessed 30 August, 2017). Koua, B. K., Koffi, P. M. E., and Gbaha, P. 2017. Evolution of shrinkage, real density, porosity, heat and mass transfer coefficients during indirect solar beans drying of cocoa. Journal of the Saudi Society of Agricultural Sciences doi:10.1016/j.jssas.2017.01.002. Kyi, T. M., Daud, W. R. W., Mohammad, A. B., Wahid Samsudin, M., Kadhum, A. A. H., and Talib, M. Z. M. 2005. The kinetics of polyphenol degradation during the drying of Malaysian cocoa beans. International Journal of Food Science and Technology 40(3):323–331. Lopez, A. S., and Dimick, P. S. 1991. Enzymes involved in cacao curing. In: Food Enzymology, ed. P. F. Fox, 211–236. New York: Elsevier Science Publishers. Malaysia Cocoa Board. 2017. Quality. http://www.koko.gov.my/lkm/industry/ Dry Cocoa Bean Grading Specification.pdf (accessed 30 August, 2017). Mamot, S. 1987. Fermentasi koko I – Faktor-faktor yang mempengaruhinya. Teknologi Koko Kelapa 3(2):15–20.

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McDonald, C. R., Lass, R. A., and Lopez, A. S. F. 1981. Cocoa drying – A review. Cocoa Grower’s Bulletin 31:5–41. Minea, V. 2015. Overview of heat-pump–assisted drying systems, part i: Integration, control complexity, and applicability of new innovative concepts. Drying Technology 33(5):515–526. Minka, C. J. 1986. Potential improvements to traditional solar crop dryers in Cameroon: Research and development. In: Solar Drying in Africa: Proceedings of a Workshop Held in Dakar, Senegal (21–24 July 1986), eds. M. W. Bassey, and O. G. Schmidt, 11–22. Ottawa: IDRC. Misnawi, Jinap, S., Jamilah, B., and Nazamid, S. 2004. Sensory properties of cocoa liquor as affected by polyphenol concentration and roasting duration. Food Quality and Preference 15:403–409. Mohd Zin, N. F. A., and Ibrahim, N. A. 2015. The effects of two-stage drying of cocoa beans/nibs on selected quality parameters. In: Proceedings of the 8th Asia Pacific Drying Conference, eds. C. L. Law, C. L. Hii, S. P. Ong, C. L. Chiang, P. L. Show, and I. Khoiroh, 337–344. Kuala Lumpur: University of Nottingham Malaysia Campus. Mujumdar, A. S., and Law, C. L. 2010. Drying technology: Trends and applications in postharvest processing. Food and Bioprocess Technology 3(6):843–852. Perera, C. O., and Rahman, M. S. 1997. Heat pump dehumidifier drying of food. Trends in Food Science and Technology 8(3):75–79. Quarmine, W., Haagsma, R., Sakyi-Dawson, O., Asante, F., van Huis, A., and Obeng-Ofori, D. 2012. Incentives for cocoa bean production in Ghana: Does quality matter? NJAS – Wageningen Journal of Life Sciences 60–63:7–14. Rattanadecho, P., and Makul, N. 2016. Microwave-assisted drying: A review of the state-of-the-art. Drying Technology 34(1):1–38. Said, M. 1982. Perubahan kimia dan biokimia semasa pemprosesan koko. Teknologi Pertanian 3(1):11–27. Santhanam Menon, A. S., Hii, C. L., Law, C. L., Shariff, S., and Djaeni, M. 2017. Effects of drying on the production of polyphenol-rich cocoa beans. Drying Technology 35(15):1799–1806. Teh, Q. T. M., Tan, G. L. Y., Loo, S. M., Azhar, F. Z., Menon, A. S., and Hii, C. L. 2016. The drying kinetics and polyphenol degradation of cocoa beans. Journal of Food Process Engineering 39(5):484–491. Wan Daud, W. R., Mcor Talib, M. Z., and Hakimi lbrahim, M. 1996. Characteristic drying curves of cocoa beans. Drying Technology 14(10):2387–2396. Wessel, M., and Quist-Wessel, P. M. F. 2015. Cocoa production in West Africa, a review and analysis of recent developments. NJAS – Wageningen Journal of Life Sciences 74–75:1–7. Wood, G. A. R. 1985. From harvest to store. In: Cocoa (4th edition), eds. G. A. R. Wood and R. A. Lass, 444–504. New York: Longman Inc.

3 Roastin g E quipment for C ocoa P roces sin g M I S N AW I , N O O R A R I E FA N D I E F E B R I A N T O A N D A R IZ A BU DI T U N J U NG SA R I Contents

3.1 Introduction 47 3.2 Theory of Cocoa Roasting 48 3.2.1 Whole Bean, Nibs and Liquor Roasting 48 3.2.2 Discoloration 50 3.2.3 Fat Loss 51 3.2.4 Maillard Reaction 51 3.3 Selection of Cocoa Roasters 53 3.3.1 Small-Scale and Pilot Plant Equipment 54 3.3.2 Industrial-Scale Equipment 55 3.4 Novel Roasting Equipment 57 3.4.1 Gourmet Roaster 57 3.4.2 Integrated Debacterization 57 3.4.3 Downsized Equipment 59 3.5 Concluding Remarks 59 References 60 3.1 Introduction

Roasting is one of the most important operations in cocoa and chocolate processing, and it is important to the development of flavor that will determine the quality and improve the palatability of the finished chocolate products. Typically, heating at high temperature alters the sensory properties and expands the range of tastes, aromas and textures associated with the food. Roasting also facilitates food preservation by destroying microorganisms, degrading enzymes and reducing water activity that could prevent post-roasting microbial growth. The definition of roasting can be equated to baking; in common usage, 47

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baking is usually applied to flour-based foods or fruits, whereas roasting is for meats, nuts and vegetables. However, both processes use heated air as a medium and are utilized to alter the eating quality of foods (Fellows, 2000). Due to the lingering taste of bitter and astringent flavors, cocoa in its natural taste (without roasting) is not desirable for consumption. Changes that occur during roasting in terms of chemical (flavor development) and physical/structural changes are important development stages prior to subsequent chocolate production. The structural changes that occur during cocoa roasting were investigated by de Brito (2001) who observed that roasting generated more ruptured cells in the cocoa beans. Along with a low moisture content in the shell and nibs during roasting, the ruptured cells thus ease subsequent processes such as deshelling, grinding and butter pressing. Microbiologically, roasting helps to reduce the number of microorganisms under the intense heating process (Afoakwa, 2010), especially when the cocoa beans are obtained from various sources which could have a diverse microorganism content. With the growing concern of mycotoxin contamination in cocoa beans, particularly ochratoxin A (OTA), roasting also offers a significant advantage in reducing the content of OTA in the cocoa beans. Copetti et al. (2013) reported that roasting at 140°C for 15 min could reduce as much as 85.7% of the OTA. Today, the science of cocoa roasting has developed rapidly as well as the technology associated with it. The development of distinct flavor characteristics and specific flavor notes are now possible through manipulation of the roasting process, and this has become of great interest in the chocolate industry. The development of cocoa roasters equipped with technologically innovative features that can determine optimum roasting conditions based on the cocoa bean or nib characteristics contribute significantly to the cocoa industry. Furthermore, new heating technology opens the possibility of roasting using infrared microwaves and superheated steam. 3.2 Theory of Cocoa Roasting 3.2.1 Whole Bean, Nibs and Liquor Roasting

Whole bean roasting is economically feasible for small- to mediumscale industry, since it requires only simple equipment and has only a

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few working steps which means smaller capital investment in machinery and also labor cost. For large-scale industry that intends to produce premium quality chocolate, whole bean roasting may be applied to preserve the delicate aroma. The presence of an intact shell will protect nibs from losing aromatic compounds (Kamphuis, 2009). It is also easier to remove shells from the nibs after roasting rather than doing so on the unroasted beans. Roasted bean deshelling may be done with only simple cracking and exhausting devices. However, there are several disadvantages to the application of whole bean roasting. Uneven roasting may occur due to variation in bean sizes leading to inefficient heat transfer. Restricted vaporization inhibits the removal of undesirable volatiles and induces migration of cocoa butter from the nib to the shell (Kleinert, 1994; Urbanski, 1989). Furthermore, whole bean roasting allows the attachment of foreign materials to the shells, whereas pyrolytic products from these materials can contaminate the flavor of cocoa liquor (Kleinert, 1994). Thus, it is recommended that bean sorting and grading is performed prior to roasting to ensure optimum and unpolluted roasting. Alternatively, cocoa nibs can be separated from the shells and subject to roasting. Nib roasting is widely applied in grinding industries since it allows for the adjustment of different characteristics of the cocoa products. The process allows for modifications such as alkalization, acidification or the addition of specific ingredients to the nibs prior to roasting aiming to obtain the specific character of cocoa powder. In addition, nib roasting could also preserve the butter content in cocoa nibs since there will be no fat migration to the shell. The roasting process runs at a shorter time due to the rapid water evaporation and uniform heat distribution (Dimick and Hoskin, 1981). Moreover, it offers flexibility in blending various types of bean while still maintaining a consistent roasting quality. The major drawback for nib roasting is that additional equipment is required to separate the nibs from the shells prior to roasting. Shell removal can be done initially by utilizing a micronizer with infrared exposure, hot air or saturated steam treatments (Kleinert, 1994). The purpose of the treatment is to loosen the shell from the nib. The heat treatment causes the shell to lose its rigidity and that it can be broken easily (Minson, 1992). Up to 40% of the total energy during roasting is used to heat the shell (Thorz and Shmitt, 1984).

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Table 3.1  Characteristics of Three Different Cocoa Roasting Methods CHARACTERISTICS Flavor development Flavor profile modification through alkalization or blending Extract undesirable volatiles Loss of fat to shell Obtain microbial kill Loosen shell Good grindability

WHOLE BEAN ROASTING

NIB ROASTING

MASS/LIQUOR ROASTING

⊕ ∅

⊕ ⊕

⊕ Δ

∅ ∅ ⊕ ⊕ ⊕

⊕ ⊕ ⊕ * ⊕

⊕ ⊕ Δ * ∅

Source: Adapted from Kleinert, 1994. “Cleaning, roasting and winnowing,” Industrial Chocolate Manufacture and Use 55–69. “⊕” Favorable; “Δ” medium; “∅” poor; “*” need preliminary thermal treatment.

Alternatively, a business could choose mass or liquor roasting over nib roasting. Similar to nib roasting, shell removal should be done before grinding. The liquor is then heated and roasted using relatively inexpensive and simple equipment employing a scraped surface heat exchanger (Kleinert, 1994). However, its colloidal state (mainly cocoa butter and solid) is not effective for microbial decontamination as compared to the former two methods. Cocoa liquor has a larger particle surface which is desirable for off-flavor vaporization. Consequently, this process may produce moderate flavors and to some extent reduce conching times (Kleinert, 1994). This property is favored by businesses since conching consumes the longest processing time in chocolate making or SME industries with a limited number of conching machines. A summary of the advantages and the disadvantages of different roasting methods is shown in Table 3.1. 3.2.2 Discoloration

As roasting is a heat-induced process, it could affect the color of the roasted product. Additional roasting time and temperature lead to a darker color in the cocoa beans due to the Maillard non-enzymatic reactions. The change in color should be carefully monitored since it will affect the appearance of the final product. Classification of the roasting degree in cocoa is not as developed as for coffee, which has many terms such as light, medium and full roast, and is further classified into various styles including cinnamon roast (195°C), New

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England roast (205°C), American roast (210°C), City roast (220°C), Full city roast (225°C), Vienna roast (230°C), French roast (240°C), Italian roast (245°C) and Spanish roast (250°C) (Bollinger, 2013; Sweetmaria’s, 2013). Afoakwa (2010) suggested that bean characteristics greatly influence color after roasting. Minimum discoloration will occur in cocoa beans with a light cotyledon color, a class of cocoa from Criollo or Trinitario varieties which is appreciated for its fine flavor. The light yet vibrant color will alter consumer perception who may perceive the chocolate to be less bitter since a dark color is always associated with stronger bitterness. The color of roasted cocoa beans may be manipulated through the roasting process. By changing the pH using acid or base substances, different color tones can be obtained. Alkalization using base/alkaline, commonly referred to as the Dutch process, is used to create a darker color in cocoa liquor and powder while reducing the original acidic note in the beans. Darker cocoa powder is preferred in beverage and bakery industries since dark brown is usually associated with more chocolate in the products. 3.2.3 Fat Loss

Fat loss is often considered as the main reason for avoiding whole bean roasting considering the fact that cocoa butter has a higher commercial price than cocoa powder. Large-scale businesses invest in infrared micronizers for shell removal to prevent loss of the butter during roasting. Despite the risk of losing butter, whole bean roasting is still preferred by SME due to the lower capital investment in equipment. The degree of fat loss during roasting of whole cocoa beans is affected by the type of roaster. Convective-type roasters such as ones with a tunnel and forced airflow could lower butter content in roasted beans and also in drum-type roasters due to the dynamic movement of beans and intense airflow (Krysiak et al., 2003). In contrast, microwave heating may improve butter preservation during roasting (Krysiak, 2011). 3.2.4 Maillard Reaction

Maillard non-enzymatic browning can be considered as the main reaction in cocoa roasting which essentially produces flavor compounds

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contributing to the chocolate flavor. Hoskin and Dimick (1994) previously mentioned that roasting understandably deserves considerable attention. Prior to roasting, cocoa beans may taste astringent, bitter, acidy, musty, unclean, nutty or even chocolate-like depending on the origins and preparation methods. After roasting, the bean possesses a typical intense aroma of cocoa, although remaining unpalatable. Nursten (2005) reported a study compromising several changes that occurred during the Maillard reaction, and which was divided into three main stages (Table 3.2). The initial stage of the Maillard reaction provides no contribution to the development of flavor and off-flavor as well as the discoloration of the roasted product. However, the aforementioned effect was reported as occurring during the intermediate and final stage of Maillard reaction. The information provided by Nursten (2005) might be related to the previous findings reported by Mohr et al. (1976) which had demonstrated that slowly reducing the moisture content to about 3% followed by rapid heating to the final roast temperature could optimize the intermediate and final stage of the Maillard reaction. Ziegleder and Oberparleiter (1996) also proposed that the optimization of the Table 3.2  Maillard Reaction Symptoms and Its Intensity during Initial, Intermediate and Final Stages STAGE NO

SYMPTOMS

INITIAL

INTERMEDIATE

1 2 3 4 5 6 7 8 9 10 11

Production of water Loss of vitamin C activity Loss of protein biological value Increasing reducing power Production of fluorescence Development of toxicity Production of carbon dioxide Decreasing solubility Chelation of metals Production of flavor or off-flavor Production of color of discoloration

⊕ ⊕ ⊕ ⊕ ϕ ϕ N/A ϕ ϕ ϕ ϕ

⊕ ϕ ⊕ ⊕ ⊕ N/A ⊕ ϕ N/A ⊕ ⊕

FINAL ⊕ ϕ ⊕ ⊕ ⊕ N/A N/A ⊕ ⊕ ⊕⊕ ⊕⊕⊕

Source: Adapted from Nursten, 2005. The Maillard Reaction: Chemistry, Biochemistry, and Implications. Great Britain: Royal Society of Chemistry. “ϕ” Not occurred. “N/A” Not available.

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Maillard reaction could be done by modifying the roasting temperature and pre-roasting condition such as the addition of moisture prior to the roasting process. Moisture addition resulted in increments of 15% moisture which will then aid the formation of more flavor precursors when heated at 40–60°C (104–140°F) for 10–15 min. The addition of water also helps the flavor precursor to be distributed through the whole area of the beans, and thus in the later stage this will produce a more distributed flavor compound. The process is then continued at a higher temperature of 98–110°C (208–230°F) until the moisture content of the bean reaches 3%. Upon roasting, this gives a product with a more intense flavor compared with normal roasted beans since the intermediate and final stage of the Maillard reaction is optimized. In the final stage of the Maillard reaction and at an elevated temperature, depending on the substrates and the pH, the intermediate compounds of the oxygenated sugar degradation products will polymerize to produce heterocyclic compounds; which in turn contribute to the final flavor. Some of the most important compounds are pyrazines, pyrroles, pyridines, imidazoles, thiazoles and oxazoles. The significance of the term “browning reaction” is derived from this final stage; only then will the insoluble dark brown pigments called melanoidins be produced. The most interesting part of Nursten’s (2005) work is that it also mentioned the development of toxicity during the Maillard reaction, yet this was still uncertain especially in the intermediate and final stages of Maillard reaction. Some research has reported that carcinogenic compounds such as acrylamide could be produced through the Maillard reaction (Farah et al., 2012). Acrylamide is considered as a human carcinogen compound due to the interactions between asparagines and dicarbonyl compounds (Becalski et al., 2003; Sander et al., 2002; Yasuhara et al., 2003; Zyzak et al., 2003). Although the safe level of acrylamide in the cocoa product has not been determined yet, it has been shown to be carcinogenic and might cause damage to the nervous system. 3.3 Selection of Cocoa Roasters

Krysiak et al. (2013) indicated that in addition to time and temperature, airflow rate and velocity are also factors contributing to

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successful roasting. Airflow drives temperature distribution and water evaporation, thus enhancing heat and mass transfer. At the same temperature and roasting duration, a different outcome is expected from a convection oven and a rotating drum roaster. Therefore, roasting equipment selection is important for guaranteeing the desired product quality. 3.3.1 Small-Scale and Pilot Plant Equipment

In the small-scale production of chocolate, any type of heat-induced roaster could be applied to obtain roasted cocoa beans or nibs. Simpler and more compact roaster machines are preferred due to their simplicity and the small quantity of bean processed. In the production of the traditional chocolate product of Tablea in the Philippines, the use of iron or stainless steel frying pans is a common practice since no major investment is required by the producers. However, since the process requires manual control, highly trained and experienced operators are required. In this case, a convection oven offers easier control with a temperature setting that can be easily adjustable manually. The new generation oven even has user-friendly temperature programming with an automated shutdown. This reduces the labor requirement due to the minimally monitored operation. On the other hand, the use of simple microwave equipment can also be an alternative for small-scale producers. As mentioned by Yoshida and Kajimoto (1994), microwave roasting offers a significantly shorter production time, and heating is more uniform as compared to conventional roasting. Over time, the development of equipment that combines both the function of a microwave and a steam cooker also opens up the possibility of roasting using superheated steam (SHS). Zzaman and Yang (2014) reported that the use of SHS in cocoa roasting could preserve the color and textural properties of cocoa beans. Furthermore, SHS roasting offers a shorter roasting time that could prevent the loss of essential volatiles and the prevalence of bitterness due to long roasting duration. However, despite the numerous alternatives of roaster that can be offered to small-scale production, it can’t be denied that a drum (cylindrical) type roaster is still the preferred choice for roasting cocoa beans. Drum-type roasters that use indirect heating by means of

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Figure 3.1  Small-scale 1 kg (left) and 10 kg (right) whole bean roaster powered by gas. (From Indonesian Coffee and Cocoa Research Institute.)

convection/steam or direct heating using gas, coal or electric heating plates have become a popular choice due to their ability to produce uniform roasting and flexibility with controlling the process. Furthermore, the variability in the design and the attractiveness during its operation often become the main selling point to small-scale businesses for obtaining the authentic roasting experience that can be offered to the customers. Currently, small capacity roasters typically used for coffee (300 gm – 50 kg per batch) have become a popular choice among chocolate producers in Indonesia since they are attractive and affordable (Figure 3.1). 3.3.2 Industrial-Scale Equipment

The main differences in small-scale processing compared to industrial processing is mainly in its quantity. In the handling of such large material quantity, special attention should be paid to disinfection properties, heating uniformity and roasting time. In big-scale roasters, the design usually consists of a steam or water generator, which is absent in small-scale roasters, with the purpose of adding moisture to the material. The addition of moisture during roasting will generate steam to improve the effectiveness of microbial killing thus ensuring significant microbial reduction. Another significant difference in industrial processing is the option to carry out roasting continuously instead of in batches. The continuous system is usually carried out

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using roasters equipped with series of slats heated by indirect hot air. These series of titled slats turn at a predetermined time, thus allowing the beans in each slat to roast sufficiently within the traveling period from the feed inlet to the outlet (Beckett, 2009). Another advance to continuous roasting is the development of a metal conveyor belt combined with the indirect and direct heating types of roaster. The use of a metal conveyor facilitates a continuous roasting process whereby processing time is adjusted by varying the speed of the conveyor belt. However, there exists a difficulty in ensuring a uniform heat distribution since the continuous system is in fact a semi-closed system and allows the input of fresh and high moisture content materials, heat loss to the surroundings and the development of steam could affect the temperature distribution inside the roaster. Thus, it is important to ensure uniform heat distribution in order for the roasting process to progress in optimal conditions. Apart from heating, the continuous roaster is also equipped with a continuous cooling system that ensures the rapid cooling of the material prior to exiting the roasting system. Rapid cooling is needed to loosen the shells of the cocoa beans prior to the deshelling process. Steam roasters have been developed to enhance the heat distribution in large-scale processing, but Zipperer (1915) reported that it failed to perform thorough roasting as expected. On the other hand, indirect heating using hot air is more popular compared to direct heating which exposes the beans to the risk of burning or getting charred. Apparently, the industrial roasting process using hot air normally lasts between 45 min and 1 hr. On the other hand, a recent approach using liquor roasting in order to improve the efficiency in the subsequent conching process is also available. However, due to the nature of cocoa liquor which is significantly affected by bean characteristics and origins as well as moisture content, material handling in liquor roasting is more challenging than other methods. Beckett (2009) found that the reaction between water and the cellulose-protein-fat system in cocoa liquor significantly affects the characteristic of the cocoa liquor. Too much moisture will result in formation of a thick paste whereas too low moisture will affect the chocolate flavor produced. Thus, moisture control is crucial when using a cocoa liquor roasting method.

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3.4 Novel Roasting Equipment

Coffee roasting equipment has greatly evolved due to the blooming growth of coffee shops and coffee beverage consumption worldwide. The innovation is mainly driven by the need for easier operation; to make coffee roasting more customizable and controllable. The recent generation of coffee roasters is equipped with computerized monitoring which enables real-time measurement on both temperature and color development. This feature coupled with continuous data acquisition allows the operator to evaluate the roasting parameters and flavor characteristics, and eventually to decide the best roasting condition for the various type of coffee beans. 3.4.1 Gourmet Roaster

With the diverse sources of cocoa beans and the demand for specialty chocolate by consumers, roasting can no longer be generalized. This requirement can be met by using gourmet roasters which allow finetuned roasting. The user can enter the desired setting into a computerized interface to modify several parameters such as temperature, roasting time, airflow, steam injection and cooling time. The roaster is operated in batch mode with convective air roasting. Gentle fluidization is applied to ensure uniformity in heat distribution. Such roasters are available on the market such as Solano from Buhler, NeoGourmet by Neuhaus Neotec and OPUS series by Lilla. 3.4.2 Integrated Debacterization

Given the low moisture content, cocoa beans and chocolate products are at low risk of spoilage. Nevertheless, cocoa beans are still a favorable habitat for yeasts and molds from which heat-resistant spores are released. Salmonella exists in cocoa beans and could contaminate the final products. Debacterization is an attempt to reduce microbial contamination in food, and successful debacterization is indicated by a reduction in the microbial count. Industrial debacterization uses steam that is injected into the beans. As an alternative for small- and medium-sized industries, this can be carried out by putting a covered basket of cocoa beans over a double boiler and exposing the beans to the steam. Another potential approach is to use gamma irradiation, which is used in fruit sterilization.

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Stobinska et al. (2006) performed debacterization using a convective oven by placing a single layer of cocoa beans at a temperature of 150°C and relative humidity of 5%. This method was found effective in reducing bacterial count from 4.8 × 106 to 2.0 × 104 CFU/g. The lower microbial count was achieved by using pressurized steam. This was applied in the so-called “Buhler method” that employs high pressurized steam at 300–550 kPa at a temperature range of 130–250°C. The debacterization process could be accomplished in 0.5–5 min (Chronopoulos et al., 2011). In terms of the effect of steam treatment on the chocolate aroma, Krysiak et al. (2007) reported that roasting at a higher relative humidity (2.0 and 5.0%) as compared to low relative humidity (0.4%) did not significantly change the constituents of the volatile compounds of the roasted cocoa beans. The flavor active compounds such as methylhydrazine, 2,5-dimethylpyrazine, 2,6-dimethylpyrazine and 2-ethyl6-methylpyrazine were not significantly different between high and low relative humidity roasting conditions (Table 3.3). The newer generation of roasting equipment features integrated steam debacterization. Debac™ is a debacterization system by Buhler Barth GmbH (Germany) which offers an effective sterilization step without affecting the chocolate aroma. In this system, steam Table 3.3  Pyrazine Concentrations after Cocoa Bean Roasting at Different Relative Humidity* PARAMETERS Relative humidity (% RH) Roasting time (min) Temperature (°C) Methylpyrazine 2,6-Dimethylpyrazine ethylpyrazine 2,3-Dimethylpyrazine 2-Ethyl-5-methylpyrazine 2-Ethyl-6-methylpyrazine trimethylpyrazine 2-Ethyl-3,6-dimethylpyrazine

ROASTED COCOA BEANS 0.4 135 35 3.3b 1.84b 0.65b 0.3 0.11 0.51b 0.01 0.51b

2.0 135 45 3.73ba 1.93b 0.69b 0.21 0.18b 0.6b 0.93b 0.65b

RAW COCOA BEANS

5.0 135 60 3.96a 2.0b 0.62b 0.48 0.2b 0.47b 1.01b 0.52b

– 20 – traces 0 0 0.08 0.05 traces 0.04 0.07

Source: Adapted from Krysiak et al. 2007. “Anais effect of relative and humidity on the content of volatile compounds in roasting cocoa beans,” Focus on Food Engineering Research and Developments 467–482. *  Values in each line showing the same letter are not significantly different (p > 0.05).

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is introduced after roasting where the beans are in contact with the steam at up to 500 kPa. The bacterial plate count was reported less than 5  ×  103  CFU/g (Buhler, 2018). A smaller-scale roaster with steam injection is provided by Unox (Italy) with a temperature setting starting from 48°C up to 260°C (Unox, 2018). Zzaman and Yang (2013) reported that roasting was successfully carried out using superheated steam at 200°C for 10 min with pyrazines as the main aroma constituent. 3.4.3 Downsized Equipment

Artisanal or crafted chocolate is an emerging niche market with remarkable growth. The products are exotically tailored, and bean materials are sourced directly from farmers. Instead of melting and molding using store-bought chocolate, the crafters instead implement the bean-to-bar approach. They buy whole cocoa beans and diligently follow proper chocolate-making steps from roasting to tempering. For this market segment, a roaster which is dedicated to crafters handles less than 15 kg of cocoa beans in a batch system. A relatively small size CocoaT junior roaster works with at least 2 kg beans (Cocoatown, 2017). Electric or gas may be installed to generate heat for roasting. A gas burner allows flexible temperature setting such as in the rotated drum roaster developed by Cacao Cucina (Cacaocucina, 2015). Modularity and space saving are important factors in setting up artisanal chocolate-making facilities at home. A chocolate processing line was developed by Jaf Inox for handling 10 kg beans in a small industrial layout (Jaf Inox, 2017). A basic beans-to-bars unit from Selmi requires 7 m length space and is comprised of seven individual machines (Selmi, 2018). An interesting design by Domori (2017) incorporates Tecno3 and combines all units into one entity. The compact device requires a very small space (2 × 1 m), while at the same time enables disassembly for easy cleaning. 3.5 Concluding Remarks

Roasting is the crucial step for flavor development in cocoa beans, and the selection of roasting methods and equipment need to be

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taken into serious consideration in order to adapt with changes in bean origins and consumer trends. The newer generation of roasters emphasize food safety, and consequently debacterization has now become an integrated feature in modern roaster design. Consumers growing appreciation toward cocoa origins has led to the development of smaller batch equipment with highly individualized roasting conditions to support gourmet roasters. In addition to that, the growing trend of bean-to-bar industry demands the downsizing of conventional equipment which has a higher production capacity. Flavororiented roasting that incorporates volatile analysis instrumentation or artificial intelligence might be the key advancements in future roaster design. Possibilities are therefore open for the invention of a smart cocoa roaster that enables product personalization.

References

Afoakwa, E. 2010. Chocolate Science and Technology. Chichester, UK: John Wiley & Sons, Ltd. Becalski, A., Lau, B.P., Lewis, D., and Seaman, S.W. 2003. Acrylamide in foods: Occurrence, sources, and modelling. Journal of Agricultural and Food Chemistry 51:802–808. Beckett, S.T. 2009. Industrial Chocolate Manufacture and Use. UK: John Wiley & Sons, Ltd. Bollinger, D. 2013. Degree of roast. http://www.homeroasters.org/index.htm (accessed 28 February, 2013). Buhler. 2018. Debacterizing system DebacTM. www.buhlergroup.com (accessed 17 February, 2018). CacaoCucina. 2015. Cocoa bean roaster model RO-15. http://cacaocucina. com (accessed 17 February, 2018). Chronopoulos, D., Zuurbier, R., Brandstetter, B., and Jung, C. 2011. Food comprising alkalized cocoa shells and method therefor. U.S. Patent Application 12642595. https://patentscope.wipo.int (accessed 17 February, 2018). Cocoatown. 2017. CocoaT junior roaster SS. https://cocoatown.com (accessed 17 February, 2018). Copetti, M.V., Iamanaka, B.T., Nester, M.A., Efraim, P., and Taniwaki, M.H. 2013. Occurrence of ochratoxin A in cocoa by-products and determination of its reduction during chocolate manufacture. Food Chemistry 136:100–104. de Brito, E.S., García, N.H.P., Gallão, M.I., Cortelazzo, A.L., Fevereiro, P.S., and Braga, M.R. 2001. Structural and chemical changes in cocoa (Theobroma cacao L) during fermentation, drying and roasting. Journal of the Science of Food and Agriculture 81:281–288.

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Dimick, P.S., and Hoskin, J.M. 1981. Chemico-physical aspects of chocolate processing-a review. Canadian Institute of Food Research and Technology Journal 4:269–281. Domori. 2017. Bean to bar machine: The first compact machine for making chocolate is created. https://press.domori.com (accessed 17 February, 2017). Farah, D.M.H., Zaibunnisa, A.H., and Misnawi. 2012. Optimization of cocoa beans roasting process using response surface methodology based on concentration of pyrazine and acrylamide. International Food Research Journal 19:1355–1359. Fellows, P. 2000. Food Processing Technology Principles and Practice. UK: Woodhead Publishing Limited. Hoskin, J.C., and Dimick, P.S. 1994. Chemistry of flavour development in chocolate. In: Industrial Chocolate Manufacture and Use, ed. S.T. Beckett, 102–115. New York, NY: Springer. Jaf Inox. 2017. Bean to bar line 10 Kg Batch. https://jafinox-rdw.com (accessed 17 February, 2017). Kamphuis, H.J. 2009. Production and quality standards of cocoa mass, cocoa butter and cocoa powder. In: Industrial Chocolate Manufacture and Use (4th edition), ed. S.T. Beckett, 121–141. Chichester, UK: John Wiley & Sons Ltd. Kleinert, J. 1994. Cleaning, roasting and winnowing. In: Industrial Chocolate Manufacture and Use, ed. S.T. Beckett, 55–69. New York, NY: Springer. Krysiak, W. 2011. Effects of convective and microwave roasting on the physicochemical properties of cocoa beans and cocoa butter extracted from this material. Grasas y Aceites 62:467–478. Krysiak, W., Adamski, R., and Żyżelewicz, D. 2013. Factors affecting the color of roasted cocoa bean. Journal of Food Quality 36:21–31. Krysiak, W., Iciek, J., and Motyl-Patelska, L. 2003. Effect of roasting conditions on selected physicochemical properties of roasted cocoa beans. Inzynieria Chemiczna i Procesowa 24:509–523. Krysiak, W., Majda, T., and Nebesny, E. 2007. An effect of relative and humidity on the content of volatile compounds in roasting cocoa beans. In: Focus on Food Engineering Research and Developments, ed. N.P. Vivian, 467–482. New York, NY: Nova Science Publisher. Minson, E. 1992. Chocolate manufacture-beans through liquor production. The Manufacturing Confectioner. http://www.gomc.com/eSub/framesetmc.asp (accessed 7 February, 2018). Mohr, W., Landschreiber, E., and Severin, T.H. 1976. On the specificity of cocoa aroma. Fette Seifen Anstrichmittel 2:88–95. Nursten, H.E. 2005. The Maillard Reaction: Chemistry, Biochemistry, and Implications. Great Britain: Royal Society of Chemistry. Sander, R.A., Zyzak, D.V., Stojanovic, M., Tallmadge, D.H., Ebert, B.L., and Ewald, D.K. 2002. An LC/MS acrylamide method and its use in investigating the role of asparagine. Acrylamide symposium, In: 116th Annual AOAC International Meeting, Los Angeles, CA, September 2002. Gaithesburg: AOAC.

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Selmi. 2018. Bean to bar, configurazione a fondente. www.selmi-chocolate.it (accessed 7 February, 2018). Stobińska, H., Krysiak, W., Nebesny, E., and Kozanecka, E. 2006. Effects of convective roasting conditions on microbial safety of cocoa beans. Acta Agrophysica 7:239–248. Sweetmaria’s. 2013. Using Sight to Determine Degree of Roast. https://www. sweetmarias.com/library/content/using-sight-determine-degree-roast (accessed 28 February, 2013). Thorz, M., and Shmitt, A. 1984. Thin film liquor roasting and pre-treatment technology. Manufacturing Confectioner 64:65–70. Unox. 2018. Steam plus. www.unox.com (accessed 17 February, 2018). Urbanski, J.J. 1989. Cocoa roasting. Manufacture Confectioner 11:58–62. Yasuhara, A., Tanaka, Y., Hengel, M., and Shibamoto, T. 2003. Gas chromatographic investigation of acrylamide formation in browning model systems. Journal of Agricultural and Food Chemistry 51:3999–4003. Yoshida, H., and Kajimoto, G. 1994. Microwave heating affects composition and oxidative stability of sesame (Sesamum indicum) oil. Journal of Food Science 59:613–616. Ziegleder, G., and Oberparleiter, S. 1996. Aromaentwicklung in Kakao. Susswaren 40:22–24. Zipperer, P. 1915. Manufacture of Chocolate and Other Preparations. Berlin: Rosenthal & Co. Zyzak, D.V., Sanders, R.A., Stojanovic, M., Tallmadge, D.H., Eberhart, B.L., Ewald, D.K., Gruber, D.C., Morsch, T.R., Strothers, M.A., Rizzi, G.P., and Villagran, M.D. 2003. Acrylamide formation mechanism in heated foods. Journal of Agricultural and Food Chemistry 51:4782–4787. Zzaman, W., and Yang, T.A. 2013. Effect of superheated steam and convection roasting on changes in physical properties of cocoa bean (Theobroma cacao). Food Science and Technology Research 19:181–186. Zzaman, W., and Yang, T.A. 2014. Moisture, color and texture changes in cocoa seeds during superheated steam roasting. Journal of Applied Sciences Research 9:1–7.

4 Fl avo r D e v elopment durin g C ocoa R oastin g SUZA NNA H SH AR IF Contents

4.1 Overview of Cocoa Roasting 63 4.2 Flavor Development during Cocoa Roasting 66 4.2.1 Chemical Compounds in Cocoa Aroma 68 4.2.2 Alkalization Effects 72 4.3 Methods for Analyzing Flavor Compounds 74 4.3.1 Flavor Index 74 4.3.2 Simultaneous Extraction–Distillation Techniques of Likens–Nickerson 75 4.3.3 Headspace Solid-Phase Microextraction (HS-SPME) 76 4.3.4 Inline Roasting-Cooled Injection System Hyphenated with Gas Chromatography–Mass Spectrometry (ILR-CIS-GC-MS) 78 4.4 Risk of Contaminant Formation 79 4.4.1 Acrylamide 79 4.4.2 Biogenic Amine 82 4.5 Concluding Remarks 83 References 84 4.1 Overview of Cocoa Roasting

Roasting is defined as a high-temperature process, and it is commonly applied to a wide variety of agriculture products such as cocoa, coffee and nuts such as almond, pistachio, and so on. Basically, the roasting process is carried out to achieve several purposes namely the removal of undesirable compounds with low boiling points such as acetic acid and the formation of the typical roasted sweet odorant of cocoa (Keeney, 1972). These will finally contribute to the formation of the cocoa flavor which is an essential attribute of cocoa quality. The flavors 63

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produced during roasting come from a combination of 400–500 compounds (Ziegleder, 2009). These compounds include aldehydes and pyrazines, which are formed during roasting through the Maillard reaction and Strecker degradation of amino acids and sugars (Heinzler and Eichner, 1991). Manufacturers face a big challenge to process cocoa beans, which can originate from many different sources, and they most probably have no knowledge of the processes the cocoa beans had been subjected to. Physically the beans can be graded based on observable traits such as bean size, fermentation level, bean count, evidence of infestation, germination of beans, and so on. However, the level of flavor precursors, such as sugar content, amino acid content, polypeptides, and so on, is harder to evaluate. In order to maximize/optimize the potential of the cocoa beans, on-farm practices such as fermentation and drying are crucial. The development of a fast technique using near-infrared spectroscopy may allow for quicker prediction of biochemical quality parameters such as phenolic substances, organic acid, epicatechin, lactic acid as well as fermentation time and the pH value of the cocoa beans (Krähmer et al., 2015). Saltini et al. (2013) proposed that if a batch of raw material is very heterogeneous, it is inevitable that flavor potential is to some extent wasted. They suggested a way to overcome the problem of heterogeneity through the standardization of farmers’ activities and implementation of a traceability system where chocolate manufacturers receive data on how the cocoa beans have been processed, and processing parameters will be optimized for each group of similar cocoa beans, that is, farm, country, type of processing, and so on. Recent findings show that a totally different approach, where fermentation time was flexible and dependent on the farmer’s experience to stop fermentation, was able to produce cocoa beans with a better aroma. It was also proposed that bulk cocoa can attain fine flavor cocoa bean standards through pretreatments (Eskes et al., 2017). Sustainable cocoa production involves the production of highquality cocoa beans which are made up of several components such as flavor volatiles, nutritional composition, polyphenolic content and fermentative quality (Kongor et  al., 2016). The most important are the flavor volatiles of the beans as these affect the cocoa beans acceptability in the market.

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Traditionally, cocoa beans are roasted as whole beans, but cocoa nib roasting and cocoa mass roasting are also practiced commercially (Kleinert, 1994). Each roasting method has differences and is favored by different cocoa processors. Bean roasting is widely used by chocolate manufacturers while nib roasting is more favored by cocoa powder manufacturers. Bean roasting is used to produce cocoa masses with delicate flavors, due to the preservation of the volatile cocoa flavor notes within the shell during roasting (Kamphuis, 2009). Nib roasting is widely used to produce cocoa powders since cocoa nibs can be easily treated with an alkali solution to change the color of the final cocoa powder, or they can be treatment with water or sugar solution for flavor enhancement. Mass or liquor roasting is touted as the most advanced type of roasting and capable of full flavor development due to the optimal temperature distribution (Bauermeister, 1981). Contrary to convective roasting, microwave roasting can reduce the roasting time. Microwave roasting at 700 W for 12.5 min has shown to reduce total acidity and volatile acidity similar to traditional roasting of cocoa beans at 135°C for 35 min (Krysiak, 2011). Moisture treatment has been proposed as a method to improve cocoa flavor. Steam is condensed on the cocoa nibs, resulting in about 15% water addition. This moisture aids the formation of more flavor precursors during the 10–15 min processing time at 40–60°C. After drying to 3% moisture at 98–110°C and roasting, this gives a product with a more intense flavor compared with normal roasted beans. A cocoa aroma profile consists of many different aroma notes, for example acidic, bread-like, caramel-like, cereal, cocoa, coffee-like, dark chocolate, flowery, fruity, honey-like, malty, nutty, roasty, smoky and vegetable-like. A cocoa-specific and nutty-specific aroma component may be generated by proteolysis of the cocoa vicilin-class (7S) globulin by a mixture of cocoa aspartic protease and carboxypeptidase (Voigt et al., 2018). The level of cocoa aroma and nutty aroma produced from this proteolysis varies according to the pH. PH 5.2 produces strong cocoa-specific and strong nutty-specific aroma, while at a lower pH (4.8) a strong cocoa-specific aroma was produced but only a low nuttyspecific aroma. At pH 5.6, only a low level of nutty-specific aroma was detected with no cocoa-specific aroma. However, neither the cocoaspecific aroma and the nutty-specific aroma nor the essential peptide precursors were identified. Based on the oligopeptide sequences

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identified from cocoa vicilin-class globulin proteolysis by aspartic protease and carboxypeptidase, it was concluded that nutty-specific aroma components are produced by slightly longer peptides compared to those responsible for cocoa-specific aroma components (Voigt et al., 2018). Reducing sugar is one of the flavor precursors during the Maillard reaction. A study by de Brito et al. (2001) showed that roasting reduces almost 61% of fructose and 3.2% glucose in dried beans. It is commonly known that reducing sugar is usually the limiting component during cocoa roasting. Fructose injection during roasting was shown to increase the cocoa flavor attribute (Suzannah, 2004). However, the high addition of fructose may lead to an increase in astringency and acidity notes as well as the pH of cocoa liquor. 4.2 Flavor Development during Cocoa Roasting

The roasting of cocoa beans develops the typical roasted and chocolate flavor. It also eliminates undesirable volatiles such as acetic acid which may mask other flavors. Roasting also reduces the moisture content of cocoa beans from around 7% to 1–2%. During roasting, cocoa flavor precursors interact and form flavor compounds which produce the typical intense aroma of cocoa. One of the most important and complex reactions that occurs during roasting is the Maillard browning, non-enzymatic browning or the carbonyl-amine reaction. The Maillard reaction is a common reaction that occurs during the roasting or baking of food products. The caramelization of sugar, roasting of steak and baking of cakes and bread are some examples of the Maillard reaction in food products. In the initial step, a free amino group of amino acids (or protein) attacks the reactive carbonyl group of glucose and fructose forming an N-substituted glucosylamine or a Schiff base and releasing one water molecule. The N-substituted glucosylamine is also called glucosylamine or fructosylamine depending on the initial reducing sugar. The glucosylamine or fructosylamine will undergo tautomerization to 1,2-enaminols and rearrange into isomerization products (Amadori compounds or 1-amino-1-deoxy-2-ketose). These transformed compounds are not detectable by color or flavor change and may be reversible at this stage. This initial reaction is important since many later reactions require the isomerized end products.

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Fructosealanine, a typical aroma precursor detected in cocoa under a roasting condition, decomposes faster with increased temperature and heating time. Meanwhile, the rate of formation of the heterocyclic compound also increases. At higher temperatures and longer roasting times, nitrogen-containing heterocyclic compounds are preferably formed, whereas lower roasting temperatures and shorter roasting times favor the formation of furan derivatives. The main aroma components formed by roasting fructosealanine are 2-acetylpyrrole, 5-methylfurfural and 2-acetylfuran. The composition of aroma compounds is influenced by water activity (aw). With increasing aw values, the yield of pyrazines, pyridines and furan decrease, whereas the amount of pyrroles increases (Heinzler and Eichner, 1991). In the intermediate stage, the isomerization products will undergo different paths depending on the temperature and pH inside the cocoa beans. The intermediate stage involves dehydration, fragmentation and transamination reactions to produce many complex compounds. Under neutral or acidic conditions, the amino compounds are decomposed to 3-deoxyhexuloses that subsequently lose water to give hydroxymethylfurfurals (when hexoses are involved) and other furfural (when pentoses are involved) products. If the pH is neutral or basic, the reactions produce 2,3-enediol and dehydroreductones intermediates, which eventually produces maltol, isomaltol and α-dicarbonyl compounds. The α-dicarbonyl compounds undergo further disintegration (dehydration, fragmentation and transamination) to smaller aldehydes or ketones which are essential to cocoa flavor (Aprotosoaie et  al., 2016). The generation of aroma indicates that reactions have proceeded past the initial stage. Another important route is the Strecker degradation, which leads either to volatile aldehyde, or to volatile pyrazines and other heterocyclic compounds. The Strecker degradation is one of the major pathways for pyrazine formation during the browning reaction. The pyrazine structure is dictated by the side groups on the dioxo compound. For example, the reaction between pyruvaldehyde and valine will produce 2-methylpropanal and 2,5-dimethyl pyrazine, which have been described as having a nutty flavor. In cocoa, the pyrazines are abundantly available and can be used as tracers for the cocoa flavor (Bonvehí, 2005). Recent studies on the Maillard reaction proposed other reaction pathways such as the retro-aldol reaction of Amadori reaction products

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and its dicarbonyl derivatives to produce more reactive C2, C3, C4 and C5 sugar fragments. Three redox mechanisms involving α-hydroxy carbonyls, α-dicarbonyls and formic acid was also suggested. It is also thought that amino acids and sugars undergo independent degradation, in addition to the conventional degradation where the Amadori products are formed leading to the concept of a “chemical pool.” These new reaction pathways suggest that formic acid and acetic acid are the two main degradation products for the Maillard reaction of glucose and fructose (Martins et al., 2001). Although Maillard browning is important, it is highly unlikely that a real food system will consist of only amino acids and sugars. Other compounds such as peptides, proteins, vitamins, fats and their oxidation products and other derivatives may be present and influence the final products. With the different compounds present in cocoa beans, it is impossible to identify all the reactions and pathways that occur during roasting. Therefore, the model system had been used to study the various compounds formed when a single sugar and amino acid were reacted in water or cocoa butter at different temperatures. Melanoidins are the final products of the Maillard reaction. Some of the known properties of melanoidins are that they are brown, have a high-molecular weight, furan ring-containing and nitrogen-containing polymers and may contain carbonyl, carboxyl, amine, amide, pyrrole, indole, azomethine, ester, anhydride, ether, methyl and/or hydroxyl groups. However, the structure of melanoidins has not been fully elucidated (Martins et al., 2001). It is responsible for the color formation and involved in the sensory properties (taste, flavor and texture) of food. Melanoidins increase with roasting time following asymptotic kinetics. High-temperature short-time roasting was found to maximize melanoidins formation (Sacchetti et al., 2016). Melanoidins show remarkable antioxidant activity. Reducing activity and radical-scavenging activity of cocoa increased upon roasting due to the formation of Maillard reaction products (Summa et  al., 2006; Ioannone et al., 2015). 4.2.1 Chemical Compounds in Cocoa Aroma

Cocoa aroma comprises of several hundred compounds present in varying concentrations (0.02–10 mg/kg). Total volatile compounds

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concentration is only 10–200 mg/kg. Heterocyclic aroma constituents represent the greatest amount of the cocoa aroma complex. Main compounds identified were pyrazines, aldehydes, phenols, pyrroles derivatives and furan (Bonvehí, 2005; Ziegleder, 2009). Cocoa powder aroma is primarily composed of low-molecular-weight alcohols, aldehydes, ketones, heterocyclic compounds, esters, hydrocarbons and sulfur compounds. Aliphatic hydrocarbons are not important for aroma, though it may act as precursors of a number of other aroma compounds. Pyrones and furans are formed at moderate temperatures and at relatively high water content which are destroyed during the alkalization process. Most pyrazines are typical roasting products and are generated only from well-dried cocoa beans. Diab et al. (2014) studied the chemical compounds released during the roasting of single cocoa beans using a micro-probe linked to a photo-ionization time-of-flight mass spectrometer. Among the earliest compounds released includes aldehyde (m/z 44), phenylacetaldehyde (m/z 120), caffeine, formyl and/or ethylpyrrole (m/z 95), indole (m/z 117), theobromine (m/z 180) and propylamine (m/z 59). Their study showed that a lot of compounds were released after 10 min of roasting, which coincides with the beginning stage of the Maillard reaction. However, many of the compounds are found naturally present in cocoa beans (e.g., theobromine and caffeine) and not Maillard-reaction products. Cocoa aroma compounds such as aldehydes, ketones and heterocycles were detected. At the end of roasting, resinol derivatives and propene were released which can also indicate over-roasting. Although many compounds made up the cocoa volatile, it is difficult to assess which components are really important and which are not. Not all individual component identified should be regarded as significant aroma compounds since the aroma impact depends on the odor concentration and odor intensity. Some key odorants are found to be already present in unroasted cocoa. This may arise from compounds in the cocoa pulp or formed during the fermentation process. A recent report showed that cocoa pulps have a variety of flavor and aroma traits such as soursop, mango/rose, banana, jasmine, citrus and anona (Eskes et al., 2017). Chocolate made with cocoa beans with a banana pulp flavor showed

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a strong and persistent cooked banana/banana jam flavor. Unroasted Criollo cocoa beans contain compounds such as 2- and 3-methylbutanoic acid, 2-phenylethanol, 3-hydroxy-4,5-dimethyl-2(5H)-furanone, 2-methyl-3-(dithio)-furan and phenylacetic acid (Table 4.1) (Frauendorfer and Schieberle, 2008). During the fermentation and drying of Forastero cocoa beans, 39 volatile chemical compounds were identified (Rodriguez-Campos et al., 2011). The volatile compounds comprised of aldehydes and ketones (8), alcohols (9), esters (11), acids (10) and pyrazines (1). The ratio of aldehydes to amyl alcohols and acetates to amyl alcohols can be used as an indicator for the degree of fermentation. While many chemical compounds had been identified in the volatiles of roasted cocoa beans, the more important issue is the acceptance level of the cocoa beans (or final products, cocoa powder or chocolate) among the consumers such as taste/flavor. Several flavor attributes are used to describe flavors of cocoa such as cocoa/chocolate, bitter, sweet, astringent, sour/acid, fruity, bouquet/flowery and off-flavors such as hammy, smoky, musty and moldy. Good cocoa Table 4.1  Odor-Active Compounds in Fermented Criollo Cocoa UNROASTED CRIOLLO COCOA

ROASTED CRIOLLO COCOA

COMPOUNDS

ODOR QUALITY

COMPOUNDS

ODOR QUALITY

2- and 3-Methylbutanoic acid Acetic acid 2-Phenylethanol 3-Hydroxy-4,5-dimethyl2(5H)-furanone 2-Methoxyphenol Ethyl 2-methylbutanoate 2-Heptanol 2-Phenyl-ethyl acetate 2-Methyl-3(methyldithio)furan 4-Hydroxy-4,5-dimethyl2(5H)-furanone Phenylacetic acid

Rancid

2- and 3-Methylbutanal

Malty

Sour Flowery Seasoning-like

Phenylacetaldehyde 2-Phenylethanol 2-Heptanol

Honey-like Flowery Citrus-like

Smoky Fruity Citrus-like Flowery Cooked meat-like Caramel-like

2-Acetyl-1-pyrroline 2,3,5-Trimethylpyrazine 2-Ethyl-3,6-dimethylpyrazine 2,3-Diethyl-5-methylpyrazines 2-Methyl-3-(methyldithio)furan

Popcorn-like Earthy Earthy Earthy Cooked meat-like

2-Phenylethylacetate

Flowery

Sweet

2-Methoxyphenol

Smoky

Source: Adapted from Fraoundorfer, F. and P. Schieberle, 2008. “Changes in aroma compounds in Criollo cocoa beans during roasting,” Journal of Agricultural and Food Chemistry 56, 10244–10251.

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beans are characterized by a strong cocoa note, with low astringency and off-flavors. Bitterness and acidity should be present to balance the flavor. Additional good flavor notes are a bonus such as fruity and flowery notes. No individual compound can represent the single typical aroma of cocoa. From more than 600 different chemical compounds identified in cocoa beans, only about 25 compounds produce the typical good cocoa flavor (Schieberle, 2011). Individually, these compounds do not taste anything like cocoa but may smell like potato chips, cooked meat, peaches, raw beef fat, cooked cabbage, human sweat, earth, cucumber, honey and an improbable palate of other distinctly un-cocoa-like aromas. However, the correct combination is what produces the cocoa aroma we know. Acids are commonly found in cocoa volatiles which are formed during the fermentation process. Examples are such as acetic, propionic, isobutyric and isovaleric acids. These acids are associated with the occurrence of undesired odors such as rancidity, fat and cheese in cocoa, which can be described as off-odor or off-flavor. The intense bitter taste of cocoa is due to the presence of 4-methyl2-phenyl-2-pentenal and 5-methyl-2-phenyl-hexenal (Bonvehí, 2005). Linalool contributes to the flowery smell. Pyrazines are the main class of heterocyclic volatiles in cocoa and produce nutty, earthy, roasty and green aromas. About 80 pyrazines have been identified in cocoa volatiles (Afoakwa et al., 2008). The characteristic roasted cocoa smell is due to dimethyl pyrazine (DMP) and tetramethyl pyrazine (TMP). It was reported that the concentrations of DMP and tetramethyl pyrazine are proportional to pod storage period. Trimethyl pyrazine (TRMP) is biosynthesized during cocoa fermentation while other pyrazines are originated from the Maillard reaction during roasting. The concentration of individual pyrazines vary with the temperature and duration of roasting. The presence of the spicy descriptor may be related to the presence of dihydrocapsaicin, norhydrocapsaicin, homocapsaicin, carotenoids and flavonols, which are all of phenolic nature (Serra Bonvehí, 2005). A strong correlation has been found between bitter and spicy odors. The use of the spicy descriptor may also be associated with local terminology since the region has chilis of the genus Capsicum sp. called “chile chocolate” in Spanish, and panelists accustomed to this odor

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associate it with the powder of this chili (Vázquez-Ovando et  al., 2015). Phenol compounds can be an indicator of smoke contamination in cocoa beans. This contamination occurs mainly during the drying of the cocoa beans using an artificial dryer that uses wood-fired furnace. Uncontaminated cocoa samples should have the following maximum concentrations: phenol: 2 mg/kg, 3-methylphenol, 0.9 mg/ kg; 2,3-dimethylphenol: 0.55 mg/kg; 3-ethylphenol: 0.90 mg/kg; 4-ethylphenol: 0.70 mg/kg; and total phenols: 9.6 mg/kg. The cocoa powder produced from cocoa beans which had been exposed to 10 min of smoke showed a total phenol concentration of 12.7 mg/kg, while cocoa powder produced from cocoa beans exposed to 30 min of smoke showed a total phenol of 23.7 mg/kg (Bonvehí, 1998). The difficulty in correlating the instrumental data of flavor to the sensory profiles data was suggested by Lindinger et  al. (2009) to be due to two fundamental challenges. First, the different nature between the intensity scales for sensory and analytical measurement. Sensory attributes are usually evaluated within an arbitrary range (e.g., 0 to 10), while instrumental measurements result in signals that are not restricted in intensity. This leads to a very different relationship between the intensity of sensory v. analytical signals. Secondly, sensory scores are not proportional to concentration, and each odorant follows a specific non-linear sigmoid dose-response curve. However, instrumental signals are typically linear with concentration. An example given by the authors is when diluting coffee by defined factors; this will result in instrumental intensities reduced by the given factor leaving the signal intensity ratios unaltered. Diluting coffee makes the sensory profile less intense and can also result in an entirely different flavor profile. 4.2.2 Alkalization Effects

Alkalization or Dutching refers to the process where alkali solution such as potassium bicarbonate or sodium bicarbonate is added to cocoa nibs to modify the color and increase the pH. The cocoa powder made from this process is known as alkalized cocoa powder or Dutch cocoa powder. The name is derived from the fact that this method of treating cocoa was originated in the Netherlands. Alkalizing is commonly

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carried out to obtain a darker colored cocoa powder. Natural or nonalkalized cocoa powders are normally yellowish-brown in color and not the usual dark brown associated with cocoa. Parameters that can affect the outcome of the alkalization process include the type of alkali, the concentration of alkali solution, temperature, pressure, time and also the amount of air/oxygen. All this will affect the final color of the cocoa powder produced after roasting. Fermented cocoa beans are slightly acidic, with pH ranging from 5.0 to 5.6. Alkalization or the Dutch process neutralizes the normal cocoa acidity and raises the pH to 7–8. Since the Maillard reaction is affected by the pH of cocoa beans, the flavor compounds formed during the roasting of alkalized cocoa nibs are affected. Bonvehí (2005) reported that alkalized cocoa powder had fewer volatile compounds compared to roasted natural cocoa powder. Li et al. (2012) reported that alkalization of natural cocoa powder with NaOH reduced many compounds such as alcohols, acids, aldehydes, ketones and esters. However, d-limonene and furan compounds were found to increase with an increasing degree of alkalization. In terms of flavor, the roasted cocoa nib which undergoes the alkalization process will be less acidic. Alkalized cocoa nibs also has less astringency due to the further polymerization of flavonoid during the alkali reaction. The flavor aspect such as cocoa and bouquet are also enhanced. Besides changes in color and flavor, alkalization also reduces total polyphenol content, methylxanthines and amino acids. AndresLacueva et  al. (2008) reported a reduction of 67% epicatechin and 38% of catechin in cocoa powder after alkalization. Li et al. (2012) reported that alkalization affected the polyphenols, methylxanthines, amino acids and volatile compounds in commercial cocoa powder. Total polyphenols were seen to decrease with the increasing degree of alkalization. A heavy degree of alkalization greatly alters the components in cocoa powder, which leads to the unique flavor and color of the end products but the mechanism is still not well understood. The addition of 1% glucose during alkalization has led to the formation of compounds such as nonanal, ethanol, 2-propanal, 1-methoxy and 2(s)-acetoxysuccinic anhydride which were not detected in normal alkalization (Li et al., 2012). The same study also reported that the addition of glucose during alkalization retarded the reduction of acid while increasing the alcohol compounds. It has been suggested that

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incorporating the reduced sugar (glucose), more flavor compounds were produced via the formation of Schiff’s base and the Amadori rearrangement. 4.3 Methods for Analyzing Flavor Compounds

The methods used to determine flavor components depend on the extraction process, the aromatic intensity of cocoa and the chromatographic procedure applied. The aromatic extract must be representative of the product, avoiding the formation of an artifact, and suitably concentrated for chromatographic sensitivity (Bonvehí, 2005). Several methods commonly used include the following: • Flavor index using a spectrophotometer at 278 nm • Simultaneous extraction–distillation (SDE) techniques of Likens–Nickerson • Headspace solid-phase microextraction (HS-SPME) • Inline roasting hyphenated with gas chromatography–mass spectrometry Gas chromatography is used to determine the composition of the flavor compounds in all the methods except in the flavor index. The compound detection is determined by a flame ionization detector or mass spectrometer. The mass spectrometer is the better option since compounds can be identified using several existing libraries such as NIST and Wiley. 4.3.1 Flavor Index

This technique involves steam distillation of a cocoa sample (20 g) in 100 mL cold ultrapure water (resistance 18 mΩ cm–2). The condenser is maintained at –5°C and 15 mL of the fractional distillate is collected in 40 min. The solution obtained by steam distillation is filtered, and the optical density is measured in a 10-mm quartz cell using a spectrophotometer. The extinction value obtained from the UV spectra (210–290 nm) at 278 nm (maximum absorbance) is multiplied by the collected final volume to determine the value of flavor index and the acceptable value is higher than 45. An optimal flavor index was reported for roasting at 130°C for 16 min (heating-up period to reach

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130°C, 48 min) and 140°C for 10 min (heating-up period to reach 140°C, 58 min) with an addition of reducing sugars (Bonvehí, 2005). 4.3.2 Simultaneous Extraction–Distillation Techniques of Likens–Nickerson

The technique uses a specialized distillation apparatus, the Likens– Nickerson apparatus (Figure 4.1). The cocoa sample in water is steam distilled for several hours. In a smaller flask, 60 mL of a mixture of pentane/diethyl ether (2:1 v/v) is introduced. An internal standard, 4-ethylpyridine in methylene chloride is added to the sample. Boiling chips are added to both flasks. The sample flask is heated with a balloon heater, and the solvent flask is heated in an oil bath at 55°C. The vapors are condensed by means of a cold finger maintained at –5°C by a cryostat. After 90 min of extraction, about 55 mL of solvent containing the aroma compounds is collected. The extracts are then dried over 5 g of anhydrous Na 2SO4 and concentrated to about 1 mL in a Kuderna-Danish evaporator (Bonvehí, 2005).

Figure 4.1  Likens–Nickerson apparatus.

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The two most important parameters that influence aroma quality control in cocoa products are the pH adjustment before distillation and the collection of a definite volume of extract after distillation; higher sensorial aroma values were reported obtained for each of the responses at a lower pH range (1.5–3). The acid-extracted samples contained a more intense and chocolate-like aroma than the alkaline ones. The aroma concentrate can be further separated into several fractions by absorption chromatography on 3 g of silica gel 60. Several fractions can be obtained using solvents of increasing polarity, for example, Pentane, pentane/methylene chloride with different combination 4:1, 1:1, 1:2, pentane/ethyl ether and ethyl ether. The SDE technique has a disadvantage in that low-molecularweight aroma compounds cannot be detected or only detected in negligible amounts. Quantitation for short-chain aliphatic aldehydes and ketones is hard due to their volatility (e.g., hexanal and heptanal). These compounds may have volatilized from the samples before analysis and are also known to be affected by thermo degradation. Splitless injection in a gas chromatograph can favor the formation of a thermally induced artifact, for example, methyl furoate, methyl 3-hydroxyphenolacetate and methyl 2-(-methoxyphenylacetate) (Bonvehí, 2005). 4.3.3 Headspace Solid-Phase Microextraction (HS-SPME)

Headspace solid-phase microextraction (HS-SPME) offers an attractive alternative to the extraction of the volatile component in cocoa aroma by distillation or solvent extraction (Belardi and Pawliszyn, 1989). This technique is relatively cheap, simple, rapid and sensitive, and it does not use any solvent and is reproducible. The mild conditions used allow a good estimation of the aroma profile as perceived by the human sensory organs (nose and tongue) (Pini et al., 2004). The technique also eliminates problems associated with chemically and thermally unstable samples where the generation of artifacts can be problematic as in the case of cocoa and chocolate (Ducki et al., 2008). The procedure involves placing cocoa samples in a septum sealed glass vial and leaving them to condition for several minutes at the extraction temperature. A conditioned SPME fiber is inserted into the vial headspace and exposed for several minutes to absorb the

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volatiles. During the extraction procedure, the temperature of the vial is maintained at the extraction temperature. The extraction time is fixed for all samples. At the end of the extraction time, the volatiles absorbed onto the fiber are released into the gas chromatograph injection port for a specified time and temperature. The desorbed volatiles are splitlessly injected into the GC column and separated. The volatile compounds are commonly detected by a mass spectrometer detector and identified using an off-shelf library such as Wiley. During the volatile extraction in the vial, the sample can either be in a dry state or wet, that is, mixed with water or salt solution. The amount of compounds extracted by the fiber in a dry state is higher than under a wet condition. Increasing the ionic strength by adding brine to the sample resulted in better extraction than in plain water (Pini, 2004; Ducki et al., 2008). In a wet state, acids and alcohol compounds showed the largest difference. This is due to the high solubility of acid and alcohols in water, decreasing their presence in the volatile/ gaseous phase. Pyrazines also shows less absorption in plain water, but the absorption increases when the ionic strength is increased. However, in the presence of NaCl, those pyrazines are less soluble in water and thus increase their presence in the volatile fraction. The SPME fibers have a different coating; for example, 100 μm polydimethylsiloxane (PDMS), 65 μm polydimethylsiloxane/divinylbenzene coating (PDMS-DVB), 75 μm carboxen/polydimethylsiloxane (CAR-PDMS) and 50/30 μm divinylbenzene/carboxen on polydimethylsiloxane (DVB/CAR-PDMS). These fibers are durable and usually retain their performance for up to 100 analytical cycles. The non-polar PDMS fiber is suitable for extraction of non-polar analytes such as volatile flavor compounds but can also be applied to more polar compounds. Mixed fiber coatings, containing DVB or CAR, increase retention capacity due to a mutually potentiating effect on extraction and distribution of the stationary phase. Both PDMSDVB and CA-PDMS have been used for the extraction of a volatile low-molecular mass and polar analytes. The dual coated fiber DVB/ CAR-PDMS comprises a layer of PDMS-DVB over a layer of CARPDMS and is recommended for flavor and odor extraction (volatiles and semi-volatiles). Other coatins such as Carbowax (CWX) and polyacrylate (PA) have also been used in the study of pyrazines in cocoa (Pini et  al.,

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2004). Carbowax, a polar sorbent phase (polyglycol), has a higher affinity toward polar species such as alkylpyrazines compared to moderately polar polyacrylate and non-polar PDMS. Recently, a new microextraction technology known as SPME Arrow has been introduced. This apparatus was developed to overcome some of the drawbacks of SPME, such as the limited mechanical stability and the small-phase volume of the fibers (PALSystem, 2016; Kremser et al., 2016). The SPME Arrow is equipped with an arrow-shaped tip that encloses the sorption phase when it is closed and also helps to pierce the vial and injector septum. The SPME Arrow also has a larger sorption phase (30 mm × 250 μm) as compared to the conventional SPME fiber (10 mm × 100 μm). Due to the longer and thicker sorption phase, sensitivity is suggested to increase by 10 times. 4.3.4 Inline Roasting-Cooled Injection System Hyphenated with Gas Chromatography–Mass Spectrometry (ILR-CIS-GC-MS)

This method utilizes a very small amount of unroasted ground cocoa beans (0.06 g) packed into a microvial which is inserted into a quartz tube that can be inserted in a thermal desorption unit. All volatiles emitted during the roasting period are transferred to a cooled injection system which contains a liner with Tenax cooled at 1°C. After the roasting regime is complete, the cooled trap is flash heated (isothermal at 250°C, 5 min) and the volatiles are injected into a chromatographic column. Comparison between the inline roasting-cooled injection and headspace solid-phase microextraction showed that the amount of acetic acid is very much higher (17,742 ng/g vs. 496,915 ng/g in wellfermented Ghana cocoa beans) in the inline roasting method (Durme et al., 2016). Acetic acid concentrations were highly dominant in the aroma profiles of all cocoa samples. More pyrazines were found (1931 ng/g vs. 14,278 ng/g) in well-fermented Ghana cocoa beans compared to HS-SPME. Pyrazines were also detected in unfermented cocoa beans where in HS-SPME no pyrazine was found (Durme et  al., 2016). Overall, the total concentration was higher with an inline roasting-cooled injection. This can be explained by the fact that all gases emitted during roasting were retained in the cryogenic trap.

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When the roasted beans were evaluated, a significant portion of the formed volatiles were emitted into the air during a traditional roasting process. This is a promising technique for assessing the overall fermentation quality and aroma potential of unroasted cocoa beans. Data compared with headspace solid-phase microextraction (HS-SPME) on conventional roasted cocoa beans showed similar formation trends of important cocoa aroma markers as a function of fermentation quality. The aldehyde:amyl alcohol and tetramethylpyrazine:trimethyl pyrazine ratio are able to differentiate the level of the fermentation of cocoa beans. Continuous real-time online monitoring of the cocoa roasting process is very helpful for understanding the dynamics of flavor generation and could form the basis for future quality control measures such as to prevent over-roasting (Diab et al., 2014). Table 4.2 describes the advantages and limitations of the different methods of analyzing flavor as described above. 4.4 Risk of Contaminant Formation 4.4.1 Acrylamide

Acrylamide was evaluated by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) at its 64th meeting in 2005. Acrylamide is an important industrial chemical used since the mid1950s as a chemical intermediate in the production of polyacrylamide. Polyacrylamide is widely used in modern chemical technology for various purposes. These include usage as flocculants for sewage and wastewater treatment, as a coagulant for purifying drinking water, as a sealant for the construction of dams, tunnels and water reservoirs, as a soil stabilizer in roadways construction, as binders in the paper and pulp industry and as additives/adhesives/fixatives for manufacturing various industrial and cosmetic products (Besaratinia and Pfeifer, 2007). Several occupational and accidental exposures to acrylamide indicate that it is neurotoxic to humans. Experimental animal studies showed that acrylamide can induce reproductive, genotoxic and carcinogenic effects. Acrylamide is categorized as a human carcinogen (IARC, 1994) and the exposure to high levels of acrylamide may cause damage to the nervous system.

• Simple and inexpensive. • Concentration of flavor compounds. • Fractionation of flavor compounds. • Identification of flavor compounds possible with GC-MS.

• Relatively cheap, simple, rapid and sensitive. • No solvent is required. • Results are reproducible. • Good correlation of the aroma profile as perceived by human sensory organs. • Can be automated. • Identification of flavor compounds with GC-MS.

• Requires small unroasted cocoa samples (60 mg). • Can be automated. • No sample preparation. • Relatively short analytical time (< 1 hr). • Adequately reproducible.

Headspace solid-phase microextraction

Inline roasting-cooled injection system hyphenated with gas chromatography– mass spectrometry

ADVANTAGES

Flavor index Simultaneous extraction–distillation (SDE) (Likens–Nickerson)

METHOD

Table 4.2  Comparison of Methods to Analyze Flavor Compounds

• Aroma formation rates differ from traditional roasting.

• Flavor compounds trapped will be influenced by the type of fiber used. • Fiber can break easily. • Less formation of an artifact for chemically and thermally unstable samples.

• No information on individual flavor compounds. • Loss of low-molecular-weight aroma compounds. • Possible to form an artifact.

LIMITATIONS

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JECFA in their 64th and 72nd (FAO/WHO, 2005 and FAO/ WHO, 2010) meeting maintained the estimated average exposure to acrylamide was at 0.001 mg/kg bw per day for the general population and 0.004 mg/kg bw per day for high dietary consumers, respectively. The major food contributing to acrylamide in humans are potato fries (16–30%), potato chips (6–40%), coffee (13–30%), pastry and cookies (10–20%), bread and rolls/toast (10–30%) and other food items (less than 10%). Cocoa and cocoa products do not contribute very much to acrylamide intake. The presence of acrylamide in roasted cocoa beans is due to interactions between asparagines as one of the reactants and dicarbonyl compounds as a co-reactant in Strecker degradation (Maillard reaction) during roasting. Based on the GEMS database (WHO, 1994), the reported level of acrylamide in cocoa and cocoa products is between 9.38–1260 μg/kg. Table 4.3 is an extract from the GEMS database for acrylamide. A safe level of acrylamide in cocoa products has yet to be determined. According to the Food and Drug Administration, the safe limit of acrylamide in fries for human consumption is 0.077 ppm. Although the presence of acrylamide in food has not been shown to have an effect on human health, it has been shown to be carcinogenic in laboratory animals, thus making acrylamide a potential carcinogen to humans. Acrylamide was found in cocoa products such as cocoa powder (67 μg/kg) (Arisseto et al., 2008) and chocolate (23–537 ug/kg) Table 4.3  Concentration of Acrylamide in Food (2002 to 2004) FOOD GROUPS Bread and rolls Pastry and biscuits (cookies) Breakfast cereals Potato chips French fries Coffee decaffeinate Coffee extracts Cocoa products Green tea (“roasted”)

MEAN CONCENTRATION (μG/KG)

REPORTED MAXIMUM (μG/KG)

446 350 96 752 334 668 1100 220 306

3436 7834 1346 4080 5312 5399 4948 909 660

Source: Adapted from FAO/WHO. 2005. Joint FAO/WHO Expert Committee on Food Additives, 64th Meeting, Rome.

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(Ren et al., 2006). The average intake for the general population was estimated to be in the range of 0.3–2.0 μg/kg of body weight per day (FAO/WHO, 2005). Currently, no limit for acrylamide in food has been set, but the Centre for Science in the Public Interest (CSPI, 2003) suggested that the limit for acrylamide in fries should be set as 0.077 ppm as an acceptable interim level. This value is less than the amount of acrylamide reported in roasted cocoa beans. Acrylamide formation in cocoa-based products was found at 2 ppm and 826 ppm at the minimum and high level, respectively (FAO/WHO, 2005). 4.4.2 Biogenic Amine

Biogenic amines are low-molecular-weight organic bases with high biological activity present in plants as a free form (free bases), conjugated to small molecules such as phenolic acids or bound to highmolecular-weight compounds such as proteins or nucleic acids (Casal et al., 2004). The main biogenic amines found in cocoa and chocolate are 2-phenylethylamine, tyramine, tryptamine, serotonin, dopamine and histamine. 2-Phenylethylamine is an endogenous trace amine that occurs naturally in the brain of many mammalian species including humans. Tyramine, 2-phenylethylamine and tryptamine have been considered as the initiators of hypertension and dietary-induced migraines. Serotonin is an essential neurotransmitter and vasoconstrictor and plays an important role in the regulation of anger, appetite, body temperature, blood pressure, mood, sexuality and sleep. Dopamine is an endogenous catecholamine that determines many physiological functions, including behavior, nerve conduction, hormone synthesis and secretion, blood pressure and kidney function regulation. Bioactive amines are mainly formed in foods during microbial decarboxylation of free amino acids or by amination and transamination of ketones and aldehydes produced during Strecker degradation. They can also be formed during thermal processes as a result of the oxidative decarboxylation of corresponding amino acid precursors. Some authors have reported that the Strecker degradation is responsible for the formation of biogenic amines by way of thermal decarboxylation of amino acids in the presence of α-dicarbonyl compounds

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formed during the Maillard reaction or lipid peroxidation products. The Strecker degradation of asparagines results in the 3-aminopropionoamide formation. Serotonin may also form as a result of the transformation of its precursors (tryptophan and 5-hydroxytryptophan) at very high temperatures. Biogenic amines are not volatile and therefore do not contribute to the flavor of cocoa and cocoa products. However, there can be important effects in the human organism upon consumption (Aprotosoaie et al., 2016). Oracz and Nebesney (2014) reported that an important factor influencing the magnitude of changes in the content of biogenic amines is the cultivar of roasted cocoa beans. Roasted Trinitario beans from Papua New Guinea exhibited the highest total concentration of biogenic amines, ranging from 18.67 to 33.46 mg/kg ff-dw, followed by UAF hybrid beans from Ghana (10.69 to 23.67 mg/kg ff-dw), UAF hybrid beans from Ghana (10.69 to 23.67 mg/kg ff-dw), T × UAF hybrid beans from Cameroon and Indonesia (9.51 to 24.16 and 7.52 to 20.38 mg/kg ff-dw, respectively), Nacional beans from Ecuador (9.43 to 17.96 mg/kg ff-dw), and Trinitario beans from Venezuela (8.64 to 19.47 mg/kg ff-dw), while the roasted Forastero beans from Brazil showed the lowest amine content (4.42 to 8.03 mg/kg ff-dw). Studies indicated that the increase in the content of amines is much more pronounced during the roasting of fermented beans than in the case of non-fermented beans. This phenomenon can be directly related to the number of free amino acids, which in cocoa beans after fermentation is significantly higher than prior to fermentation (Rohsius et al., 2006). 4.5 Concluding Remarks

The generation of cocoa flavor compounds is the most important aspect of cocoa roasting. However, the flavors generated depend very much on the available flavor precursors in the cocoa beans after fermentation. While primary processing is responsible for producing the required flavor precursors, the roasting process will be an extension for releasing the coveted cocoa flavor. Roasting parameters, especially time and temperature, control the degree of roasting as well as the amount and type of flavor compounds formed. Even though the flavor

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formation pathway may not be fully understood, operators’ experience is equally important to ensure desired cocoa flavors are obtained. The study of cocoa flavor chemical compounds is an exciting and expanding research area. More sophisticated instruments are being utilized to study the actual flavor composition without cumbersome extraction procedures that may introduce artifacts. The need to understand each compound’s sensorial attributes make methods such as headspace solid-phase microextraction attached with a gas chromatograph–mass spectrometer and olfactory accessory (sniffing port) (HS-SPME GC-MS-O) an alternative to conventional methods.

References

Afoakwa, E.O., Paterson, A., Fowler, M., and Ryan, A. 2008. Flavor formation and character in cocoa and chocolate: A critical review. Critical Reviews in Food Science and Nutrition 48(9):840–857. Andres-Lacueva, C., Monagas, M., Khan, N., Izquierdo-Pulido, M., Urpi-Sarda, M., Permanyer, J., and Lamuela-Raventós, R.M. 2008. Flavanol and flavonol contents of cocoa powder products: Influence of the manufacturing process. Journal of Agricultural and Food Chemistry 56(9):3111–3117. Aprotosoaie, A.C., Luca, S.V., and Miron, A. 2016. Flavor chemistry of cocoa and cocoa products-an overview. Comprehensive Reviews in Food Science and Food Safety 15(1):73–91. Arisseto, A.P., de Figueiredo Toledo, M.C., Govaert, Y., van Loco, J., Fraselle, S., and Degroodt, J.M. 2008. A modified sample preparation for acrylamide determination in cocoa and coffee products. Food Analytical Methods 1(1):49–55. Bauermeister, P. 1981. Cocoa liquor roasting. The Manufacturing Confectioner 10:43–45. Belardi, R.P., and Pawliszyn, J.B. 1989. The application of chemically modified fused silica fibers in the extraction of organics from water matrix samples and their rapid transfer to capillary columns. Water Pollution Research Journal of Canada 24:179–191. Besaratinia, A., and Pfeifer, G.P. 2007. A review of mechanisms of acrylamide carcinogenicity. Carcinogenesis 28(3):519–528. Casal, S., Mendes, E., Alves, M.R., Alves, R.C., Beatriz, M., Oliveira, P.P., and Ferreira, M.A. 2004. Free and conjugated biogenic amines in green and unroasted coffee beans. Journal of Agricultural and Food Chemistry 52(20):6188–6192. CSPI. 2003. Acrylamide petition to the FDA. Center for Public Interest. https://cspinet.org/sites/default/files/attachment/acrylamide_petition. pdf (accessed on 5 December, 2017).

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de Brito, E.S., García, N.H.P., Gallão, M.I., Cortelazzo, A.L., Fevereiro, P.S., and Braga, M.R. 2001. Structural and chemical changes in cocoa (Theobroma cacao L.) during fermentation, drying and roasting. Journal of the Science of Food and Agriculture 81(2):281–288. Diab, J., Hertz-Schünemann, R., Streibel, T., and Zimmermann, R. 2014. Online measurement of volatile organic compounds released during roasting of cocoa beans. Food Research International 63:344–352. Ducki, S., Miralles-Garcia, J., Zumbé, A., Tornero, A., and Storey, D.M. 2008. Evaluation of solid-phase micro-extraction coupled to gas chromatography-mass spectrometry for the headspace analysis of volatile compounds in cocoa products. Talanta 74(5):1166–1174. Eskes, A.B., Rodriguez, A.A.C., Ahnert, D., Condori, D., Parizel, A., De Paula Durao, F., Matsigenkas, C., and Chunco growers in Peru. 2017. Advances in genetical and naturally induced variation for fine flavor and aromas in Theobroma cacao. Paper presented at the 2017 International Symposium on Cocoa Research (ISCR), Lima, Peru. FAO/WHO. 2005. Joint FAO/WHO Expert Committee on Food Additives. Sixty-Fourth Meeting, Rome. http://www.fao.org/3/a-at877e.pdf (accessed on 12 September, 2017). FAO/WHO. 2010. Joint FAO/WHO Expert Committee on Food Additives. Seventy-Second Meeting, Rome. http://fao.org/3/a-at868e.pdf (accessed on 12 September, 2017). Frauendorfer, F., and Schieberle, P. 2008. Changes in aroma compounds in Criollo cocoa beans during roasting. Journal of Agricultural and Food Chemistry 56(21):10244–10251. Heinzler, M., and Eichner, K. 1991. The role of amadori compounds during cocoa processing 2. Formation of aroma compounds under roasting conditions.   Zeitschrift für Lebensmittel-Untersuchung und Forschung 192(5):445–450. IARC. 1994. Monograph on the evaluation of carcinogenic risks to humans. International Agency for Research on Cancer. https://monographs.iarc. fr/iarc-monographs-on-the-evaluation-of-carcinogenic-risks-to-humans-61/ (accessed on 12 September, 2017). Ioannone, F., Di Mattia, C.D., De Gregorio, M., Sergi, M., Serafini, M., and Sacchetti, G. 2015. Flavanols, proanthocyanidins and antioxidant activity changes during cocoa (Theobroma cacao L.) roasting as affected by temperature and time of processing. Food Chemistry 174:256–262. Kamphius, H.J. 2009. Production and quality standards of cocoa mass, cocoa butter and cocoa powder. In: Industrial Chocolate Manufacture and Use (4th Edition), ed. S.T. Beckett, 121–139. Wiley-Blackwell. Keeney, P.G. 1972. Various interactions in chocolate flavour. Journal of the American Oil Chemists Society 49(10):567–572. Kleinert, J. 1994. Cleaning, roasting and winnowing. In: Industrial Chocolate Manufacture and Use (2nd Edition), ed. S.T. Beckett, 55–69. Blackie Academic and Professional. Kongor, J.E., Hinneh, M., de Walle, D.V., Afoakwa, E.O., Boeckx, P., and Dewettinck, K. 2016. Factors influencing quality variation in

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cocoa (Theobroma cacao) bean flavour profile – A review. Food Research International 82:44–52. Krähmer, A., Engel, A., Kadow, D., Ali, N., Umaharan, P., Kroh, L.W., and Schulz, H. 2015. Fast and neat-determination of biochemical quality parameters in cocoa using near infrared spectroscopy. Food Chemistry 181:152–159. Kremser, A., Jochmann, M.A., and Schmidt, T.C. 2016. PAL SPME Arrow – Evaluation of a novel solid-phase microextraction device for freely dissolved PAHs in water. Analytical and Bioanalytical Chemistry 408(3):943–952. Krysiak, W. 2011. Effects of convective and microwave roasting on the physicochemical properties of cocoa beans and cocoa butter extracted from this material. Grasas y Aceites 62(4):467–478. Li, Y., Feng, Y., Zhu, S., Luo, C., Ma, J., and Zhong, F. 2012. The effect of alkalization on the bioactive and flavour related components in commercial cocoa powder. Journal of Food Composition and Analysis 25(1):17–23. Lindinger, C., Yeretzian, C., and Blank, I. 2009. When machine tastes coffee: Successful prediction of coffee sensory profiles by instrumental methods based on on-line PTR-MS. Chimia International Journal for Chemistry 63(5):292. Martins, S.I.F.S., Jorgen, W.M.F., and van Boekel, M.A.J.S. 2001. A review of Maillard reaction in food and implication to kinetic modeling. Trends in Food Science and Technology 11:364–373. Oracz, J., and Nebesny, E. 2014. Influence of roasting conditions on the biogenic amine content in cocoa beans of different Theobroma cacao cultivars. Food Research International 55:1–10. PALSystem. 2016. PAL SPME Arrow. The Better SPME. https://www. palsystem.com/fileadmin/public/docs/Downloads/Brochures/PAL_ SPME_Arrow:Broschuere+Rev6_Spread.pdf (accessed on 5 December, 2017). Pini, G.F., de Brito, E.S., Farcia, N.H.P., Valente, A.L.P., and Augusto, F. 2004. A headspace solid phase microextraction (HS-SPME) method for the chromatographic determination of alkylpyrazines in cocoa samples. Journal of Brazilian Chemical Society 15(2):267–271. Ren, Y., Zhang, Y., Jiao, J., Cai, Z., and Zhang, Y. 2006. Sensitive isotope dilution liquid chromatography/electrospray ionization tandem mass spectrometry method for the determination of acrylamide in chocolate. Food Additives and Contaminants 23(3):228–236. Rodriguez-Campos, J., Escalona-Buendía, H.B., Orozco-Avila, I., LugoCervantes, E., and Jaramillo-Flores, M.E. 2011. Dynamics of volatile and non-volatile compounds in cocoa (Theobroma cacao L.) during fermentation and drying processes using principal components analysis. Food Research International 44(1):250–258. Rohsius, C., Matissek, R., and Lieberei, R. 2006. Free amino acids amounts in raw cocoa from different origins. European Food Research and Technology 222(3–4):432–438.

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Sacchetti, G., Ioannone, F., De Gregorio, M., Di Mattia, C., Serafini, M., and Mastrocola, D. 2016. Non enzymatic browning during cocoa roasting as affected by processing time and temperature. Journal of Food Engineering 169:44–52. Saltini, R., Akkerman, R., and Frosch, S. 2013. Optimizing chocolate production through traceability: A review of the influence of farming practices on cocoa bean quality. Food Control 29(1):167–187. Schieberle, P. 2011. What’s really in that luscious chocolate aroma? Paper presented at the 242nd National Meeting and Exposition of the American Chemical Society, 28 August–1 September, Denver, CO. Serra Bonvehí, J. 2005. Investigation of aromatic compounds in roasted cocoa powder. European Food Research and Technology 221(1–2):19–29. Serra Bonvehí, J., and Ventura Coll, F. 1998. Evaluation of smoky taste in cocoa powder. Journal of Agricultural and Food Chemistry 46(2):620–624. Summa, C., Raposo, F.C., McCourt, J., Scalzo, R.L., Wagner, K.H., Elmadfa, I., and Anklam, E. 2006. Effect of roasting on the radical scavenging activity of cocoa beans. European Food Research and Technology 222(3–4):368–375. Suzannah, S. 2004. d-fructose addition during Malaysian cocoa nibs roasting. Malaysian Cocoa Journal 1:50–66. Van Durme, J., Ingels, I., and De Winne, A. 2016. Inline roasting hypernated with gas chromatography-mass spectrometry as an innovative approach for assessment of cocoa fermentation quality and aroma formation potential. Food Chemistry 205:66–72. Vázquez-Ovando, A., Chacón-Martínez, L., Betancur-Ancona, D., EscalonaBuendía, H., and Salvador-Figueroa, M. 2015. Sensory descriptors of cocoa beans from cultivated trees of Soconusco, Chiapas, Mexico. Food Science and Technology 35(2):285–290. Voigt, J., Textoris-Taube, K., and Wöstemeyer, J. 2018. pH-dependency of the proteolytic formation of cocoa and nutty-specific aroma precursors. Food Chemistry 255:209–215. WHO. 1994. Global environment monitoring system – Food contamination monitoring and assessment programme (GEMS/food). World Health Organization. http://apps.who.int/iris/handle/10665/58537 (accessed on 17 September, 2017). Ziegleder, G. 2009. Flavour development in cocoa and chocolate. In: Industrial Chocolate Manufacture and Use, ed. S.T. Beckett, 169–191. UK: Wiley-Blackwell.

5 The G r ad in g and Q ualit y of D ried C ocoa B e ans DA R I N A S H R A M S U K H A Contents

5.1 Introduction 90 5.2 Quality Defined and Its Importance along the Cocoa Value Chain 91 5.2.1 Genetic Composition of Cocoa and Its Links to Flavor Development 92 5.2.2 Pre-Harvest Conditions Effects on Cocoa Quality 94 5.2.3 Harvesting, Pod Breaking and Wet Bean Extraction 95 5.2.4 Expressing Genetic Flavor Potential by Optimal Postharvest Processing 96 5.2.4.1  The Importance of Fermentation on Flavor 96 5.2.4.2  The Importance of Drying on Flavor 98 5.2.4.3  Storage Considerations for Cocoa Beans 99 5.3 Food Safety Considerations in Cocoa 100 5.3.1 Physical Risks 102 5.3.2 Chemical Risks 103 5.3.3 Microbial Risks 106 5.4 Sampling for Cocoa Quality Grading 107 5.4.1 Sample Passport Data 108 5.5 Physical Assessments 109 5.5.1 Moisture Content 110 5.5.2 Bean Count and Individual Bean Weight 110 5.5.3 Cut Tests 111 5.5.3.1  Aroma Assessment 115 5.6 Sensory Quality 115 5.6.1 Tasting Area and Layout 116 5.6.2 Panelist Training 117 5.6.2.1  Basic Tastes Identification at Normal and Threshold Levels with Aroma Identification 118 89

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5.6.2.2  Flavor Descriptors 119 5.6.3 Tasting Design, Sample Randomization and Presentation 123 5.6.4 Sensory Evaluation of Cocoa Liquors 123 5.6.5 Sensory Evaluation of Chocolates 125 5.6.6 Panelist Calibration, Interpreting and Visualizing Sensory Results 126 5.7 Elements of a Harmonized Grading and Quality Management System of Cocoa 127 5.8 Traceability 130 5.9 Concluding Remarks 132 References 132 5.1 Introduction

The International Cocoa Organization (ICCO) hosted the First World Cocoa Conference in Abidjan, Côte d’Ivoire in November, 2012. The aim of this conference was to build on the previous two successful roundtable discussions on a sustainable cocoa economy and provide a roadmap toward achieving a sustainable world cocoa economy. Some of the strategic challenges facing the cocoa value chain were outlined with recommended actions for addressing them and the responsibilities of the stakeholders in the cocoa sector at national and regional and international levels. This was encapsulated in the “Abidjan Declaration” (ICCO, 2012). Arising from this were a number of “Global Cocoa Agenda Actions,” one key action identified was to “Improve cocoa quality by better communication of industry needs, postharvest processing and quality assessment.” Realizing the Global Cocoa Agenda relies on secure partnerships built at all levels of the cocoa supply chain between origin country governments and local authorities with international agencies. All these players must now work together to address the complex challenge of achieving a sustainable cocoa economy as outlined in the Global Cocoa Agenda. Taking cues from what has happened in the specialty coffee sector and in other commodities, the approaches taken now must allow cocoa growing communities to sustainably improve their livelihoods and well-being, while producing cocoa in the quantity and quality needed by the cocoa and chocolate industry to manufacture products

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for satisfying the requirements of a new generation of very informed consumers. With this in mind, we must consider that each cocoa bean has a genetic flavor potential that is either expressed or depressed as it moves along the cocoa processing chain. Best practices express this genetic potential, while poor practices depress or reduce the expression of full genetic potential. Having a clear understanding of what this potential is, being able to communicate this information and, most importantly, being able to assess for these attributes are fundamental understandings that have a direct impact on final cocoa bean quality; this is at the core of this chapter. 5.2 Quality Defined and Its Importance along the Cocoa Value Chain

The evolution of sensory evaluation as a science and its critical role in re-defining cocoa quality is now re-shaping how to examine cocoa as a food. Indeed, the use of physical bean evaluation coupled with sensory evaluation as a tool to drive improvements in the continuum of activities that occur across the cocoa value chain are key elements in developing niche marketing opportunities for high-quality cocoa. Drawing from the revised “Cocoa Beans: Chocolate and Cocoa Industry Quality Requirements” (CAOBISCO/ECA/FCC, 2015), “cocoa quality” is used in its broadest sense to include not just the all-important aspects of flavor and food safety, but also the physical characteristics that have a direct bearing on manufacturing performance, and aspects such as traceability, geographical indications and certification to indicate the sustainability of the production methods. According to this revised definition, aspects or specifications of quality in cocoa now include: • • • • • • • •

Flavor Food safety and wholesomeness Physical characteristics Consistency Yield of edible material Cocoa butter characteristics Color potential Traceability, geographical indicators and certification

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These are the key physical, chemical, microbial and sensory criteria affecting a manufacturer’s assessment of the “value” of a particular parcel of beans and the price that it ultimately fetches on the international market. In the United Nations Food and Agricultural Organization (FAO) “Model Ordinance of the International Cocoa Standards” (BCCCA, 1996), cocoa of merchantable quality is defined as being: • Fermented, thoroughly dry, free from smoky beans, free from abnormal or foreign odors and free from any evidence of adulteration • Reasonably uniform in size, reasonably free from broken beans, fragments and pieces of shell, and virtually free from foreign matter When these definitions are applied to cocoa, no matter what the genetic origin, according to Rohan and Stewart (1966), the flavor and aroma potential of each marketed cocoa variety can only be expressed by a continuum of factors that include: • The genetic composition of the bean (genetic flavor potential of different varieties) • Pre-harvest conditions affecting pest and disease incidence • Postharvest processing (fermentation and drying) • During manufacturing (roasting, milling/grinding), product formulation and conching (for chocolate) 5.2.1 Genetic Composition of Cocoa and Its Links to Flavor Development

Motomayor et al. (2008), in a study of cocoa germplasm from Central and South America, proposed a new classification of cocoa germplasm with 10 genetic clusters that supports the palaeoarches hypothesis of species diversification viz. Amelonado, Contamana, Criollo, Curaray, Guiana, Iquitos, Marañon, Nacional, Nanay and Purus. Each of these have different characteristics and have different origin locations, as shown in Figure 5.1, linked to areas of forest that have been isolated mainly by major tributaries flowing into the Amazon River. This is in contrast to the current world cocoa market distinction of two genetic groups and one hybrid group traditionally recognized, that is, Criollo, Forastero and

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Figure 5.1  The approximate location of a new classification of cacao germplasm with 10 genetic clusters that supports the palaeoarches hypothesis of species diversification. (From Motamayor et al., 2008.)

Trinitario, with just two broad categories of cocoa that are traded: “bulk” or “ordinary” and “fine or flavor” cocoa beans (ICCO, 2017a). The first consideration in the definition of cocoa quality from CAOBISCO/ECA/FCC (2015) refers to the flavor. This is a key criterion of quality for manufacturers of cocoa products and includes both the intensity of the cocoa or chocolate flavor (typical in many traded “bulk” cocoas) together with ancillary flavor notes (dominant in many traded “fine or flavor” cocoas) and the absence of flavor defects regardless of traded cocoa type. It should be noted, according to the ICCO, the main difference between bulk or ordinary cocoa and fine or flavor cocoa is primarily due to the flavor but can also include other quality factors such as variety, origin and price. Key ancillary flavors that are sought after include fruit (fresh and browned mature fruits), floral, herbal, and wood notes, nut and caramel type notes, as well as rich and balanced chocolate bases (ICCO, 2017a). Approximately 95% of the cocoa produced globally is considered bulk or ordinary cocoa beans and are produced mainly in West Africa and come from what are considered Forastero trees while fine or flavor cocoa beans are produced from Criollo or Trinitario cocoa tree varieties. There are, however, known exceptions to this generalization. “Nacional” trees in Ecuador, considered to be Forastero type trees,

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produce fine or flavor cocoa. On the other hand, cocoa beans from Cameroon, produced by Trinitario type trees and whose cocoa powder has a distinct and sought after red color, have, so far, been classified as bulk cocoa beans (ICCO, 2017a). These distinctions between “bulk” or “ordinary” and “fine or flavor” cocoa beans and their respective producers (either exclusively or partially) as well as the narrow genetic classifications being used (ICCO, 2017b) are being revisited by the ICCO with a broad stakeholder input to be more holistic in their considerations. This re-examination is considering, among other factors, the work of Motomayor et al. (2008) as it provides a better understanding of population differentiation within the species and facilitates enhanced management and utilization according to flavor potential. Current work by Ali et al. (2017, 2015) is looking at the fermentation requirements, flavor and other quality attributes of six of the ten genetic clusters identified by Motomayor et  al. (2008) with a view toward fermentation manipulation and optimization allowing the exploitation of the inherent diversity in pulp quality, flavor and bean chemical characteristics toward genetic branding. 5.2.2 Pre-Harvest Conditions Effects on Cocoa Quality

In addition to genetic factors, pre-harvest conditions have a significant impact on final cocoa bean quality and include considerations of farm location, soil type, nutrient status and fertility, land tenure, cultivation system and agronomic practices. Although the cocoa tree is adapted to shade conditions with high humidity, high rainfall and temperatures in the range of 20–33°C (68–91°F). The annual rainfall total of major producing countries ranges from 1300 to 2800 mm (51–110 inches) (Butler/Umaharan, 2004; Mossu, 1992 and Wood, 1985a) and may be evenly distributed through the year or with one or two distinct dry seasons, when monthly totals are less than 100 mm (Ca 4 inches) (Wood, 1985a). Climates with less than 1200 mm (51 inches) per year are not suitable, and those with more than 3000 mm (110 inches) result in severe disease problems (Wood, 1985a). Rainfall, ambient temperature and light conditions also have impacts on the progress of fermentation, drying method and efficiency, as well as storage and resulting bean quality (CAOBISCO/ECA/FCC, 2015).

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According to CAOBISCO/ECA/FCC (2015), Wood (1985b) and Butler et al. (2004), during pod development, some physical characteristics of cocoa beans are influenced by the climate which, in addition to edaphic considerations, includes rainfall, ambient temperature and light conditions. Cocoa fruits that develop during dry conditions or in less fertile soil tend to contain smaller beans than fruits that develop during the wet season or on more fertile soil. Butterfat content and hardness are also influenced by rainfall and temperature. Studies by Lehrian et al. (1980) highlighted that cocoa butter from beans which developed during cooler months showed a higher proportion of unsaturated fatty acids and therefore were softer compared to beans developed in warmer periods. The impact of land tenure on cocoa production, productivity and land use has been surveyed and assessed, mainly in West Africa as reported by USAID/WCF/Cocobod (2015, 2017) and Gbadeboa and Oluwoyeb (2015), where 73% of world cocoa output in 2015/2016 was produced (ICCO, 2016). These reports indicate that when land tenure is not secure, cocoa farmers are less inclined to make financial, infrastructural and agronomic investments to improve land access, cocoa production and productivity. As a result, production, productivity and cocoa quality declines due to a higher incidence of pest and disease problems, as well as a lack of any Integrated Crop and Pest Management (ICPM) systems to achieve sustainable good yields (CAOBISCO/ECA/FCC, 2015). Non-sustainable production systems such as practicing clear felling and “slash and burn” with unsuitable temporary and permanent shade trees, as well as using unsuitable planting materials at inefficient planting densities, compound these production issues with further negative impact on productivity and quality (Wood, 1985b). 5.2.3 Harvesting, Pod Breaking and Wet Bean Extraction

Apart from agronomic and agro-ecological considerations, the quality of wet cocoa beans going into fermentation can directly impact fermentation, expression of flavor potential and ultimately final bean quality. Full details of these factors to consider are presented in CAOBISCO/ECA/FCC (2015) and as a summary of key considerations, only fully mature, ripe, un-diseased fruits should be harvested

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with a sorting stage to remove any unwanted materials and beans from immature, overripe or damaged/diseased pods, which can impact on physical, chemical, microbial and flavor quality attributes. The harvesting action should also not damage the tree and flower cushions as this reduces future yield from the trees. Also, fruits wounded during harvesting should not be stored for longer than one day before starting fermentation, as it can be a potential source of ochratoxin “A” contamination. Beans from immature fruits do not separate easily from each other and the placenta and therefore are often hard to remove. The pulp on beans from these immature fruits will not ferment properly due to a higher pectin content and less free sugars. On the other hand, overripe fruits tend to have beans that are dry and may have already germinated. These beans would have a damaged seed coat from germination and the emerging radicle that are usually lost during drying and storage creating a ready entry point for molds, insects and other contaminants into the beans (CAOBISCO/ECA/FCC, 2015). Fruit breaking and wet bean extraction, if not done properly, can also have a negative impact on physical, chemical, microbial and flavor quality attributes if beans are cut or otherwise damaged during opening. It is preferable to open fruits by striking them with a wooden baton or a mechanical device designed to minimize damage to the beans, rather than a machete which may cut the beans or even cause injury to the farmers’ hands. These actions will result in a negative impact on fermentation, which may later facilitate mold and insect infestations (CAOBISCO/ECA/FCC, 2015). 5.2.4 Expressing Genetic Flavor Potential by Optimal Postharvest Processing

In summary, the interconnectivity of all the activities along the cocoa value chain using a Hazard Analysis Critical Point (HACCP) approach is emphasized in Figure 5.2. These represent critical control points affecting physical, chemical, microbial bean quality and expression of genetic flavor potential. 5.2.4.1 The Importance of Fermentation on Flavor  Beans inside the

unopened cocoa fruit are sterile with astringent and bitter tasting seeds when fresh due to unexpressed intrinsic aroma precursors and

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Figure 5.2  Critical control points for cocoa postharvest processing. (From Sukha, 2017b.)

the high content of anthocyanins and other phenolics (Ziegleder/ Biehl, 1988; Jinap et al., 2005). Opening the fruits and extracting the beans exposes the pectinaceous and sweet pulp surrounding the beans to many sources of inoculation which start a microbial succession of yeasts, acetic acid bacteria and lactic acid bacteria that influences good processing and quality (Ostovar/Keeney, 1973; Schwan/Fleet, 2014; Sandhya et al., 2016). These microorganisms act on sugars and acids in the cocoa pulp, triggering intense enzymatic activity that elevates bean temperatures up to 50–52°C and produce ethanol, lactic acid and acetic acid. The acetic acid diffuses through the differentially permeable seed coat into the seed tissue causing seed death and the production of flavor precursors by degrading the polyphenols, storage proteins and carbohydrates into peptides, free amino acids and reducing sugars thereby “unlocking” the genetic flavor potential that resides within each bean. Over-fermentation arises if fermentation is allowed to continue after this acetic acid stage leading to a rise in bacilli and filamentous fungi that can cause off-flavors (Ostovar/Keeney, 1973; Ziegleder/Biehl, 1988; Schwan, 1998; Schwan/Wheals, 2004; Andersson et al., 2006; Rohsius et al., 2006; Lagunes Gálvez et al., 2007; Nielsen et al., 2007; Afoakwa et al., 2008; Camu et al., 2008;

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De Bruyne et  al., 2008; Kostinek et  al., 2008; Kadow et  al., 2013; Badrie et al., 2015). Additional studies on the impact of exogenous factors on cocoa bean flavors by Kadow et al. (2013) highlighted quantitative and qualitative differences in the aromatic profile of fruit pulp from different cocoa cultivars. This indicates that further to the endogenous formation of flavor and aroma precursors from fermentation, there may be some exogenous influence of the pulp directly on aroma and flavor in that aroma components present in the fruit pulp can migrate into the cotyledon tissue during ripening in addition to those derived from fermentation. Complimentary studies by Eskes et al. (2007, 2012) and Ali et al. (2014) discuss the direct permeation of aroma components from the pulp into the seed tissue during fermentation by using the addition of extra pulp from other fruits as an indicator to determine if the added pulp affects final flavor quality which may be retained during drying. In looking at the impact of the pollen donor on flavor, Sukha et al. (2017) failed to detect direct xenia effects for most of the important flavor attributes, that is, cocoa flavor, acidity, fruitiness and floral flavor which agrees with the preliminary work of Clapperton et al. (1994a and 1994b) and Lockwood and Eskes (1996) implying that the flavor quality of cocoa beans is determined principally by the genotype of the female parent. 5.2.4.2  The Importance of Drying on Flavor  After fermentation, cocoa

beans contain about 60% moisture content (wet basis) which must be reduced to between 6–7% for safe storage and transportation without becoming contaminated by molds, Salmonella bacteria, polycyclic aromatic hydrocarbons (PAHs) and other contaminants (CAOBISCO/ ECA/FCC, 2015). Other objectives of drying include oxidative chemical reactions that reduce the astringency and bitterness of the bean and the development of the typical brown color associated with well-fermented and dried cocoa beans (Wood, 1961; Wood, 1985c; Hii et  al., 2008; Fagunwa et  al., 2009). Climate and production capacity and other resources often dictate the drying method used; however, sun drying is the most widely practiced method due to the simplicity and use of natural energy (Bravo, 1974; McDonald/Lopez, 1981; Bonaparte et al., 1998; Hii et al., 2006). This method has some drawbacks as it is labor intensive, weather dependent, with sometimes

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negative effects on quality, and requires a large area to locate drying floors. In areas where rainy weather is prevalent during peak cocoa crop times and/or when production capacity outstrips available drying capacity or space, artificial drying systems are sometimes used to shorten drying time, increase throughput efficiency and increase the rate of moisture removal (Wood, 1985c; Faborode et  al., 1995 and Ndukwu, 2009). Regardless of the drying method used, the final moisture content of the bean and the drying rate of this moisture content has direct implications on physical, chemical, sensory and food safe quality of the dried beans (Jinap, 1994; Jinap et al., 1994; Faborode, Favier/Ajayi, 1995; Schwan/Wheals, 2004; Rodriguez-Campos et al., 2012). The rate of drying depends on two factors: the transfer of heat into the bean and the movement of water vapor from the bean to the surrounding air (Wood, 1985c; Wan Daud et al., 1996; Hii, Law/Cloke, 2008; Hii et al., 2009; Chinenye et al., 2010). In artificial drying, extra care should be taken to have a relatively slow drying rate with air temperatures not exceeding 40°C until the moisture content of the beans is below 20% (Clapperton et al., 1994a). Final moisture content below 5% can result in brittle beans, while moisture contents of more than 8% can increase the risk of mold growth (Wood, 1985c; Schwan/Wheals, 2004). Slow drying can sometimes result in over-fermentation of the beans and mold growth outside and inside the bean, which can contribute to strong putrid, rancid and hammy off-flavors (Schwan/Wheals, 2004; Hii et  al., 2006). Too rapid drying can result in acidic beans with shriveling and/or case hardening of the shells (Jinap, 1994; Jinap, Thien/Yap, 1994; Augber et al., 1999). Smoke contamination, on the other hand, arises from direct-fired artificial dryers without heat exchangers that use either liquid fuel (diesel or kerosene) or wood (Lowor et al., 2012). 5.2.4.3  Storage Considerations for Cocoa Beans  Storage in the tropics

poses a unique set of challenges related for preventing re-humidification, insect infestation and contamination of the beans, as well as providing appropriate ventilation. In the context of physical, chemical, sensory and food safety attributes, storage should be in an area that is clean with appropriate temperature and humidity control, free from insect and rodent pests (Wood, 1985c; CAOBISCO/ECA/FCC, 2015).

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Ideally, the floor of the warehouse should be made from cement or from non-flammable materials without cracks and crevices where insects can hide. The floor level of the warehouse should be higher than the surrounding areas to prevent flooding and to allow water to flow away (ICCO, 2015). Storage periods in the tropics usually do not exceed three months unless special precautions are taken such as temperature control at 20°C and humidity control with dehumidifiers (CAOBISCO/ECA/FCC, 2015). Cleaning the fermented and dried beans and checking the moisture content prior to storage is recommended and has an impact on factors associated with consistency and purity while secondary mold growth from re-humidification caused by moisture contents above 8% leads to fat degradation with a rise in free fatty acids leading to negative flavor and other quality effects later on during chocolate processing (Wood, 1985c; CAOBISCO/ECA/FCC, 2015). Having a systematic warehouse inspection program is also a critical element in identifying and minimizing risks during storage (CMAA, 2015a). Traceability systems that facilitate the niche marketing of beans from a particular region rely on the identification of cocoa beans according to lots, either at the farm level or in larger off-farm warehouses. Additionally, to prevent problems from secondary infestation and allergenic cross-contamination, any bags used to store the beans should be labeled to indicate that the beans are suitable for food contact use; clean and sufficiently strong and properly sewn or sealed to withstand transport and storage and discourage pest infestation. Where cocoa production overlaps with allergenic crops (such as peanuts or sesame), new or cocoa-dedicated bags must be used to avoid cross-contamination and allergenic food safety concerns (Wood, 1985c; CAOBISCO/ECA/FCC, 2015). 5.3 Food Safety Considerations in Cocoa

It is essential that cocoa and chocolate products, in common with all other food products, should be safe to eat and wholesome. This is the second main consideration after flavor in the definition of “cocoa quality” taken from the revised “Cocoa Beans: Chocolate and Cocoa Industry Quality Requirements” (CAOBISCO/ECA/FCC, 2015). In viewing cocoa as a food item, the basic food safety concept is that

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it will not harm the final consumer so long as intended use guidelines are followed when it is prepared/processed or eaten. Conversely, according to the “Food Safety Management Systems – Requirements for Any Organization in the Food Chain” (ISO, 2005), any food is potentially harmful whenever it has been exposed to hazardous agents, and intended use guidelines have not been followed. This responsibility for food safety is therefore shared by everyone involved in the cocoa value chain from production to consumption and involves growers, processors, regulators, distributors, chocolate makers, retailers and consumers. This so-called “chain of custody” is critical to cocoa quality control and traceability systems for the sale of cocoa beans with the objective of reducing physical, chemical and microbial risks ensuring that all national and international legislative requirements along the cocoa value chain at point of entry and in the market place are met (CAOBISCO/ECA/FCC, 2015). It follows then, that all chocolate ingredients, including cocoa beans, should not contain any impurities which could be present in the finished foods and prove injurious to the health of the consumer. Toward this end, a number of organizations have been set up to establish regulations, standards and guidelines for food safety management to ensure that hazards at any stage of the supply chain, from the farm to the consumer, can be identified and controlled. Some of these main international organizations involved in food safety considerations with some general or special/dedicated guidelines quality control of cocoa beans and chocolate products are presented below together with their web address to get more details of specific quality guidelines, regulations or specifications related to cocoa beans and chocolate. • The Codex Alimentarius Commission [http://www.fao.org/ fao-who-codexalimentarius/en/] • International Organization for Standardization [https:// www.iso.org/home.html] • The Food Safety and Inspection Service (FSIS) of the U.S. Department of Agriculture [https://www.fsis.usda.gov/wps/ portal/fsis/home] • The U.S. Food and Drug Administration (FDA) through its Center for Food Safety and Applied Nutrition (CFSAN)

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[htt ps://www.f da.go v/AboutFDA/CentersOffices/ OfficeofFoods/CFSAN/ContactCFSAN/default.htm] Centers for Disease Control and Prevention (CDC) [https:// www.cdc.gov/] Canadian Food Inspection Agency (CFIA) [http://www. inspection.gc.ca/eng/1297964599443/1297965645317] Food Standards Agency (FSA) [https://www.food.gov.uk/] EC Regulation 178/2002 and its amendments in Europe establishing the European Food Safety Authority (EFSA) [https://www.efsa.europa.eu/] Rapid Alert System for Food and Feed (RASFF) [https:// ec.europa.eu/food/safety/rasff_en] Association of Chocolate, Biscuits and Confectionery (CAOBISCO) [http://caobisco.eu/] Syndicat du Chocolat [http://www.syndicatduchocolat.fr/]

According to CAOBISCO/ECA/FCC (2015), some principal food safety concerns in cocoa beans under physical, chemical and microbial risks include allergens, dioxins and Polychlorinated biphenyls (PCBs), bacteria, foreign matter, heavy metals, infestation, mineral oil hydrocarbons (PAHs), mycotoxins including ochratoxin A (OTA) and pesticide residues. A summary considering the physical, chemical and microbial risks is discussed further. 5.3.1 Physical Risks

Contamination of cocoa beans with foreign matter should be avoided at all stages of the supply chain from fermentation through drying and subsequent handling. Sorting beans before storage or as part of the final bagging process before shipping to remove any foreign matter such as sticks/twigs, stones, leaves and bits of metal, as well as defective beans including those that are flat, slaty, shriveled, black, moldy, germinated, insect-damaged, small and/or fused together, minimizes some of the physical risks that affects the wholesomeness of the product. Additionally, these may also affect the flavor, cause damage to plant and machinery and reduce the yield of edible material (Wood, 1985c; CAOBISCO/ECA/FCC, 2015; CMAA, 2015b). Although insect infestation is being considered under physical risks, it also poses microbial and chemical risks as well. Prevention

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remains the best option, but it is possible that infestation will occur, particularly at origin and in tropical consuming regions, by one or more of several species of the following insects and other pest species including the tropical warehouse moth (Ephestia cautella), Indian meal moth (Plodia interpunctella), dried fruit beetle (Caropophilus spp.), foreign grain beetle (Ahasverus advena), red-rust grain beetle (Cryptolestes ferrineus), the tobacco beetle (Lasiodema serricorne) and the coffee bean weevil (Araecerus fascinulatus). Care and clean surroundings at all stages of transport and storage from farm to export insures that infestation is kept to a minimum (Wood, 1985c; CAOBISCO/ECA/ FCC, 2015; CMAA, 2015b). 5.3.2 Chemical Risks

Chemical contamination can take the form of persistent environmental pollutants (POPs) that mostly occur as by-products of industrial processes. These are organic compounds (found in herbicides, pesticides, insecticides, etc.) that are resistant to environmental degradation and bio-accumulate with potential adverse impacts on human health and the environment (EPA-Ghana, 2007). However, the main chemical risks arise from the fumigation of beans and the use of chemicals during cocoa production. Effective pre-shipment fumigation at origin by a reputable agent will control insects, rodents and other pests. However, any residue from chemical fumigation can pose a risk and should not exceed the maximum residue limits indicated for the pesticides used as prescribed by the Codex Committee on Pesticide Residues (CCPR). According to prescribed guidelines, the choice of pesticides and the technique of their application should be made/performed with great care to avoid incurring the risk of tainting or the addition of toxic residues to the cocoa (Wood, 1985c; CAOBISCO/ ECA/FCC, 2015). Various alternatives to methyl bromide (such as phosphine) and non-chemical fumigation alternatives are now being considered to remove or reduce chemical risks from fumigation. Non-chemical fumigation alternatives include the removal of oxygen (fumigation with carbon dioxide) in order to asphyxiate the pests, to ozone fumigation, heat treatment or putting the cocoa beans in refrigerated containers and reducing the temperature to well below freezing

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point to kill the pests. Other attempts include storing the beans in temperature-controlled warehouses to keep the pest activity to a minimum but without eradicating the infestation (CAOBISCO/ECA/ FCC, 2015). The use of pesticides on cocoa trees can also lead to the presence of residues in cocoa products. In various markets, there are now limits set for the maximum level of pesticide residues in cocoa beans. The cocoa industry requires that all supplies of cocoa beans and products comply with these limits and will closely monitor the levels of pesticide residues on all cocoa raw materials (Wood, 1985c; CAOBISCO/ECA/ FCC, 2015; CMAA, 2015b). Information on active compounds that are under review and newly introduced maximum levels and restrictions can be found on various websites as follow: • Codex Alimentarius [http://www.codexalimentarius.net/ pestres/data/index.html] • European Food Safety Agency [http://www.efsa.europa.eu/ en/panels/pesticides.htm] • European Commission [http://ec.europa.eu/environment/ ppps/home.htm and http://ec.europa.eu/sanco_pesticides/] • U.S. Environmental Protection Agency [www.EPA.gov/ pesticides] • Japanese Ministry of Health, Labor and Welfare [http:// www.mhlw.go.jp/english/topics/foodsafety] There is also a manual on the safe use of pesticides in cocoa growing (Bateman, 2015) and updates are available from http://www.icco.org/ sites/sps/manual.html. Food allergies can be fatal, so it is important that the supply chain is reviewed to identify if there are any allergenic components present, primarily through cross-contamination, so that allergen management systems be put in place during manufacturing. The last resort for consumer protection is information through indicative labeling on the package and in the ingredient listing (CAOBISCO/ECA/FCC, 2015). Heavy metals which are toxic to humans can be found in various agricultural raw materials. The presence of cadmium in cocoa beans and ultimately in chocolates and to a lesser extent lead are currently a major concern in many international markets. Once ingested, cadmium can accumulate in human tissue over time causing kidney

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and bone damage and is also a carcinogen. The EU has recently set maximum limits for cadmium in cocoa products which are applicable from 1 January 2019 (see Table 5.1). Cadmium in cocoa beans is limited to certain regions of some producing countries, particularly in Latin America and Caribbean areas (Ramtahal et  al., 2016). High levels in the beans are generally associated with naturally high levels of cadmium in the relatively young soils of these regions that are available for uptake by cocoa trees. However, levels are sometimes affected by a number of factors including the physical and chemical nature of the soil, the cocoa variety and anthropogenic factors including the use of contaminated fertilizers and incidence of flooding in cocoa growing areas (CAOBISCO/ECA/FCC, 2015; Ramtahal et  al., 2016). Research is ongoing to elucidate these factors and to mitigate against cadmium uptake (Ramtahal et al., 2015, 2016). Lead can occur naturally in the soil; however, factors including pH and organic matter content make it insoluble and not available to the plant. However, lead can be released into the environment when fossil fuels are burned as well as during forest fires, mining, smelting and petroleum extraction operations (Baligar et al., 1998). Cocoa beans, cocoa semi-finished products and chocolates are considered to be minor contributors to lead exposure and maximum limits for lead in cocoa (powder and beans) and chocolate products are not currently under consideration (CAOBISCO/ECA/FCC, 2015). Mineral oil hydrocarbons (MOH) contamination in cocoa beans and cocoa products can arise at various points in the value chain from the farm to the consumer. Contamination can occur during Table 5.1  EU Maximum Limits for Cadmium in Cocoa Products to Be Applicable from 1 January 2019 (Commission Regulation (EU) No 488/2014 Amending Regulation (EC) No 1881/2006) SPECIFIC COCOA AND CHOCOLATE PRODUCTS Milk chocolate with  80%) and elevated temperature (37°C), sucrose decreased by 35% whereas fructose and glucose contents increased six to twelvefold (Bucheli et al., 1996). In order to control the effects of high ambient temperature and humidity, shipment containers may be equipped with aeration devices. Moreover, different kinds of packaging materials (permeable and impermeable ones) and implementation of desiccant bags may be used. Finally, there are also experiments with the controlled atmosphere method using artificial carbon dioxide and/or reduced oxygen content (Kurzrock et al., 2005; Nobre et al., 2007; Ribeiro et al., 2011; Rekerdres, 2012; Borém et al., 2013; Lambot et al., 2013). Very recently, the application of edible biopolymer coatings to stored green coffee has been suggested as means of improving the storage of green coffee with particularly good results for starch as coating biopolymer (Ferreira et al., 2018). Therefore, the challenge of maintaining green coffee quality during storage and transportation may be best accepted with providing and maintaining optimum storage conditions (humidity, temperature, oxygen) and with otherwise roasting the coffee before it adapts old crop quality traits. 7.18 Coffee Monsooning

There is a coffee specialty from India, the west coast of Malabar regions, in which the principles of good green coffee storage seem to be inverted because, for a short time, the already dried, hulled and cleaned coffee beans are deliberately exposed to humidity and afterward re-dried again. This process is called monsooning, and it involves both Arabica and Robusta coffee which undergo changes in both the physical and biochemical properties. The resulting coffee is known to be distinguished from coffees without such treatment in taste, body, flavor, color and texture (Rao et al., 1971; Ahmad, 2000). For six to

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seven weeks during the monsoon season, the beans are exposed to moist winds in open warehouses and their water contents increase again to more than 16%. By taking up humidity, the beans swell, the size increases and a significant change in microstructure persists even after re-drying, and their color changes from pale, yellowish to light brown (Balyaya and Clifford, 1995; Ahmad, 2000; Murthy and Manonmani, 2009; Frisullo et al., 2012). It was reported that the taste of the brews prepared from monsooned roast showed less acidity and were more neutral and mellow, the organoleptic changes being reminiscent of aged coffees. The monsooning process may be considered as a solid-state fermentation which allegedly also involves a significant rise in temperature. The chemical changes in coffee beans submitted to monsooning are reported to concern the carbohydrate fraction, the proteins and the polyphenols (Balyaya and Clifford, 1995; Tharappan and Ahmad, 2006). Surprisingly, despite their well-known significance as coffee aroma precursors, so far there seems to be no scientific report on the putative impact of monsooning on the composition of free amino acids in the beans. It is essential to avoid undesired growth of fungi and bacteria during the monsooning treatment, which at first glance seem to be invited by the increase of water activity and the rise in temperature in the beans, as well as the favorable environmental conditions (Ahmad and Magan, 2002; Tharappan and Ahmad, 2006; Murthy and Manonmani, 2009). The application of fumigants or radiation to reduce microbes on the monsooned coffee, as it was earlier suggested by some researchers (Majumder et  al., 1961; Ahmad, 2000, 2003; Bhushan et al., 2003a,b; Variyar et al., 2003), certainly cannot be a satisfying solution nowadays. Such treatment is often restricted or even prohibited by the legislation of many coffee importing countries. Moreover, supplementary microbial decontamination would address the problem of the microbes only, and not quite that of their up to then produced mycotoxins. 7.19 Concluding Remarks and Open Questions

Today, there can be no doubt that during postharvest coffee treatment, the occurrence of various seed-specific metabolic reactions and events has been recorded. These reactions and events may occur in

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the viable seed or postmortem, and they may have or may not have an impact on the resulting cup quality. Provided there is a seed-specific impact, it may be desirable or undesirable. If so, should the reactions or events rather be extended or avoided? Some of the events may not matter at all. Since germination processes have been found to occur during wet processes, should they be favored? Would an extension of the wet phase be beneficial? Is water content over time the central key or are oxygen and ambient temperature equally essential? Should tank fermentation be aerated? Should germination-promoting agents be added, for example, gibberellic acid (GA3) or mannanases, or rather the opposite, for example, osmotic agents or abscisic acid, possibly inhibiting germination? Would fermentation-extending trials under tropical conditions be practical at all or would undesired microbial colonialization spoil the outcome, anyway? What about stress-triggered metabolism during fermentation and drying? Should the stressed coffee bean be relieved from the stressor as much as possible or rather be guided through the situation as rapidly as possible? If a re-wetting of the dried and hulled coffee beans during monsooning treatment has an impact on coffee flavor sought by many coffee connoisseurs, what would be the effects of re-wetting the coffee at earlier stages during drying provided microbial spoilage can be excluded? And if there is no appreciable short-term effect on green coffee quality and on the roast prepared from the fresh green coffee, one should also look at potential long-term effects like storability of the green coffee, and so on.

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8 Roastin g E quipment for C o ffee P roces sin g VA N Ú S I A M A R I A C A R N E I R O N O G U E I R A A N D T HOM A S KOZ IOROW S K I Contents

8.1 Introduction 8.2 Theory of Coffee Roasting 8.2.1 Product Temperature 8.2.2 Thermal Energy 8.2.3 Color 8.2.4 Water 8.2.5 Pressure 8.2.6 Volume Flow 8.2.7 Roasting Profile 8.2.8 Energy Supply 8.2.9 Exhaust Gas Incineration 8.2.10 Waste Heat Recovery 8.2.11 Optimizing the Roasting Process 8.3 Physical and Chemical Changes as a Result of the Roasting Process 8.3.1 Physical Changes 8.3.1.1 Color 8.3.1.2 Volume 8.3.1.3 Cell Structure 8.3.1.4 Density 8.3.1.5 Dehydration 8.3.1.6 Weight Loss 8.3.1.7 Oil Migration 8.3.2 Chemical Changes in Link with the Roasting Profile 8.3.2.1 Chemical Reactions 8.3.2.2 Progress of Gas Formation 8.4 Coffee Roasting Selection and Equipment

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8.4.1 Small-Scale Equipment 253 8.4.1.1 Sample Roaster 254 8.4.1.2 Shop Roaster 254 8.4.2 Pilot Plant or Laboratory Equipment 255 8.4.2.1 Color Analysis 255 8.4.2.2 Moisture Analysis 256 8.4.2.3 Density Analysis 256 8.4.2.4 Cupping 256 8.4.2.5 Extraction 256 8.4.2.6 HPLC and GC 257 8.4.3 Industrial-Scale Equipment 257 8.4.3.1 Drum Roaster 257 8.4.3.2 Tangential Roaster 258 8.4.3.3 Centrifugal Roaster 258 8.4.3.4 Fluidized-Bed Roaster 259 8.4.3.5 Continuous Roaster 259 8.5 Science behind the Roasting Process 260 8.5.1 Engineering 260 8.5.2 Chemistry 261 8.5.3 Physics 262 8.6 New Approach and Novel Technology for Coffee Roasting 262 8.7 Concluding Remarks 264 References 265 8.1 Introduction

The roasting process is one of the most important steps in transforming green coffee into the tasty coffee beverage. Arising from a few initial chemical compounds during the roasting process are numerous volatile aromatic compounds. The roasting process produces a dry and brittle texture which facilitates the crushing of the coffee beans and increases the extraction capability. Coffee is roasted by dry heating which, unlike what is usual for many other natural products, is terminated at relatively high temperatures of up to 250°C. The transmission of heat to the surface of the coffee beans takes place by means of convection, radiation and conduction. Heat conduction inside the beans progresses from the outside inward. The most important parameter in the roasting process is

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the specific quantity of thermal energy made available to the coffee beans. The coffee temperature profile, that is, the course of the coffee temperature throughout the roasting time, is dependent heavily on it. The temperature profile is therefore the decisive parameter for homogeneous roasting as well as for the physical changes and chemical reactions. The degree of roasting, that is, the color of the roasted coffee, has an essential influence on the formation of aroma and development of the flavor, and is thus mainly responsible for the quality of the roasted product and ultimately the coffee beverage. Moreover, the roasting time has an influence that is not to be neglected. A satisfactory assessment based on the roasting degree without knowing the roasting time is if at all hardly possible. Essentially, the roasting time and roasting degree determine the coffee temperature profile. Within the roasting time, the course of the coffee temperature profile can be influenced by the specific adaptation of the amount of thermal energy. Once the desired roasting degree is reached, as a rule, the hot coffee beans are cooled by means of ambient air. In the industrial process, the fully roasted coffee is in many cases quenched with water prior to the actual air cooling. Water quenching, once the roasting process reaches a specific product temperature or coffee color, brings the roasting procedure to an abrupt stop. This assures that uniform and reproducible roasting degrees are achieved from charge to charge as well as within the charges. The side effect from the addition of water could result in increased moisture content in the roasted coffee which in many cases is used to obtain very specific roasted coffee moistures. Various investigations and research concerning coffee roasting have led to far-reaching knowledge and to further development of coffee roasting equipment about which a survey is given in this chapter. 8.2 Theory of Coffee Roasting

The coffee roasting process is essentially related to the heat transfer process. The more this heat transfer can be influenced in different ways, the more specific roasting procedures can be developed. This roasting procedure, represented as the development of the product temperature over the roasting time, is described as a “roasting profile.” The term “profile roasting” has been derived which means that the

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temperature profile curve is graphed during the roasting process. A constant profile curve with a consistent quality of raw product implies a constant final product quality and coffee taste. The roasting process is a combination of three different kinds of heat transfer, namely conduction, radiation and convection. Conduction happens when hot substances come in contact, for example, with a hot roasting drum to coffee bean or hot bean to bean. Radiation happens without direct contact with the substances. Heat is absorbed or emitted in electromagnetic waves, and these carry thermal energy from one place to another, for example, hot material to coffee bean (without contact). Convection means the motion of a substance which carries the heat, for example, hot roasting gas to the coffee bean. During roasting, convective heat transport prevails as the coffee beans are continuously exposed to hot air. Roasting machines are technically designed with controllable and target-oriented heat conduction (forced convection). The efficiency of heat transfer increases with increasing relative speed between the airflow and the coffee bean movement as well as through the temperature difference between the bean surface and heating gas. Convective heat transfer drops with decreasing temperature difference. The beans should be permanently kept in proper motion (moving drum, paddle system, etc.) through, for example, mechanical built-in components so that the bean surface is exposed everywhere to the same approach flow conditions. Thus, the heat transfer during the coffee roasting process can be described by Equation 8.1. Heat transmission to the bean, Q (J):

ò (

)

Q = a A(t ) Tg -Tc (t ) dt (8.1) A(t) = Surface of the coffee bean (m2) Tg = Temperature of the heating gas (K) Tc(t) = Temperature of the coffee bean (K) T = roasting time (s) α = heat transfer coefficient (W/m2K)

As can be seen, the parameters within the equation constantly change during the roasting process. To be able to find out which is the

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present point of the process, certain parameters are documented during or at certain points of time during roasting. (Clarke and Macrae, 1987; Eggers and Pietsch, 2001; Eggers, 2004; Jansen, 2006). 8.2.1 Product Temperature

The heat transfer in the coffee bean progresses from the outside to the inside whereas the transport of the mass of volatile compounds inversely from the inside to the outside. This leads, particularly in the initial phase of the roasting process, to great differences in temperature of up to approximately 50°C between the outer and inner bean layers. Only at the bean core temperature of approximately 150°C do the temperatures gradually approximate one another. Normally, many coffee beans are roasted at the same time in a roasting bin. The smallest charge of approximately 700 coffee beans is processed in a sample roaster. A big industrial roaster is filled with some five million coffee beans per charge. Contact between the individual coffee beans, as well as contact of the beans with the walls of the bin, have an effect on heat transfer. The fact is that the time in which the coffee is roasted or the rise of the coffee temperature substantially influences the difference between the coffee bean surface and core temperatures. The shorter the roasting time; the greater this temperature difference. For practical reasons, the bean pile temperature is measured and used for controlling and directing the roasting process. The bean pile temperature is comprised of the surface temperature of the coffee beans on the one hand and the ambient temperature on the other. Hence the bean pile temperature does not provide precise information on the absolute temperature of the bean surface. A comparison of this coffee temperature is possible only up to a point due to many influences such as coffee sort, bean size, roaster type, that is, roasting bin design, fill factor, position and type of thermocouple. The diagram in Figure 8.1 shows an example of the courses of the coffee temperatures during the roasting process. The graphic portrayal is only intended to give an impression and refers only to a very specific roasting process with very specific process parameters.

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8

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color (Colorette 3) [scale grad.]

temperature [°C]

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Figure 8.1  Temperature development during roasting.

8.2.2 Thermal Energy

Thermal energy is often determined by the input of the burner energy or burner adjustment or the roasting supply air temperature. The thermal energy required for a specific coffee temperature profile is heavily dependent on the coffee sort, the roasting degree and particularly on the moisture content of the raw coffee. The thermophysical properties of the coffee beans, such as thermal conductivity and heat capacity, constantly change during the roasting process owing to the different physical properties. The pie chart in Figure 8.2 shows an example of the theoretically calculated heat energy values for roasting Arabica coffee related to a very specific roasting degree based on 11.5% green coffee moisture. The energy released in the exothermal phase has been taken into account accordingly. The result of this is a specific heat energy requirement of 470 kJ per kg of green coffee. The proportion of exothermal heat used in this regard is roughly estimated. Precise statements on exothermal heat when roasting are not available at this point in time. The specific heat energy requirement comprises the required water evaporation energy, the energy for heating the residual moisture and the heat energy for heating the dry coffee substance. Of course, the released exothermal heat reduces the calculated energy for the roasting process.

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Figure 8.2  Thermal energy (unit: kJ/kg green coffee).

In Figure 8.2, the greatest share of the heat energy requirement is needed for evaporating the moisture present in the green coffee. This share can change depending on coffee moisture and roasting degree. At higher levels of green coffee moisture, the share of moisture to be evaporated is greater and inevitably also the requisite heat energy requirement. 8.2.3 Color

The color of the roasted coffee is an indication of the roasting degree and can help the operator to manage and control the process. The roasting degree is an extremely important criterion for the quality of the coffee. Coffee producers set a very specific roasting degree for every product offered on the market. The roasting degree is worked out based on market research, many years of experience and intensive sensory tests. 8.2.4 Water

Depending on the roasting operation, water can be injected to the finished roasted product at the end of the roasting process, and the roasting process can be stopped abruptly because the coffee gets cooled down within a few seconds to temperatures of approximately 120°C

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such that no further roasting continues. The coffee which usually has a moisture value between 0.5 and 1.5% at the end of the roasting, absorbs a certain amount of water and increases the product weight. By quenching the hot beans with water, the resulting water vapor causes extraction and removes certain substances from the roasted coffee. Depending on the coffee quality, this can be evaluated positively or negatively with respect to the taste development. 8.2.5 Pressure

In general, the roasting process runs slightly under pressure to prevent roasting gases from escaping out of the roaster. By changing the pressure during the roasting process, the taste profile can be influenced as well, including the development of aroma. 8.2.6 Volume Flow

The volume flow rate in combination with the temperature provides the roasting process with the necessary heat energy. Thus, volume flow is another parameter that can have a direct influence in determining the amount of available heat energy and how this can be transferred to the coffee beans based on the flow. 8.2.7 Roasting Profile

By combination and modification of the aforementioned variables throughout the roasting process, various roasting profiles with each of different and distinct features of taste can be designed. The graph in Figure 8.3 represents an example. Figure 8.3 shows three different roasting profiles which were generated by varying the roasting supply temperature and the volume flow. All three roasting profiles have the same roasting time and roasting color but with energy supply in the different roasting phases controlled differently. However, the sensory analysis clearly indicated the difference between the three coffees. The product from profile 1 had been perceived as roasted coffee with complex aroma and significant acid, profile 2 with considerably less acid and for profile 3 the flavor was described as abrasive acid.

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Figure 8.3  Roasting profiles.

8.2.8 Energy Supply

Different types of heating come into question for the generation of the required supply air temperature. Oil or gas burners can be used, although gas burners are preferable compared to oil burners due to better combustion properties, particularly when the energy is directly provided to the coffee. Smaller roasters might also be equipped with electrical heating devices, whereas the regulating behavior of the electrical heating must be observed here. Sometimes, the roasting supply air is even generated by wood ovens, because wood is available as a low-cost and energy-neutral source in many countries where coffee is cultivated. Furthermore, unusual types of heating for energy generation like coal, hot sand, microwaves, vapor, and so on, are also sometimes being used. Due to restrictions concerning operation, maintenance, safety or simple controllability, the utilization of gas burners has become standard for industrial roasting processes. 8.2.9 Exhaust Gas Incineration

Increasing and more rigorous country-specific requirements regarding environmental protection demand not the only filtration of the chaff and other particles, but the exhaust gases arising from the roasting and grinding process have to be treated as well. During roasting, it is mainly volatile carbon compounds (Cx), carbon monoxide (CO) and

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carbon dioxide (CO2) and while grinding it is mainly carbon dioxide (CO2). Carbon dioxide can, for the most part, be reused as a protective gas for the conveying devices and silos in the coffee grinding process. Impurities in the exhaust air of the roaster are generally eliminated through thermal and/or catalytic incineration. Catalytic incineration is the current most state of the art development, and precious metals like platinum serve as catalysts. The burning process takes place at temperatures between 450 and 600°C. For regenerative thermal oxidation, the input of energy needed for exhaust gas incineration can be substantially reduced. In this procedure, the energy released by the flameless burning of the pollutants is buffered in a ceramic bed and for the most part redirected back into the process, which as a result attains a thermal efficiency of 95 to 98%. Owing to the high-process temperature of 900 to 1000°C, the limit prescribed for pollutant emissions are clearly undershot (VDI, 2015). 8.2.10 Waste Heat Recovery

Substantial energy savings are possible not only through exhaust gas incineration but also in the roasting process if the waste heat is recovered. In this case, the exhaust air stream, after having been purified in the centrifugal separator, is fed back into the roasting process. An alternative way of utilizing the excess energy of the exhaust air is for preheating the raw coffee. In this case, the hot air is siphoned off the exhaust air stream by means of a pipeline system and directed to a preheating bin. Here, the green coffee is heated to a temperature of about 100°C so that less heating energy is required for the subsequent roasting process. Green coffee preheating gives possible energy savings on the order of 20% and likewise a 25% reduction in carbon dioxide emissions. At the same time, the process efficiency of the roasting machine is boosted up by 20%. The procedure has no negative effects on the development of taste in the roasted coffee. During the roasting process, gases are produced due to the Maillard reaction and these are released in the roaster. Main components of this gas composition are CO2, CO and N2. The faster and darker the roast, the higher are the released gas quantities. When interacting with heated air and oxygen, these gases might reach a critical composition. Furthermore, possible deposits in the roasting system that consist of coffee oils have to be considered as being critical. The same

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goes for the coffee itself because exothermal reactions might occur at a certain temperature onwards and ignite. Therefore, attention must be paid to protection against possible dangers. The utilized control systems are usually equipped with safety functions or safety elements like automatic emergency water quenching, special sensors for determining temperatures and pressures or even CO measurement. 8.2.11 Optimizing the Roasting Process

In order to configure the roasting process as optimally as possible for each green coffee sort and every desired roasting quality, modern roaster control systems make it possible to define and monitor specific roasting profiles which comprise of roasting time, roasting degree and temperature profile as well as the sorts, storage temperature and moisture content of the green coffee. Sensors continuously monitor the actual temperature of the coffee beans and the energy supply is regulated according to the target values set in the profile. The “profile-roasting” type of roasting control system can be implemented in nearly all recently built batch roasters and enables reproducible results of high-quality products. The process “reflection roasting” goes one step further by influencing the heat flow profile in the interior of the coffee bean as precisely as possible. By means of pneumatic-correcting elements, the air supply to the roasters, and thereby the temperature, is modulated such that the actual temperature curve approaches the target curve very quickly. Differences between green coffee batches such as varying temperature values or moisture values or different states of the machines at the start of roasting a different batch size or the cold start of the roaster after a production stop can all be compensated by reflection roasting. For this reason, the process is of particular interest for products which require very consistent roasting results like ground coffee for pods or capsules. The configuration of the roasting process and therefore aroma development can either be influenced by the roast master himself or by an intelligent control system. As the taste and the aroma sensation around the world can vary enormously, the focus is on the available possibilities for selecting the influencing factors. The selection of the green coffee sort and of the roasting course in order to influence the roasting result belongs to the basic decisions that have to be taken.

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The aroma configuration can also be influenced by selecting the type of blending. There are different approaches to how and at what point of time the blending should be done. Each of these blending types has advantages and disadvantages with regard to effort, cost and required space, and so on. Each producer must find an approach that suits their individual conditions and possibilities. When using “blending before roasting,” the green coffee sorts are mixed before roasting and are roasted together. When using the “blending inside roaster,” the sorting with the higher energy requirement is filled into the roaster first, for example, as is the case for Robusta. After a determined period of time, the sorting with the lower energy requirement is filled into the roaster. When using “blending after roasting,” the respective individual sorts are roasted individually and are mixed as roasted coffee later. Another variant is “blending after grinding.” In this case, the grinding degree of the different sorts or blends to be mixed can also be adapted. Another method for configuring the aroma is the interrupted roast where the roasting is interrupted at a certain temperature point in order to complete the roast, for example, the following day. The aroma can also be configured by adding additional substances. For example, when producing “torrefacto” coffee, sugar is added at the end of the roasting process and the caramelized sugar results in a bitter taste. In other countries, corn, cardamom or even butter is added to the coffee in order to fulfill regional aroma preferences. There are really diverse possibilities for shaping aroma developments in a targeted way. By selecting the green coffee sort and the related parameters, like growth process, cultivation location and height, certain quality attributes like acid, fruity notes, body, and so on, can be determined decisively. By selecting the roasting time, the acidity or bitterness of the roasted coffee can also be influenced very strongly. When using roasting times of up to 4 min, a considerably higher acid proportion is achieved. When roasting coffee longer than 10 min, the bitter notes increase. Moreover, lightly roasted coffees have a higher proportion of acidity, higher acrylamide values and lower furan values. The darker the roast, the harsher and bitter the taste whereas the acrylamide values decrease and the furan values increase. The selection of roasting time also has an influence on the degassing behavior of the roasted coffee. Due to the strong pressure buildup

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of up to 25 bar within one coffee bean when using a short-time roast and due to the larger stored gas volume, this coffee degasses faster than coffee that had been roasted for a long time. As a long-time roast does not add the energy so quickly, there is less pressure buildup and a slower degassing. If roasting beyond the second crack, so-called “micro-cracks” occur in the cell walls of the bean which prevent the cell from storing the enclosed gas as long, so shorter degassing times occur again (FEI, 2011; Koziorowski, 2011; Wieland et  al., 2011; Yeretzian et al., 2012). 8.3 Physical and Chemical Changes as a Result of the Roasting Process

Before discussing physical changes and chemical reactions when roasting coffee, it is absolutely necessary to consider that green coffee is a natural product. Like everything that grows naturally, every single coffee bean has its own individual features. 8.3.1 Physical Changes

As a result of the roasting process the major share of the moisture present in the green coffee evaporates; the coffee beans expand and the color of the beans changes. The thin surface skin of the bean loosens itself from the coffee bean. The loss of moisture and expansion of volume in the coffee bean give the cellular tissue a dry and brittle texture. This eases the crushing of the coffee beans and increases the extraction capability (Geiger, 2004). 8.3.1.1 Color  The color change sequence runs from tender green to yellow, yellow-brown, light brown, dark brown to black-brown. Yellowing starts at ca. 130°C. From this phase on, a gradual change from light to dark takes place. The color of the roasted coffee is an indication of the roasting degree and can aid the operator in steering and controlling of the process. The color of the bean surface alone, although useful as a comparative magnitude for roasting, does not allow a clear statement to be made about the roasting degree as a whole. Especially for very a short roasting time, it can be expected that the color in the core will remain lighter than the bean’s surface.

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For this reason, the relationship between roasting degree on the one hand and color value, on the other hand, is only meaningful by assessment of the coffee in a ground state. There is no standard, that is, standardized procedure, for the color determination of roasted coffee. Various manufacturers of color measuring instruments each have their own scale graduation which cannot easily be compared among one another. Terms like “light,” “medium,” “dark,” and so on, enable a rough classification of roasting degrees but are insufficient for making qualitative and economic statements. 8.3.1.2 Volume  The volume of the coffee bean expands during roast-

ing. The formation of steam and gas cause a high buildup of pressure inside the cells of the beans and induces swelling. The permeability of the cell periphery, that is, the porosity, is not enough to allow the steam and gas to escape in time without a pressure buildup. The bean structure, the green coffee moisture, and the coffee temperature profile during roasting has a decisive influence on the expansion of the beans. According to the coffee sort, roasting time and roasting degree, the increase in volume can more than double. Generally, there is a tendency in all coffee sorts toward a decrease in volume for extended roasting times and an increase in volume for shortened roasting times.

8.3.1.3  Cell Structure  A cross-section of the longitudinal axis reveals the special structure of a coffee bean (Figure 8.4). The cotyledonal tissue with the embryo in the middle is rolled up like a balled fist. The strip of tissue originating from the embryo is two-plied and is separated from the “mucilage” by a mucic layer. The space between these two layers can increase through a heightened

Figure 8.4  Green coffee bean (Brazil).

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buildup of pressure during roasting. The silver skin found on the outer surface of the coffee bean is clearly recognizable. The silver skin found in the bean notch does not form such a firm connection with the cellular tissue. The more or less loose skin is held by the curved form of the notch. The tissue of the coffee bean (parenchyma) is composed of many cells. The cell core is enclosed in a thin, semi-permeable cellular membrane and bordered by a solid, cellulose-like cell wall. The compacter cell structure is clearly visible at the outer edge of the coffee bean. A single Arabica coffee bean happens to be composed of approximately one million single cells. Each one of these cells makes its contribution to the end results. During roasting and through the formation of steam and gas (mainly carbon dioxide) there is a high buildup of pressure inside the cells and the cell volumes expand. Due to the expansion of the cell peripheries, the cell walls become thinner and the micropores become larger. Moreover, the periphery has become more brittle through the loss of moisture. Inside the cell, an equilibrium develops between the built-up pressure and the permeability of the cell structure. 8.3.1.4 Density  The loss of mass and expansion in volume dur-

ing roasting result in a reduction in the density of the coffee bean. Bulk density is important for warehousing and packing and is usually expressed as the mass (g or kg) occupied by a volume of 1 dm³ or 1 m³, respectively. Owing to the loss of mass, the high short-term loss of moisture in the roasting time range from 5 to 6 min is automatically mirrored in the bulk density. The course of the residual moisture and that of the bulk density is practically identical. Volume expansion during the roasting procedure has an effect on the bulk density of the roasted coffee beans.

8.3.1.5 Dehydration  Dehydration progresses in two stages during roasting. Up to a temperature of ca. 100°C evaporation takes place and subsequently vaporization. Up to a coffee temperature of 100°C, the free moisture on the surface of the coffee beans will be taken up by the ambient air. Once the boiling point of 100°C is reached, vaporization sets in.

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In the roasting process, the vaporization of moisture is important for economic efficiency and quality of the roasted coffee. Yield, that is, substance loss, energy requirement as well as the course of the physical and chemical processes, are influenced by the original quantity of moisture in the green coffee. The moisture content has a substantial influence on the behavior of the coffee beans during roasting. Thermal conduction in moister coffees, for instance, is higher than in dryer coffees. Green coffee, as a rule, has an approximate initial moisture concentration of 8 to 13% before roasting. The post-roasting moisture concentration in the roasted coffee beans lies between 0.5 and 3.5% according to coffee sort, roasting time and roasting degree. The influence of possible water quenching at the end of the process is not taken into consideration here. Besides being dependent on the temperatures, the reactions taking place during roasting are also dependent on the prevailing pressures. Because of this, the water quantity in the green coffee not only has an influence on the transfer of heat but also on the course of many individual reactions. The darker the coffee, the less moisture is left over. At shorter roasting times, lesser moisture is vaporized, whereby more residual moisture remains in the roasted coffee compared with longer roasting times. 8.3.1.6  Weight Loss  Weight loss during roasting, also known as sub-

stance loss, is associated with the moisture content of the green coffee, with the physical and chemical changes in the coffee and with the waste-gas behavior. The total loss of weight can fluctuate between 12 and 23%. Loss of skin is not included in the substance loss. Foreign particles, tiny stones in particular, which are not removed in advance during cleansing, can naturally affect the results of substance loss. Moisture loss (9–12% points) makes up the greatest proportion of weight loss. Related to the dry substance, the loss of carbon dioxide compared with all other compounds is the greatest by far. Skin loss pertains mainly to the silver skins found on the outside surface of the bean. Depending on the green coffee sort and the quality, a greater or lesser quantity of skin is to be expected. Unlike the surface skins, the silver skins found in the notch of the entire bean are not removed until grinding. In industrial coffee roasting, water quenching is implemented to abruptly stop the roasting sequence once a specific coffee temperature

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or coffee hue has been attained. This ensures that reproducible roasting degrees can be achieved from charge to charge. By prescribing this water charge quantity, an increase of moisture content in the roasted coffee can be achieved. The yield, that is, the weight loss, will automatically be positively influenced thereby. However, the effect of the moisture content on the quality of the roasted coffee should not be underestimated, particularly in connection with the shelf life of the coffee. Owing to the high gas pressure in the cells of the coffee bean, gas will be constantly released until pressure equilibrates with the surrounding. Chiefly dealt with here is carbon dioxide, and this gasrelease behavior results in weight loss. Different amounts of loss are to be expected according to coffee sort, roasting degree and roasting time. The average total gas-release amount is ca. 0.8%. After a dwell or storage time of 2 hr, loss of weight can be amounted to 0.05%, and after 8 hr ca. 0.1%. 8.3.1.7  Oil Migration  The major portion of the lipids already in the

green coffee, that is, the non-volatile fats and oils, will not be changed quantity-wise in the course of roasting. The greatest share of lipids by far is present in fluid form inside the cells. A portion of the enclosed lipid migrates, aided by the movement of gas, toward the surface of the coffee bean. Escape is prevented or at least retarded by the dense structure of the cellular tissue in the area of the bean surface. For certain types of roasting, especially for short roasting times and dark roasting degrees, the sporadic escape of liquid fat particles cannot be prevented. Isolated and fine drops of fats that form on the surface of the bean after roasting known as “sweating coffee.” 8.3.2 Chemical Changes in Link with the Roasting Profile

During the roasting process, many complex reactions take place which give the coffee its color, taste and typical coffee aroma. The Maillard reaction as well as pyrolysis, hydrolysis and gas formation play an extraordinarily important role in this regard (Hofmann et al., 2008). 8.3.2.1  Chemical Reactions  For coffee roasting, the Maillard reaction

is important with respect to coloration and aroma.

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Hydrolysis is a chemical reaction in which a chemical compound is decomposed through the action of water. A part of the chlorogenic acids, for example, is converted through hydrolysis into quinic acid and caffeic acid. Pyrolysis designates the thermal decomposition of complex substances. Up to a coffee temperature of ca. 160°C, the chemical reactions are endothermic, that is, under thermal absorption. In the temperature range of 160 to about 250°C, the transfer of heat is augmented due to exothermic reactions (pyrolysis). At a coffee temperature of around 220°C, the exothermic reaction is at its highest. 8.3.2.2  Progress of Gas Formation  From about 1000 different components, almost 850 different volatile aromatic components have been identified to date. The major portion is made up of volatile aromatic compounds. The development of the aromatic compounds is for the most part dependent on the roasting degree of the coffee. The roasting degree influences not only the formation but also the decomposition of diverse aromatic compounds. Some volatile compounds increase in quantity with an increased roasting degree, others, in turn, increase to a certain roasting degree and subsequently begin to decompose when the roasting degree continues to rise. Moreover, there are volatile aromatic compounds that after a tendency to increase and decompose are recomposed again in the course of roasting. Increasing coffee temperature causes the number of gaseous compounds being released to rise. Roasting time also has an effect on the aroma development in which the acid content and thereby the acidic taste of the coffee increases with the reduction of the roasting time. Incidentally, the effect of roasting time on the acidity of light roasted coffees is greater than on dark roasted coffees. The gas mixture, comprised of nitrogen, carbon dioxide and carbon monoxide, far exceeds all of the other volatile substances in the coffee. Due to the formation of steam and gas, the pressure in the cells increases. The gas mixture seeks an escape route at the weakest spots of the coffee bean under high pressure. At a specific roasting degree, an audible cracking can be noticed. In the area of the weakest

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spot, sections of the bean are abruptly burst, giving rise to the typical cracking sound and hairline cracks form in this area. Further along in the course of roasting, a second cracking occurrence can come about, especially for dark roasting degrees. The first audible cracking is mainly due to the escape of steam; however, the second cracking is caused mainly through the formation of carbon dioxide. A certain percentage of the gas, under considerable overall pressure, remains in the cells of the coffee beans. The quantity of gas remaining in the cells immediately subsequent to roasting is also dependent, apart from the coffee sort, on the roasting degree and roasting time. When the roasting degree is increased and the roasting time is reduced, the residual quantity in the coffee bean increases. The gas enclosed in the cells is released by diffusion until pressure equilibrates with the surroundings. The speed of degassing for roasted coffee beans is very slow due to the relatively small outer surface and long diffusion paths. 8.4 Coffee Roasting Selection and Equipment

The two most common roasting processes are continuous and batch roasters. The continuous roaster is filled and emptied continuously while the batch roaster works according to a defined roasting cycle (Verlag Moderne Industrie, 2007). 8.4.1 Small-Scale Equipment

In many countries, the pan or small iron balls and drums, into which a small amount of beans is filled, are still being used for the roasting of coffee in a traditional way. For the roasting of small quantities, the equipment must permit only heat transfer. At the same time, the equipment in question is nowadays equipped with additional sensors, for example, for temperature, pressure, moisture and noise measurements. Then, the roasting process can also be represented visually via data logger or freely available software programs. Various smaller mini-roasters are also developed for domestic use, and a quite extensive framework would be required here when responding to all possible mini and small roasters. This is why more

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details are provided with regard to sample roasters, shop roasters and industrial roasters. Generally, everyone tries to optimally realize his own type of roasting process design. In this context, one often talks about artisan or specialty roasters. All, however, have in common the achievement of influence on the aroma development and optimal taste experience for one’s own understanding via the modification of certain parameters like roast supply air temperature, roast air volume flow, mixing speeds and pressures, and so on. Many roasters are equipped with a sampler so that the roasting process can be pursued and the influence of the different adaptations can at least be directly optically assessed. A small number of beans can thus be withdrawn again and again and directly assessed. Each of these roasters also has its special roasting process owing to the type of heat transfer, the arrangement of the measuring points or the adjustment options. This means, however, that individual results cannot be simply transferred from one roasting system to another. Here, the roaster operator’s experience is of significance; he/she should be familiar with the corresponding system’s peculiarities. 8.4.1.1  Sample Roaster  Particularly low quantities can be roasted in

this small roaster, mainly manufactured as a table roaster. In most cases, sample roasters are designed as drum roasters. The application of sample roasters are already initiated at the coffee farms to assess the quality of the coffee harvest. During the further supply chain of the green coffee, these sample roasters are used by green coffee dealers and roasting houses in order to assess the supplied green coffee. Applications can also be found in laboratories and universities for scientific roasted coffee studies. Batches of mainly 50–100 g green coffee beans are roasted in this roaster. The sample roasters are not only used as an individual unit but also in groups, so-called “batteries” with two, four or six drums, so that as many samples as possible can be analyzed at the same time or in parallel. Gas or electrical heating devices are usually installed to generate the necessary heat. 8.4.1.2  Shop Roaster  Special blend and roasting processes could gen-

erate individual taste profiles in small batches instead of the mass production in large-scale roasting plants. This is why small roasting

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houses are created and available with different performance data of batch quantities ranging from 1 to 60 kg of green coffee. This roaster is also often used as a marketing element and at a prominent location so that visitors can directly see it. Hence, the operator’s work on their roaster can be directly shown and explained. In such roasting houses, there is a requirement regarding the roaster which is to represent the brand of the roasting house accordingly. Drum roasters are widely used in shop roasting houses as this can be operated easily and warrants an optimal mixing and heat transfer. Various parameters can be adjusted, for example, burner capacity. The entire operation including the necessary maintenance should be clearly arranged and convenient to the user. The chaff liberated during the roasting process should be safely collected and easy to withdraw. These shop roasters should also be laid out in a modular fashion to enable simple completion which might for example be necessary for the exhaust air treatment. Then different types of thermal or catalytic systems up to systems requiring no additional energy, for example, zeolite filters, can be used for the exhaust air treatment. 8.4.2 Pilot Plant or Laboratory Equipment

For a roasting house which aims to offer its customers the same roasting result each time, the question arises concerning the best way to achieve this. Which data should or must be documented or recorded for quality assurance? How can these data be easily filed and evaluated? In answer to these questions certain standards for equipment for coffee roasting plants have been established (Illy and Viani, 1995). 8.4.2.1  Color Analysis  The color of roasted coffee beans can optimally

be measured when the product is ground as this is the appropriate way to represent the average color value of the bean. For this purpose, there are various colorimeters such as Agtron, Colorette, Hunterlab, and so on. It is important that the samples are always prepared in the same way for the color measurement regardless of the operator. As a first step, the sample should be ground using a disk mill with small amounts of beans. The same degree of grinding is a pre-condition for color comparisons. Afterwards, the sample should be stripped on a sample preparation unit to allow an even distribution of the surface

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without bruises. The prepared sample can then finally be placed under the light source of the measuring device. Usually, precise colorimeters do the measuring within the so-called three-dimensional scope of color; for example, L*, a* and b*. These values can be interpreted according to the range of colors defined by the color space. 8.4.2.2  Moisture Analysis  Moisture measurement can be done rapidly

using halogen analyzing units, NIR systems, microwave systems, and so on. These provide the result within a few seconds but the classical oven method can also be used. The oven method takes a longer time but is more accurate if done correctly. Therefore, for the other measurement methods, often one or several calibration curves with regard to different coffee sorts are stored. These curves have been generated by the oven method and this combination makes it possible to obtain a higher precision when using other methods.

8.4.2.3 Density Analysis  The purpose of the density analysis is to

obtain information concerning grain form and grain size as well as the basis for calculation of a filling space. The bulk density of a product corresponds to the quotient from the mass (in g) and the volume (in mL) under standard defined conditions. The tamped density of a product corresponds to the quotient from the mass (in g) and the volume (in mL) after having densified the product to a constant volume.

8.4.2.4 Cupping  Color, moisture and density are the so-called basic

quality parameters which are used in many roasting houses and laboratories. In addition, another parameter is the taste evaluation of the roasted coffee by the so-called cupping. Including this, these four parameters are sufficient for extensive appraisal and quality control. 8.4.2.5 Extraction  Larger roasting houses or laboratories have

established further methods to determine and control more quality parameters through extraction analyses. The water-soluble extract proportion refers to the proportion of extractable substances of the dry mass which is determined by extraction, subsequent drying and gravimetric determination. Furthermore, the pH value and the acidity (free acids) will be determined on the basis of this extract.

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8.4.2.6  HPLC and GC  Analysis by high-performance liquid chromatog-

raphy (HPLC) and gas chromatography (GC) are used to analyze single substances of the coffee; for example caffeine, 5-hydroxymethylfurfural, trigonelline, chlorogenic acids, organic acids, furane, acrylamide and phenol, and so on. The results of analyses can be taken for single quality features or can be aligned with the results of the sensory analysis.

8.4.3 Industrial-Scale Equipment

There exists no clear definition for the term “industrial roaster.” Mainly, it depends on a certain batch size and often the term “one bag roaster” (approximately 60 kg green coffee) is used. On the other hand, industrial roasters are equipped with fully automatic control and surveillance systems which make it almost unnecessary for the operator to stay beside the roasting machine. In its entirety referred to as a roasting system, which is composed of the actual roasting bin, the periphery, consisting of pipes, flaps and cyclones, the heating burner, an exhaust gas cleaning unit, the cooler and the roaster control (Siewetz and Desrosier, 1979; Schenker, 2000; Verlag Moderne Industrie, 2007; Deutscher Kaffeeverband, 2012). 8.4.3.1 Drum Roaster  The drum roaster is the most widely used

roasting system worldwide due to its simple design and long roasting times. The roasting bin is in the form of a reclining cylinder and for this reason it is called drum roaster. The drum itself can be designed in different types like completely perforated, completely plain cylinder or even double-walled. The drum roaster is filled and emptied at the front side. Hot air flows around and through the rotating drum. Special paddles on the inside of the roasting drum move the coffee against the hot air stream. This roasting system is characterized by a balance between convection (approximately 70%) and heat conduction (approximately 30%). To end the roasting sequence, the coffee can be precooled by adding water (quenching). Afterward, the drum lid is opened, and the coffee emptied onto a cooling sieve which is arranged in front of the roaster and through which cold air flows. The drum roaster is particularly suited for the production of highgrade coffee-like espresso or gourmet filter coffee. The comparably

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long roasting time enables this roaster to produce a gentle roasting over a long period of time and thereby develop complex aromas. The drum roaster is a classic method, and it can be designed in various sizes ranging from sample roaster, shop roaster and the industrial roaster with batches from 24 to 660 kg and roasting times from 8 to 20 min. 8.4.3.2  Tangential Roaster  The tangential roaster is a stationary, heat-

insulated roasting bin, on the inside of which is a paddle aggregate for turning and mixing the coffee beans. The green coffee is fed from a hopper into the roasting bin. The hot air stream is directed tangentially to the paddle aggregate and flows through the coffee beans. As with the drum roaster, a balanced transfer of heat is achieved, whereby the convective share is slightly dominant. When the roasting process is finished, the bottom flap of the roasting bin is opened and the roasted coffee gets emptied onto a flatbed cooler. By means of an intake of cold air, the beans are spun lightly and effectively cooled. Precooling by water quenching in the roasting bin is also possible with this roasting system. The tangential roaster is suitable for green coffee blends, problematic raw products such as small or widely different beans of for green coffees with a high proportion of breakage, as well as for frequent changes of the sort. This roaster can be filled with batch sizes from 23 to 750 kg and achieve an output of 500 up to 5000 kg green coffee per hr. The roasting times range between 1.5 to 18 min. 8.4.3.3  Centrifugal Roaster  The roasting bin of a centrifugal roaster is

shaped like a shell with an umbrella-shaped lid. During roasting, hot air flows through the shell and green coffee is filled into the shell. As soon as the bin is closed again, the shell begins to rotate on its vertical axis. The centrifugal force causes the coffee beans to distribute evenly across the entire surface of the shell. The beans move thereby toward the upper rim of the shell. Upon reaching the rim, the beans are deflected to the middle of the shell, back into the stream of hot air by lamellas in the lid. Quenching at the end of roasting is very effective owing to the large product surface. To empty the roasting bin, the shell is lowered and centrifugal force causes the coffee to flow over the upper rim into

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a ring-formed cooling sieve arranged around the shell. Cooling air is sucked evenly through the coffee, and the coffee is additionally loosened by means of nozzles fitted under the sieve. Nowadays, the shell is no longer lowered, but the emptying happens through a segment piece in the lid. Characteristic of the centrifugal roaster is the very homogeneous distribution of the coffee beans and the high share of convection in the transfer of heat. This results in very short roasting times and simultaneously a very uniform overall roasting. The capacity ranges between 300 and 4000 kg/hr with filling sizes from 32 up to 640 kg and roasting times from 1.5 to 15 min. 8.4.3.4  Fluidized-Bed Roaster  The fluidized or fluid-bed roaster was

developed as a system with the greatest possible share of convective heat. The beans are not set into motion mechanically but by the air stream. The green coffee beans are filled from above into the first of two identical chambers through the floors of which hot air is blown at high velocity. The beans are swirled upwards and, due to the shape of the roasting chamber, set into rotation. Heat transfer takes place mainly by means of the air current (convection). At the end of roasting, a slide at the bottom end of the chamber is opened, and the coffee beans fall into the second chamber. Through this chamber, fresh air flows for cooling purposes. This system is usually used for shorter roasting times and for higher bean qualities. This roaster operates batchwise with capacity ranging from 25 up to 400 kg. This leads to a capacity of 500 to 4000 kg green coffee per hr and roasting time is between 1.5 and 8 min. 8.4.3.5  Continuous Roaster  The continuous roaster differs from the

other roasting systems described as this roaster is continuously filled and emptied. The best-known design is the chamber system which consists of a rotating roasting drum which is divided into several chute-like chambers by half-high walls. The beans run through the roaster in small batches which are conveyed one chamber further in each rotation. A large number of nozzles blow hot air from above at high velocity onto the beans which causes them to swirl up so that heating is mainly due to convection. The chamber widths, number of nozzles and the flow speed vary along the length of the drum in order

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to accommodate the expanded volume and increasing temperature of the beans. In the final two stages of the chamber system, the beans are quenched and subsequently emptied onto a cooler belt arranged under the roaster. The cooler belt is made up of perforated plates through which cold air flows. This type of machine is especially suited to roast large quantities of a specific coffee product. It is less suitable for small quantities and for frequent changes of the sort although a change of coffee sorts “on the fly” is possible. The widely extended roasting time ranges from 1.5 up to 8 min allows continuous roasters to process a range of coffee qualities. These kinds of roasters have a capacity of 1500 to 4000 kg/hr. The special advantage of the chamber system is that in every phase of the roasting process, the beans are heated with an optimal supply of heat and flow. Furthermore, as the drum in this system is not perforated, coffee with a high percentage of fracture can be processed smoothly. Owing to the high proportion of convection, continuous roasters require very short roasting times with low shrinkage. Moreover, because the energy feed is steady and the exhaust gas concentration devoid of peak values, technical systems such as exhaust treatment and recirculation are easier and less expensive than is for the case of batch roasters. However, less continuous roasters are found in operation in the industry. 8.5 Science behind the Roasting Process

Today, we distinguish three main areas of science which are important to understand and control the roasting process namely engineering, chemistry and physics. Partially, these areas can still be subdivided but the further we progress with R&D, the more important it is to link these three areas in order to advance future trends and developments around coffee roasting. 8.5.1 Engineering

Modern roasting systems are designed in a recirculating way in order to reduce the use of energy during roasting by approximately 25%. Furthermore, more and more systems for the utilization of waste heat

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are used. One example is a heat exchanger that withdraws the energy from the hot exhaust air of the roaster in order to make this energy available again to other systems, such as the waste heat can be used again for air preheating in the burner. This does not restrict the flexibility of the burner system and directly leads to an energy saving of approximately 8%. Another possibility is preheating the green coffee where the cleaned exhaust air of the roasting process is directly routed to a preheating unit. The green coffee is heated to approximately 100°C and slightly dehumidified. Thanks to the higher input temperature and the lower dwell time of the coffee in the roaster, energy savings of 25% along with increased performance of 20% can be attained. Nowadays, catalytic exhaust air treatment systems are used during coffee roasting that has an operating temperature which is 100°C lower than the previous systems. Another system for the exhaust air treatment is the flameless, thermal oxidation where the lowest NOx concentrations and very low energy consumptions are achieved. On the other hand, engineers have to take safety aspects into consideration during roasting. As already described, a lot of gases can be released during coffee roasting. This might form explosive mixtures or lead to fires in combination with over-roasted coffee. Therefore, monitoring units or additional processes for simple control are introduced. Risk analyses, health and safety considerations, ATEX studies and safety calculations are standard measures when developing new roasting systems. For example, the utilization of thermal cleaning for cleaning the roasting system, CO measuring systems for monitoring the roasting processes, coupled with so-called dark roast process systems in order to safely produce very dark roasts. 8.5.2 Chemistry

Considerations and requirements concerning the chemical side also play an important role here. Chemical substances can be detected and determined in detail nowadays. In the last few years, intensive research concerning acrylamide, furan and dimethyl has taken place. Moreover, many scientific research studies have been conducted concerning the positive health aspects of coffee.

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Another scientific field of research is linked with the chemical and aroma compounds. It is better to record the roasting process using modern measuring technology, such as a PTR-ToF-MS system, as well as describing the procedures taking place during roasting (Gloess et al., 2012; Gloess et al., 2014; Zimmermann et al., 2014.) 8.5.3 Physics

Today, many sensors and measuring methods are used around the roaster in order to improve the roasting process. Pressure measurements coupled with air flaps render optimal control of the roasting process possible. With the help of moisture measuring sensors, the water quantities suitable for green coffee and the requested residual moistures can be adjusted. Statutory prescriptions about the residual moisture in the roasted coffee and quality aspects can be fulfilled in a simple and automated way. Online color measuring systems that continuously record color development during the roasting process also support the operator to respond to changes during roasting. 8.6 New Approach and Novel Technology for Coffee Roasting

In general, the trends and expectations of the market can be described by the terms flexibility, control, modularity, transferability, health, climate neutrality, individuality and diversification. The roaster, as well as the roasting process, must be configured and designed in a way that ensures the most possible flexibility for future applications. It can be expected that there will be more varieties of coffee sorts and blends for a widespread individualization of taste and quality. Therefore, a multitude of roasting profiles will be necessary with roasting times ranging from short, middle to long. At the same time, it must be possible to vary the course of the roasting profile in order to elaborate certain nuances of specific flavor groups. A particular roasting profile has to be developed, purposemade for the different systems of coffee brewing as there are filter, portafilter, capsules, pads, cold brew and French press, and so on. Another field is opened by the substance classes of the coffee. There are ingredients with attributes which are considered to have positive

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or negative effects on human health and the roaster must provide the opportunity to react accordingly. All these require wide-ranging flexibility of the roasting systems to control the roasting parameters as individually as possible and as safely as necessary. To assure the very specific function, there are control and monitoring systems required which can clearly and reliably record the single parameters of the process and the substances. Online and inline measuring and monitoring devices will be necessary and must be able to operate inside the roaster or within the roasting system under conditions of heat, moisture and pollution and still have an output of clear and solid measured data. Also, it will be necessary that those data run parallel to the roasting process and are directly available for the controlling of the plant. Therefore, samples of the gas steam have to be taken directly, and the time it takes for the evaluation has to be very short. These systems can help to make the roasting process safer which can also be used to identify unsecure situations early enough to react with purposeful solutions (Bock, 2000). The modular execution of the roaster with all the connected systems will be the target of construction in the future. This will allow easy solutions for assembling the line with additional units by modular extension or upgrades. Especially with regard to the changes of legal regulations, rules or norms which can be expected within the next few years, it will be easier for the manufacturer to react accordingly in order to take care of the climate, energy consumption and emission ratio. The manufacturer who wants to be well placed to face future challenges will need to be more aware of taking optimal advantage of his roasters’ opportunities. To find out the wide range and details of possibilities for operating the industrial roaster as well as creating new coffee products, the demand on small roasters for doing all the tests will rise steadily. The data and procedure results received from laboratory tests should easily be transferred to the existing roasting equipment. And this transfer should be carried out directly without any other transfer paths. Another aspect that will become more important, and is already known, is that coffee can be added to other substances or be combined with different products to achieve the desired health effect (Somoza, 2011).

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It can be assumed that the environmental regulations for the coffee roasting industry will be strengthened within the next few years. This can be answered by constantly finding better and new solutions for exhaust gas cleaning and energy efficiency. The existing basic approaches for developing environmentally responsible carbon-neutral roasting processes have to be intensified and expanded. For this purpose, the complete surrounding where the roasting equipment is installed including the supply and removal systems has to be considered to balance out the process as a whole. Another question is how individual domestic roasting will develop. If this becomes a trend, there will be a high demand for small, simple and safe roasting equipment which can be used at home. In general, it can be expected that in the future the user will wish to know special indicators of the roasting process and the roasting result. These data should be made accessible by presenting them in a simple graph which is easy to understand. The background to offer such simplicity is far more difficult. It depends on the coupling of superior controlling systems with the roasting process. This has already started and is expressed in terms like “Internet of Things,” “Smart Factory” or “Industry 4.0.” This overview shows that there is a large field of possibility and need to optimize the roasting process to still be able to meet the requirements in the future. 8.7 Concluding Remarks

In general, the desires and demands of the coffee consumer for his cup of coffee will dominate the lines of research around roasting matters in the future. The roasting machine together with the control and its operator will be the instrument for creating the desired aroma. For the industrial roasting process, it will still be of great significance for achieving constant coffee quality. At the same time, the introduction of new and specified roasting profiles will be distinctly different from those known today. The small market segment of specialty coffees, certain single sorts and specific sorts which are available only in small amounts will still be attended to by small roasting houses and shop roasters. The demand for “sustainable” coffee will be of prime importance to this segment.

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The larger roasting industry is always aware of the demands which occur in the market, but they only pick up the larger trends and design new industrial coffee products accordingly. Nevertheless, the roasting process will always depend on the operator who has the know-how to coordinate the plant and can react based on his knowledge and experience. Further, the composition of an optimum blend, mixed from different coffee sorts, requires the experience of product designers as well. All these can be supported by worldwide targeted research projects and by development in cooperation between industry and sciences.

References

Bock, J. 2000. “Selektives und rekalibrierbares Sensorsystem zur Messung charakteristischer Verbindungen in Röstprozessen am Beispiel der Kaffeeröstung.” (Dissertation) Justus-Liebig-Universität Gießen, Fachbereich Physik, Gießen, Germany. Clarke, R.J., and R. Macrae. 1987. Coffee. In: Technology, 1 (2), Elsevier Applied Science, London, UK. Deutscher Kaffeeverband, Hamburg. 2012. (Ed.), Faszination Kaffee. BucherVerlag, Munich, Germany. Eggers, R. 2004. “Zum Wärme und Stofftransport bei der Röstung von Kaffeebohnen.” In: Jahresbericht, 11–28. FEI (Forschungsvereinigung der Ernährungsindustrie), Bonn, Germany. Eggers, R., and A. Pietsch. 2001. “Technology I: Roasting.” In: Coffee. Recent Developments, eds. R.J. Clarke, and O.G. Vitzthum, 90–107, Blackwell Science, Oxford. FEI. 2011. Einfluss der Vorbehandlung und der Röstung auf Bitterstoffe in Kaffeegetränken. AiF 15752 N, F & E Dokumentation (Schlussbericht), Projekt der industriellen Gemeinschaftsforschung, Germany. Geiger, R. 2004. “Development of Coffee Bean Structure During Roasting; Investigations on Resistance and Driving Forces.” Thesis, Swiss Federal Institute of Technology (ETH), Zurich, Switzerland. Gloess, A.N., A. Vietri, S. Bongers, T. Koziorowski, and C. Yeretzian. 2012. On-line analysis of the coffee roasting process with PTR-ToF-MS: changes in flavor formation for different coffee varieties. Colloque Scientifique International Sur Le Café, Association Scientifique Internationale du Café (ASIC), Paris, France. Gloess, A.N., A. Vietri, F. Wieland, S. Smrke, B. Schönbächler, J.A.S. López, S. Petrozzi, S. Bongers, T. Koziorowski, and C. Yeretzian. 2014. Evidence of different flavour formation dynamics by roasting coffee from different origins: On-line analysis with PTR-ToF-MS. International Journal of Mass Spectrometry, 365–366:324–337.

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Hofmann, T., O. Frank, S. Blumberg, C. Kunert, and G. Zehentbauer. 2008. Molecular insights into the chemistry producing harsh bitter taste compounds of strongly roasted coffee. In: Recent Highlights in Flavor Chemistry and Biology, 154–159, eds. T. Hofmann, W. Meyerhof, and P. Schieberle. Dt. Forschungsanstalt für Lebensmittelchemie, Garching, Germany. Illy, A., and R. Viani. 1995. Espresso Coffee. The Science of Quality. Academic Press Limited, London. Jansen, G.A. 2006. Coffee Roasting. Magic – Art – Science. SV Corporate Media, Munich, Germany. Koziorowski, T. 2011. “Current trends and demands on roasting coffee and cocoa.” In: Book of Abstracts of the First International Congress on Cocoa, Coffee and Tea, eds. R. Travaglia, M. Bordiga, J.D. Coïsson, M. Locatelli, V. Fogliano, and M. Arlorio, 19–25, Blackwell Science, Oxford. Schenker, S. 2000. Investigations on the Hot Air Roasting of Coffee Beans (Ph.D. Thesis number 13620). Swiss Federal Institute of Technology (ETH), Zurich, Switzerland. Siewetz, M., and N.W. Desrosier. 1979. Coffee Technology. Avi Publishing Company, Westport, CT. Somoza, V. 2011. “Strategies for optimizing the health benefits of coffee beverages.” In: Book of Abstracts of the First International Congress on Cocoa, Coffee and Tea, eds. R. Travaglia, M. Bordiga, J.D. Coïsson, M. Locatelli, V. Fogliano, and M. Arlorio, 59–68. VDI. 2015. Emission Control Roasted-Coffee-Producing-Industry. Verein Deutscher Ingenieure, Beuth Verlag, Berlin, Germany. Verlag Moderne Industri. 2007. Industrial Coffee Refinement. SV Corporate Media, Munich, Germany. Wieland, F., A.N. Gloess, M. Keller, A. Wetzel, S. Schenker, and C. Yeretzian. 2011. Online monitoring of coffee roasting by proton transfer reaction time-of-flight mass spectrometry (PRT-ToF-MS) towards a real-time process control for a consistent roast profile. Analytical and Bioanalytical Chemistry, 401:1–2. Yeretzian, C., F. Wieland, and A. Gloess. 2012. Progress on coffee roasting – A process control tool for a consistent roast degree – Roast after roast. Newfood, 15 (3):22–26. Zimmermann, R., T. Streibel, R. Hertz-Schünemann, S. Ehlert, C. Schepler, C. Yeretzian, and J. Howell. 2014. Application of photo-ionization time-of-flight mass spectrometry for the studying of flavor compound formation in coffee roasting of bulk quantities and single beans. In: Proceedings of the 25th International Conference on Coffee Science, ASIC, Paris, France.

9 Fl avo r D e v elopment durin g R oastin g A D R I A N A FA R A H Contents

9.1 Introduction 267 9.2 Green Coffee Chemical Composition 269 9.2.1 Non-Volatile Composition of Raw Coffea arabica and Coffea canephora Seeds 270 9.2.2 Volatile Composition of Raw C. arabica and C. canephora Seeds 277 9.3 Roasting: Color and Flavor Development 277 9.3.1 Color Development 278 9.3.2 Chemical Changes and Flavor Development 280 9.4 Roast Profile and Flavor 286 9.5 Generation of Flavor Character and Off-Flavors 290 9.6 Factors Affecting Coffee Flavor after Roasting 296 9.6.1 Grinding, Packaging and Storing 296 9.6.2 Extracting Coffee Flavor: The Brew 297 9.7 Concluding Remarks 303 References 303 9.1 Introduction

The Cambridge Dictionary (2018) defines flavor as “how food or drink tastes” or “a particular taste itself.” Alternatively, it presents the definition of “a particular quality or character.” From a food science point of view, flavor has evolved beyond simple tastes to imply an overall or unified perceptual experience of a food that arises from the integrated signals of several sensory modalities, including taste, olfaction (smell), oral somatosensation (tactile, temperature and texture), oral nociception feeling (pain) and even also hearing (Fennema, 1996; Breslin, 2013; Spence, 2015). Although sight is not technically part 267

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of the flavor, like other indirect senses such as hearing and feeling, it strongly influences the perception of taste and olfaction and hence food acceptance (Fennema, 2017). Regarding the taste component of flavor, taste buds located on the tongue and in the back of the oral cavity interact with non-volatile compounds and enable humans to sense sweetness, acidity/sourness, saltiness, bitterness and umami sensations. Astringency is a tasterelated phenomenon, perceived as a dry feeling in the mouth along with a course puckering of the oral tissue (Fennema, 1996). In relation to smell, specialized cells of the olfactory epithelium of the nasal cavity account for orthonasal and retronasal olfaction. They detect low-molecular-weight volatile odorants responsible for the character of different foods, distinguishing mango from papaya and black tea from coffee, for example. The main volatile compounds responsible for the character of a food are usually impact compounds, which have strong odorant power and can be perceived in minor concentrations. However, isolated impact compounds won´t result in the same sensory experience as the ensemble of volatile compounds in a food matrix. Non-specific or trigeminal neural responses also provide important contributions to flavor perception through the detection of pungency, temperature, or delicious attributes, for example, as well as other chemically induced sensations that are incompletely understood (Fennema, 1996, 2017). Coffee flavor development begins on the farm during the growth and maturation of the fruit. But due to the poor aroma and unpleasant astringent taste of the seeds in their raw form, they are not used for brewing until they are roasted. During the roasting process, a number of chemical reactions take place to develop their typical, loved and quite complex flavor because, in addition to the numerous compounds already existing in coffee, hundreds of new non-volatile and volatile compounds are developed in the process (Farah, 2012). To date, more than 1000 compounds (Yeretzian et  al., 2003) have been identified in different roasted coffees, and certainly with the new postharvest and roasting technologies constantly being developed, there are still hundreds to be identified, especially the volatile compounds. This is because any technologies that affect the composition of flavor precursors, in addition to roasting parameters, will most probably affect the final brew.

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9.2 Green Coffee Chemical Composition

From over 100 coffee species currently cataloged (Davis et al., 2011), only two (Coffea arabica and Coffea canephora) have great economic importance. While a large number of C. arabica wild varietals and developed cultivars are traded around the world, concerning the C. canephora species, which traditionally tends to have lower market value, only two varietals are cultivated, Robusta and Conilon (the later originally called Kouilouensis, then Kouillon) which is particularly cultivated in Brazil. Commercially, both varietals may be called Robusta. The basic chemical composition of green or raw coffee seeds depends primarily on genetic aspects, especially those related to species. Even though within the same species the chemical composition suffers less variation among cultivars (particularly in countries where cultivars are originated from the crossing of related varietals), they can still hold important differences; for example, yellow cultivars like yellow bourbon tend to be sweeter and present a better cup. Hybrids of C. arabica and C. canephora tend to exhibit intermediate characteristics (Farah, 2012; Borém et  al., 2016). Wild varietals with singular chemical compositions have been found; for example, C. arabica cv. Laurina, which has half of the regular caffeine content (Silvarolla et al., 2004; Mazzafera et al., 2009). When comparing the chemical compositions of different cultivars, at least three consecutive crops of each should be evaluated to take into account natural metabolic fluctuations along physiologic cycles (Monteiro and Farah, 2012). As mentioned, C. arabica and C. canephora species differ in many ways. Regarding chemical composition and flavor, C. canephora seeds contain more soluble solids and therefore they are included in commercial blends to add body to the beverages and to increase yield. On the other hand, C. arabica seeds provide a superior cup quality and richer aroma. C. canephora commonly possesses lower acidity, milder flavor and, in light roasted coffee, it may present with a flat popcornlike aroma. For most Eastern consumers, some C. arabica seeds are needed for a blend to seem like coffee. However, selected C. canephora seeds, when carefully cultivated, harvested and processed may produce a better cup than a number of C. arabica blends, especially those containing low-quality defective seeds (Farah, 2012).

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Although most constituents of C. arabica are also present in C.  canephora, their relative distribution can differ considerably between species. Additionally, C. canephora contains a few secondary metabolites (e.g., minor chlorogenic acids isomers and diterpenes) that are not present in C. arabica and vice versa. Hybridization efforts have attempted to combine the resistance to diseases and other positive aspects of C. canephora seeds with the cup quality of C. arabica seeds, but it is likely that the traits responsible for pest resistance in C. canephora plants are partially responsible for the lower cup quality. 9.2.1 Non-Volatile Composition of Raw Coffea arabica and Coffea canephora Seeds

A simplified description of the chemical composition of green or raw C. arabica and C. canephora seeds is given here. The moisture content of the green seeds of C. arabica and C. canephora generally varies from approximately 10 to 12%. Above this level, the moisture is undesirable for flavor/cup quality, since it increases water activity and therefore the probability of microbial growth (Farah, 2012). Carbohydrates such as monosaccharides, oligosaccharides and polysaccharides are major coffee flavor constituents and often account for 59–62% of its dry weight in C. arabica and C. canephora. Polysaccharides (soluble and insoluble) account for approximately 50–54% of dry weight (Simões et al., 2018). However, in green coffee only about 2–4% of the polysaccharides are soluble. Sucrose is vital for coffee flavor and quality; it accounts for about 6 to 11% of C. arabica dry weight and approximately half (3 to 7%) in C. canephora. The higher sucrose content is one of the reasons for the higher cup quality and acidity of C. arabica compared to C. canephora (Farah, 2012; Borém et  al., 2016; Farah and Lima, 2018). Small amounts of monosaccharides, such as fructose, glucose, mannose, arabinose and rhamnose, as well as oligosaccharides such as raffinose and stachyose, are usually present in green coffee (Flament, 2002; Farah, 2012). However, in fermented coffees during postharvest processing, the number of simple sugars can get considerably higher (Neto et  al., 2017). Carbohydrates are precursors for the Maillard (in the case of sucrose, after inversion) and caramelization reactions, which are important for color and aroma development during roasting. They also contribute to the development of the brew’s acidity.

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Galactomannans are polymers of 1,4-linked mannans with a single galactose unit side chain at C6, and type II arabinogalactans consist of the main chain of 1,3-linked galactose branched at C6, with side chains containing arabinose and galactose residues (Díaz-Rubio and Saura-Calixto, 2007). The hot water-soluble green coffee type II arabinogalactans are highly branched and covalently linked to proteins in which 10% of the amino acid chains are 4-hydroxyproline residues. These polysaccharides are extremely complex. In addition to galactose and arabinose, they also contain raminose and glucuronic acid residues, as well as rhamnoarabinosyl and rhamnoarabinoarabinosyl side chains (Nunes et al., 2008). They are present in higher amounts in dry processed coffees that fully maintain their external thin mucilagenous material called silverskin. Cellulose and hemicellulose are also present in the raw and roasted coffee seeds, but due to their low solubility even after roasting they are not present in the brew. However, they serve as aroma precursors. Nitrogenous compounds account for about 15% of the green coffee chemical composition, with a slightly higher content in C. canephora compared to C. arabica (Farah, 2012). Protein, peptides and free amino acids alone account for 11.5% of coffee seeds dry weight in both species (Mazzafera et al., 2018). The most abundant protein is the 11s-globulin seed storage protein, representing about 45% of total dry weight. One-third of total coffee seed protein content is thought to bind to arabinogalactans in the cell wall; among them are enzymes such as polyphenol oxidase and peroxidases. The largest fraction of proteins remains in the cytoplasm. About 30 peptides with molecular weights ranging from 4 to 10 kDa have been identified in coffee seeds (about 0.5% of seeds dry weight). Methionine seems to be the least abundant amino acid, while glutamic acid/glutamine, aspartic acid/ asparagine and glycine are the most abundant in both coffee species (Mazzafera et al., 2018). As with carbohydrates, proteins, peptides and free amino acids are vital for coffee flavor, since they are needed for the Maillard reactions to occur. Free amino acids (0.15–2.5% dry weight) and peptides play a pivotal role in coffee quality. They (especially free amino acids and peptides) serve as precursors for the formation of important classes of volatile and non-volatile compounds, which contribute aroma, color and body to the brew. Objectionable biogenic amines, however, have been associated with enhanced amino acid contents in defective coffee

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seeds (Toci and Farah, 2014; Czech et  al., 2016; Mazzafera et  al., 2018). A number of additional minor nitrogenous compounds exist in green coffee including enzymes. Caffeine is a bitter alkaloid which is heat stable, and its concentration in C. canephora is approximately twice that found in C. arabica (Farah, 2012). Traces of additional methylxanthines (theophylline and theobromine) have been reported in green seeds as caffeine metabolites (Mazzafera et al., 2009). Trigonelline is another (slightly) bitter alkaloid biologically derived from enzymatic methylation of nicotinic acid. It is a precursor for the formation of different classes of non-volatile and volatile compounds during roasting. The amount of trigonelline in C. canephora is approximately two-thirds that found in C. arabica (Farah, 2012). Lipids make up a major fraction of coffee, and its contents vary considerably between C. arabica and C. canephora species. The total lipid content in C. arabica seeds (14/100 g dry weight) may double the content in C. canephora seeds (Stephanucci, 1979). The lipid fraction of coffee is composed mainly of triacylglycerols (approximately 75%), free fatty acids (1%), sterols (2.2% unesterified and 3.2% esterified with fatty acids), and tocopherols (0.05%), which are typically found in edible vegetable oils (Cavin et al., 2002; Köling-Speer and Speer, 2005; Speer Köling-Speer, 2006; Farah, 2012; Toci et al., 2013). Fatty acids in coffee are found primarily in combined forms; they are mostly esterified with glycerol in the triacylglycerol fraction, 20% esterified with diterpenes and a small proportion in sterol esters. Most fatty acids in coffee are unsaturated. Linoleic acid (18:2(n-6)), oleic acid (18:1(n-9)), and linolenic acid (18:3(n-3)) account for approximately 43–54%, 7–14%, and 1–2.6% of the triacylglycerol fraction, respectively, and approximately 46, 11 and 1% of the free fatty acid fraction, respectively (Lercker et al., 1996; Nikolova-Damyanova et al., 1998; Farah, 2012). The lipids fraction also contains diterpenes in proportions of up to 20% of the total lipid fraction (Cavin et al., 2002; Köling-Speer and Speer, 2005; Speer and Köling-Speer, 2006; Farah, 2012; Toci et al., 2013). The diterpens cafestol and kahweol are pentacyclic alcohols based on the kaurane skeleton. Methylated forms of cafestol and kahweol have been identified in Robusta seeds (Köling-Speer and Speer, 2005) and 16-o-methylcafestol has been proposed as a tool for species

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differentiation. Additionally, the amount of kahweol in C. canephora is negligible compared to C. arabica (Czech et al., 2016). Cafestol is the primary constituent of the unsaponifiable fraction of coffee oil, accounting for approximately 0.2 to 0.6% of coffee weight. Kahweol is more sensitive to heat, oxygen, light and acids and is therefore less abundant (Flament, 2002). Higher levels of diterpenes are found in C. arabica compared to C. canephora. Other identified components are coffeadiol and arabiol I, which have structures similar to the diterpenes cafestol and kahweol, respectively, but with different substitutions in the furan ring (Speer and Köling-Speer, 2006). Small amounts of the carotenoids lutein and zeaxanthin have also been found in green coffee (Degenhardt et al., 2006). Two glycosidically bound ionols (3-oxo-Gt-ionol and 3-oxo-7,8-dihydro-a-ionol) were identified in green coffee after enzymatic release from the isolated glycosidic mixture (Slaghenaufi et al., 2016). The major categories of sterols in coffee are 4-desmethylsterols (accounting for approximately 93% of total sterols), 4-methylsterols (2%) and 4,4-dimethyl-sterols (5%). Sitosterol belongs to the first category and accounts for up to 54% of the sterol fraction; stigmasterol and campesterol each account for approximately 20% (Speer and KölingSpeer, 2006). The average amount of total tocopherols in coffee has been reported as 11.9 mg/100 g green coffee (Ogawa et al., 1989) but varies considerably depending on the methodology used. The α, β and γ forms of tocopherols are present in coffee, with a predominance of β-tocopherol, followed by α and γ. Folstar et al. (1977) found concentrations of 8.9 to 18.8 mg α-tocopherol and 25 to 53 mg β- + γ-tocopherol/100 g coffee oil. Ogawa et al. (1989) reported the maximum total tocopherol content as 15.7 mg/100 g green coffee, with α-tocopherol accounting for 2.3 to 4.5 mg and β-tocopherol accounting for 3.2 to 11.4 mg/100 g green coffee; γ-tocopherol was not detected, possibly because of separation difficulty (Farah, 2012). Although most lipids are located in the endosperm of green coffee seeds, the coffee wax is located in the outer layer. This fraction accounts for 0.2 to 0.3% of the coffee seed’s weight. The main components of coffee wax are carboxylic acid-5-hydroxytryptamides, which are amides of serotonin and fatty acids of varying chain lengths (Speer and Köling-Speer, 2006).

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Chlorogenic acids comprise a major class of phenolic compounds which are derived primarily from esterification of trans-cinnamic acids (e.g., caffeic, ferulic and p-coumaric) with (−)-quinic acid. They are subdivided according to the nature and number of cinnamic substituents and the esterification position in the cyclohexane ring of the quinic acid (Clifford, 2000). The esters are formed preferentially with the hydroxyl located at carbon 5 as well as those located at carbons 3 and 4. Less commonly, esters may be formed with the hydroxyl located at carbon 1. The main subclasses of chlorogenic acids in green coffee are caffeoylquinic acids, dicaffeoylquinic acids, feruloylquinic acids and, less abundantly, p-coumaroylquinic acids and caffeoyl-feruloylquinic acids. Each of these subclasses consists of at least three major positional isomers in addition to minor compounds, with the exception of the latter class which contains six major isomers (Clifford, 2003; Farah et al., 2005; Farah, 2012). Among these classes, caffeoylquinic acids account for approximately 80% of the total chlorogenic acids content in the green seeds. Particularly, 5-caffeoylquinic acid (using IUPAC numbering system), the first of these compounds identified accounts for almost 60% and is therefore the most studied isomer and the first one for which a commercial standard was available. For this reason, 5-caffeoylquinic acid is commonly called chlorogenic acid. In the last decade, a series of minor chlorogenic acids and related compounds have been identified in green C. arabica and C. canephora seeds, including dicaffeoylquinic acids, acyl dicaffeoylquinic acids, dimethoxycinnamoylquinic acids, caffeoyl-dimethoxycinnamoylquinic acids, diferuloylquinic acids, feruloyldimethoxycinnamoylquinic acids, sinapoylquinic acids, sinapoyl-caffeoylquinic acids, sinapoyl-feruloylquinic acids, feruloylsinapoylquinic acids and new minor p-coumaric acid-containing compounds (Clifford et al., 2005, 2006; Perrone et al., 2008; Jaiwal et  al., 2010). Although these minor compounds together are not responsible for even 1% of total chlorogenic acids, studies are needed in order to investigate their role in coffee flavor. The content of chlorogenic acid in C. canephora is generally one and a half to two times higher than in C. arabica, but concentrations can vary significantly in both species. This higher content in Robusta coffee protects the coffee plant against diseases, insects and UV radiation (Farah and

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Donangelo, 2006). But although low amounts of chlorogenic acids are needed for flavor, high amounts may reduce cup quality possibly due to its own phenolic taste and oxidation products generated before roasting (Farah et  al., 2006). Differences in cell-wall composition between both species contribute to diverse chemical and physical responses to roasting. Astringency usually involves the association of polyphenols with proteins in the saliva to form precipitates (Fennema, 1996). As with other polyphenols, chlorogenic acids confer an astringent character to green coffee and much less in the roasted coffee brew. Their roasting derivatives contribute acidity and bitterness (and possibly sweetness) to the brew. Nevertheless, high amounts of some isomers in raw seeds may produce undesirable flavor both in raw and in roasted coffees probably due to oxidation and degradation products formed before roasting (Farah et al., 2006). Minor phenolic compounds such as anthocyanins, lignans and isoflavones have been identified in green seeds (Farah and Donangelo, 2006; Farah, 2017). The main compounds responsible for acidity in coffee are non-volatile organic acids, but low-molecular-mass organic acids also contribute to acidity as well as to the formation of aroma and the flavor of a coffee beverage due to their volatility. Organic acids contribute specific types and intensity of acidity in different ways, depending on the sensory characteristics, concentration in the beverage and also on their strengths. To date, about seven non-volatile aliphatic acids have been identified in green coffee (citric, malic, lactic, ascorbic, succinic, oxalic and tartaric acids), with the first four presenting larger contents. Additional acids present in the green seeds are quinic acid, which is the only alicyclic acid in coffee, small amounts of phenolic acids (caffeic, ferulic, p-coumaric), and phosphoric acid. Phosphoric acid is not organic but is included in this list because of its strength and importance to flavor (Farah and Lima, 2018). In the volatile fraction, acetic, butanoic, decanoic, formic, hexanoic, isovaleric and propanoic acids are also found in high concentrations in green coffee seeds (Pereira et al., 2018). The mineral composition of green coffee does not change during roasting and the original mineral profile of the seeds is an important

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element for setting the character of coffees. Potassium accounts for approximately 40% of total mineral content in ground coffee (approximately 1 to 2% of the total green coffee composition). The remaining mineral content consists of approximately 30 different elements, although about 50 minerals have been identified in various studies. In addition to potassium, major coffee elements include phosphorus, magnesium, calcium, sodium and sulfur (Clarke, 2003; Antonio et al., 2011; Pohl et al., 2013; Barbosa et al., 2014). Of these elements, only the magnesium content appears to vary considerably between species (1–3 mg/100 g for C. canephora and 2.5–6 mg/100 g for C. arabica) (Clarke, 2003). The profile of trace minerals in coffee, which includes zinc, strontium, silicon, manganese, iron, copper, barium, boron and aluminum, was reported to vary according to soil composition (Anderson and Smith, 2002). Table 9.1 summarizes the contents of the main compounds in the non-volatile fraction of raw coffee seeds. Table 9.1  Chemical Composition of Raw Coffea arabica and Coffea canephora Seeds CONCENTRATION (G/100 G DRY WEIGHT)a Carbohydrates/fiber components Oligosaccharides Reducing sugars: fructose, glucose, galactose, arabinose Polysaccharides Lignin Pectin Nitrogenous compounds Protein/peptides Free amino acids Caffeine Trigonelline Lipids Coffee oil (triglycerides with unsaponifiables, sterols/tocopherols) Diterpenes (free and esterified) Acids and esters Chlorogenic acids Aliphatic acids and quinic acid Minerals

Coffea arabica

Coffea canephora

6.0–11.0 0.1–0.5

3.0–7.0 0.4–0.5

34–44 3.0 2.0

48–55 3.0 2.0

8.5–12 0.2–0.8 0.9–1.3 0.6–1.2

8.5–12 0.2–1.0 1.5–2.5 0.3–0.9

15–18.0

7.0–12.0

0.5–1.2

0.2–0.8

6.7–9.2 2.0–2.9 3.0–5.4

6.1–12.1 1.0 3–5.4

Sources: Farah 2012; Poisson et al. 2017. a Content varies according to cultivar, edaphoclimatic conditions and methods of analysis.

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9.2.2 Volatile Composition of Raw C. arabica and C. canephora Seeds

The poor, volatile fraction of raw coffee seeds gives them a weak but characteristic aroma enjoyed mostly by coffee lovers and experts. The most abundant classes identified in green coffee seeds are alcohols, aldehydes, esters, hydrocarbons. Ketones, pyrazines, furans and sulfur compounds have also been identified (Flament, 2002; Toci and Farah, 2008). Only about 100 different volatile compounds have been identified in raw coffee seeds in past research (Flament, 2002), and this number has not increased significantly, since the highest variation in volatile coffee composition occurs during roasting and with many possible formation routes. However, with innovative postharvest fermentation methods, several new volatile compounds should soon be identified. During roasting, most volatile compounds in green seeds are degraded or modified, with some being potential precursors for new important volatile compounds (Dagenhardt et  al., 2006). On the other hand, microbial-derived, odor-active compounds produced during the removal of the fruit mucilage layer, including esters, higher alcohols, aldehydes and ketones, can still be detected in the final coffee product and affect cup quality (Pereira et al., 2018). 9.3 Roasting: Color and Flavor Development

The chemical processes leading to coffee flavor development and their relationships to the final character and perceived quality are not fully understood. However, the main chemical reactions that produce a number of changes in the non-volatile and volatile compositions of coffee and that develop its typical color and flavor are the Maillard reactions and caramelization, and in the latter stages, pyrolysis. Maillard reactions are a set of reactions occurring generally from about 130 to 200°C, between an amino group of an amino acid, peptide or protein and a carbonyl group of a reducing sugar such as fructose, glucose, galactose maltose and so forth, to ultimately form brown melanoidins of varied molecular weights. Additionally, different sugars and amino acids produce a number of molecules which react and interact further with other compounds. Therefore, both volatile (such as furans, pyrazines, pyridines) and non-volatile compounds are created in these reactions, which are dependent on a few

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variables namely the different amino acids available, amount of water, the presence of salts, temperature, pH and the period of time held at a certain temperature. The Maillard reactions include the Strecker degradation, which involves the reaction of two carbonyl groups of amino acids and creates ketones, often with buttery and caramel flavors (Fenemma, 1996; Nursten, 2007). Caramelization is a non-enzymatic complex set of browning reactions that occur exclusively with sugars. It includes inversion (of sucrose to glucose and fructose), condensation reactions, intramolecular bonding, isomerization, dehydration, fragmentation reactions and polymerization. These pyrolitic reactions are slower than Maillard reactions and require higher temperatures (about 160 to 200°C). As part of the caramelization process, sugar is converted to furfuryl that has a caramel-like, slightly burned note and also slightly meaty note. The same compound is produced via a different route in the Maillard reactions. As temperatures get higher, a number of additional compounds with different molecular masses are formed. In model caramelization, a sugar solution will initially be sweet, with no aroma. Through caramelization, it becomes both sour and a little bitter, as a rich aroma develops. Generally, the longer sugar is caramelized, the less sweet it tastes (Fenemma, 1996; Clarke, 2003; Nursten, 2007). Pyrolysis often refers to the degradation reactions caused by heat, but pyrolysis per se actually refers to the thermal decomposition of organic materials at elevated temperatures (200–300°C) in an inert atmosphere producing compounds with low molecular masses, mostly volatile products, leaving a carbon-enriched residue, with burned sensory notes. 9.3.1 Color Development

The temperatures set inside the roasting chamber depend on the roaster type and roast profile, but allowing for variations maximum temperatures used in industrial fluidized-bed roasters generally range from 200 to 240°C. Roasting at very low temperatures will “bake” the seeds rather than roast them but very high temperatures will not allow proper flavor development and produce a thin-bodied brew. The various existing descriptions of the physical and chemical changes that occur during roasting can be contrasting, especially in respect

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to temperatures in which the events occur, possibly due to referrals to roasting chamber temperature and seeds’ temperature in the different reports, which are not the same all the way in the process. A simplified description of such changes, including color development, follows. In the initial phase of the process, as the seeds temperature raises, the internal pressure also raises, causing unbound water redistribution and evaporation. Chemical changes in this initial phase are relatively small compared to those that occur later in the process. Roasting per se begins at temperatures above 160°C, when a series of exothermic and endothermic reactions begin to take place (Clarke, 2003). At this point, Maillard reactions and caramelization have initiated, but the seeds are still light brown. When bound water evaporates, it forces the seeds to swell producing a series of cracking sounds known as “the first crack.” At about 190°C, low- and high-molecular-weight compounds such as brown melanoidins are simultaneously produced and degraded in the Maillard reactions. Not long after this point, the seeds are brown (milk chocolate color or medium roast), and aroma formation reaches its peak (Czech et  al., 2016). As roasting progresses, carbon dioxide is released causing considerable seed expansion and making “the second crack,” when the seeds achieve a dark chocolate color and the oil starts to come to the seed’s surface. From about 200°C on, pyrolysis takes place, and the seed darkens rapidly until it becomes black (Clarke, 2003). These reactions can be interrupted at the desired point, and the seed is immediately quenched by just a little sprayed water or cool air, which is preferred if water does not evaporate completely, and it increases the risk of microbial growth and quality deterioration. When roasting is over, coffee color is referred to as a roast degree, which most commonly varies from light-medium to dark, according to national and individual preferences. In the UK and United States, for example, light-medium to medium roasts which tend to be fruity and sweet, respectively, are preferred, whereas dark roasts, which present more body and bitterness, are more popular in some parts of Europe. Dark-medium to dark roasts are traditional in Brazil, although the consumption of medium roasted coffees has been increasing because of the dissemination of the health advantages of this roast. Roast degree standards for commercial and scientific purposes are subjective

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and may vary considerably. The loss of mass during roasting may be a useful parameter for evaluating the roasting degree in small-scale production (Farah et  al., 2005), but it could be difficult to control in large-scale production. Visual inspection continues to be the most accepted method for determining the degree of roasting. Currently, there are many different coffee color meters available for industrial and lab use purposes. Additionally, to help develop standards for colorimetric assessment, color disks have been created by the Specialty Coffee Association of America (SCAA), which, currently, after merging with the Specialty Coffee Association of Europe, is known as SCA. The disk scale is named AGTRON/SCAA Roast Classification Colour Disc System, and it can be used to classify most commercially available coffees. The color palette is based on the linear progression of color development obtained under controlled roasting conditions (Farah, 2012). It is advisable that green seeds have a standard size and color so that roasting occurs homogeneously. Broken, small seeds and defects can get burned during roasting, and some pale seeds called quakers maintain the underdeveloped color and stand out among the brown seeds. Quakers are detrimental to the cup and often with a stinky aroma. The causes for this defect are still debatable, but one possible reason would be incomplete development of the fruit and low amount of carbohydrates in the green seeds and, consequently, problems in the Maillard and caramelization reactions. Another related hypothesis is a higher amount of protein associated with increased sucrose degradation during roasting (Mazzafera et al., 2018). 9.3.2 Chemical Changes and Flavor Development

The chemical profile of raw seeds dramatically changes during roasting. Some compounds are degraded and others are formed, including substances of high, medium and low molecular masses. The variety and concentrations of these volatile and non-volatile compounds depend on the composition of the precursors in the raw seeds and on the roasting conditions such as roaster type, roast profile and roasting degree. Most of the aroma compounds show the highest formation rate at medium roast degree and decrease thereafter. The main changes in coffee chemical profile during roasting are discussed below.

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Dehydration is one of the first reactions that occur during coffee roasting. The water content of roasted coffee decreases from about 50 to 85% depending on the roast degree, to about 2 to 7%. The darker the seeds, the lower the moisture content will be. The dehydration kinetics depends on the roast profile. Sucrose is first degraded to glucose and fructose and then mostly (about 98%) consumed by caramelization and Maillard reactions, in addition to being partly converted to a variety of organic acids. Oligosaccharides, polysaccharides (galactomannans and arabinogalactan-proteins) and other carbohydrates are also partly converted to organic acids, producing acidity, partly incorporated into melanoidins, producing color (Bekedam et  al., 2008) and partly solubilized. These melanoidin polymers exhibit variable composition and a molecular mass approximately 25% of its dry weight (Nicoli et al., 1997). Carbohydrates are responsible for the production of furans, aldehydes, ketones and phenols (Flament, 2002). A portion of the coffee protein is degraded, free amino acids and peptides are consumed by Strecker reactions. Some of the amino acids react with reducing sugars to form low-molecular-weight compounds and melanoidins (Bekedam et  al., 2008). The remaining free amino acids (phe, tyr, arg, leu, iso, val, met, his) may contribute bitterness to the beverage; free asparagine contributes an umami taste. Protein peptides and amino acids produce ketones, pyrrols and pyrazines (Flament, 2002). Roasting degrades trigonelline as it progresses, producing a variety of pyridinium derivatives, including nicotinic acid (about 3%, via demethylation), methylpyridinium compounds and volatiles such as pyrroles (about 3%), pyridines (about 46%), pyrazines and methyl nicotinate (Trugo and Macrae, 1984; Flament, 2002). Trigonelline contributes bitterness to the brew, and nicotinic acid has a slightly acidic or sour taste. According to Flament (2002), some pyrroles and pyridines may confer an “objectionable” flavor. Caffeine is not significantly changed during coffee roasting, but small losses may occur due to sublimation, although a relative increase in caffeine content may be observed due to the loss of other compounds. Despite its bitter nature, it is reported to be responsible for no more than 10 to 20% of the perceived bitterness of the coffee beverage (Flament, 2002).

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The presence of different acids and their content in green seeds are not necessarily indicators of the acids profile nor the quality of roasted seeds. The role of roasting and brewing is pivotal in flavor and cup quality development. During roasting, part of the alicyclic and aliphatic acids existing in green coffee is degraded, but despite this partial loss, additional acids are generated from carbohydrates in the initial phase of the process. For example, part of the malic acid may form fumaric and maleic acids, while the content of citric acid may remain intact or be degraded to form citraconic, glutaric, itaconic, mesaconic and succinic acids. Ascorbic acid is also degraded in the process. At the beginning of roasting, the brew’s acidity tends to increase as levels of aliphatic acids rise. Formic and acetic acids’ yields increase up to a medium roast degree and then begin to fall as the process continues. The formation of these acids is considered a key factor related to the higher acidity and lower pH obtained at light to medium roasts compared to dark roasts. In total, about 18 aliphatic acids have been identified in roasted coffee seeds and beverages, including residual acids from green seeds and newly formed acids during roasting. They are ascorbic, citric, citraconic, formic, fumaric, glycolic, isocolic, lactic, maleic, malic, mesaconic, oxalic, propionic, succinic, tartaric and pyroglutamic acids. (Farah and Lima, 2018). Quinic acid is an alicyclic acid and chlorogenic acids are in fact a large family of esters. Therefore, these are not included in the list. Like other polyphenols, chlorogenic acids produce astringency in the mouth, which may contribute positively to coffee’s flavor when in low concentration. Because of thermal instability, chlorogenic acids undergo many changes during roasting, namely isomerization, epimerization, lactonization, decarboxylation and degradation to low-molecular-weight compounds. When in high amounts, in green seeds, caffeoylquinic and feruloylquinic acids may produce an undesirable flavor after roasting possibly due to oxidation and degradation products formed in raw seeds which are evidenced by their dark color (Farah et al., 2006). Chlorogenic acid lactones or quinides contribute considerably to the positive bitterness of the coffee beverage, an important aspect of quality. They are formed by less than 10% of total chlorogenic acids in green coffee through loss of a water molecule from the quinic acid moiety and formation of an intramolecular ester bond.

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Considering that the caffeoylquinic acids are the major lactones precursors in coffee, the main chlorogenic acids lactones formed during roasting are the 1,5-γ-lactones, with 3-caffeoyl-1,5-quinide and 4-caffeoyl-1,5-quinide being major lactones. The formation of feruloy1,5-quinides, coumaroyl-1,5-quinides and one dicaffeoyl-1,5-quinide (Farah et al., 2005; Czech et al., 2016), as well as minor δ-lactones (Sholzand Maier, 1990) have also been reported. Lower-molecular compounds produced from chlorogenic acids degradation include caffeic (bitter), ferulic and quinic acids, cathecols, including vinylcatechol, ethylcatechol, 4-vinylguaiacol (positive sensory notes of spice, clove), guaiacol (phenolic, smoky, spice, vanilla, woody, but sometimes medicinal notes), pyrogallol, 4-vinyl1,2-benzenediol, vanillin (derived from ferulic acid, is important for coffee aroma) and phenol. Such derivatives may confer pleasant or unpleasant sensory notes, depending on the compound and concentration, tending toward an unpleasant note as their concentrations rise. Among additional bitter compounds identified in the caffeic acid derived fraction with low recognition threshold concentrations are 1,3-bis(3ʹ,4ʹ-dihydroxyphenyl) butane, trans-1,3bis(3ʹ,4ʹ-dihydroxyphenyl)-1-butene and eight multiply hydroxylated phenylindanes produced by the oligomerization of 4-vinylcatechol. They yield a lingering, harsh type of bitter sensation typical of overroasted coffee. As previously mentioned, chrologenic acid products are also incorporated into melanoidins, contributing to color development. In any case, chlorogenic acids do not contribute to the brew’s acidity as importantly as the sum of aliphatic acids and phosphoric acid (Trugo, 2003; Frank et al., 2007; Czech et al., 2016; Farah and Lima, 2018). Chlorogenic acid degradation follows first-order Arrheniuscompliant kinetics; however, distinct models should be used for C. arabica and C. canephora samples (Perrone et al., 2010). Depending on the roasting degree, the total chlorogenic acid content may be reduced to less than 1% of the original content. Reports on chlorogenic acid content in commercial roasted coffees vary from about 0.5–6 g/100 g considering both C. arabica and C. canephora species, dry weight, depending on the type of processing, blend, roasting degree and roasting method (Farah and Donangelo, 2006; Duarte and Farah, 2009; Farah, 2012).

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The lipid fraction including triacylglycerols and sterols is relatively heat stable. Although diterpenes are more sensitive to heat, reasonable amounts (0.2–0.9 g/100 g dry weight) may still be found in roasted coffee especially in C. arabica. Tocopherol content also decreases during roasting. Depending on the roast degree, α-tocopherol, β-tocopherol and total tocopherols may be reduced 79 to 100%, 84 to 100% and 83 to 99%, respectively (Speer and Kölling-Speer, 2006; Farah, 2012). Generally speaking, lipids are responsible for the production of small amounts of aldehydes and ketones. Roasting models revealed that carotenoids are precursors of β-damascenone (sweet rose-like notes) and β-ionone (floral notes), very potent aroma compounds with a very low odor threshold (Simkin et al., 2004; Degenhardt et al., 2006). Also in model roasting, β-damascenone and ionols may give rise to megastigmatrienone isomers reported as potential contributors to tobacco notes in spirits in general and spice notes in wine (Degenhardt et al., 2006; Slaghenaufi et al., 2016). Table 9.2 summarizes the non-volatile chemical composition of roasted C. arabica and C. canephora seeds. After roasting, the classes of volatile compounds typically found in roasted coffees are furans and pyrans, pyrazines, pyrroles, ketones, phenols, hydrocarbons, alcohols, aldehydes, acids and anhydrides, esters, lactones, pyridines, amines, thiophenes, oxazoles, thiazoles, imidazoles and various sulfur and nitrogen compounds (Blank et al., 1991; Flament, 2002; Yeretzian, 2003). It is difficult to determine all the reactions that generate these volatile compounds since a number of them may be produced by more than one route. The classical correspondence between the precursor and volatile products has been mentioned previously. The link between flavor components and the sensory properties expressed in the complex coffee matrix is yet to be fully understood, but despite a large number of volatile compounds identified in roasted coffee to date less than 100 compounds have a strong odorant power and have been reported to impact coffee aroma. Nevertheless, the odor impact of isolated compounds is different from when they are assembled with other compounds with high, medium or low odorant activities in the coffee matrix. Therefore, the presence of other volatile components in the matrix matters. Moreover, the singular arrangements among coffee typical aroma components as well as the addition of extra volatile components help create the distinction between the different flavors.

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Table 9.2  Summary of the Non-Volatile Composition of Roasted Coffea arabica and Coffea canephora Seeds CONCENTRATION (G/100 G DRY WEIGHT)a Carbohydrates/fiber components Sucrose Reducing sugars Polysaccharides Lignin Pectins Nitrogenous compounds Protein/peptides Free amino acids Caffeine Trigonelline Nicotinic acid Other pyridinium compounds Lipids Coffee oil (triglycerides with unsaponifiables) Diterpenes (free and esterified) Minerals Acids and esters Chlorogenic acids Aliphatic acids Quinic acid Melanoidins

Coffea arabica

Coffea canephora

4.2–tr 0.3 31–38 3.0 2.0

1.6–tr 0.3 37–42 3.0 2.0

7.5–10 0.0 1.1–1.3 1.2–0.2 0.02–0.03 0.07–0.3

7.5–10 0.0 2.4–2.5 0.7–0.3 0.01–0.03 –

17.0 0.9 4.5

11.0 0.2 4.7

1.9–2.5 1.6 0.8 25.0

3.3–3.8 1.6 1.0 25.0

Sources: Clifford 2000; Farah, 2012; Farah et al., 2017; Poisson et al. 2017; Trugo, 2003; Kölling-Speer and Speer, 2005; Speer and Kölling-Speer, 2006. a Content varies according to cultivar, edaphoclimatic conditions, methods of analysis and roasting degree.

The seeds of C. arabica and C. canephora species have a different profile of precursor compounds, and therefore it is not surprising that they also exhibit different volatile profiles, resulting in markedly distinct aromas. Blank et  al. (1991) reported that caramel-like and sweet-roasty attributes predominate in C. arabica, whereas spicy and earthy-roasty attributes prevail in C. canephora species. Examples of predominant volatiles that contribute to these dominant notes are 3-mercapto-3-methylbutylformate, sotolon, abhexon, 2-methyl-3-furanthiol, phenylacetaldehyde, 3,4-dimethyl-2-cyclopentenol-l-one, 2-/3-methylbutanoic acid and linalool in C. arabica seeds. Whereas in C. canephora seeds, 2,3-diethyl-5-methylpyrazine, 4-ethylguaiacol

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and 3-methyl-2-buten-l-thio are more abundant. Table 9.3 contains important impact compounds for coffee aroma and the main reported odor characters. It is noteworthy, that at times odor and flavor sensations may be slightly different. 9.4 Roast Profile and Flavor

The heat transfer rate and consequently the chemical reactions that occur during roasting depend on the roasting method applied. The type and size of a roaster along with the amount of coffee per batch can vary considerably, and so different roast parameters must be established for each type of roaster and adapted for various types and amounts of coffee. Such parameters may include roasting chamber temperature, seed temperature, air stream temperature and speed of circulation (in the case of fluidized or spouted bed roasters), roasting time and so forth. Regardless of the differences in roasting technologies, these parameters must be applied with the aim of producing the desired seed’s temperature needed to cause certain chemical reactions for as long as desired. Programming the change of these parameters to produce a controlled rise, hold and decrease in seed temperature is called a roast profile. Therefore, two coffee samples from one lot can be roasted to reach the same color under different roasting conditions and present distinct chemical compositions and cup results. An expertly programmed roast profile can fully explore the seeds’ flavor potential. These findings derive from experienced roasters’ and cuppers’ empirical observations. Experienced roasters know when to use different parameters to increase or decrease flavor attributes. Even though they might not be fully aware of the chemical changes occurring in the seeds, they are able to improve the quality of a coffee batch by using the proper roast profile. For example, while the fast rise of temperature at the beginning of the process may produce strong roasty flavor, slow rising often increases attributes like balance, fruity, nutlike and toasty notes. It is worth mentioning that fast roasting at very high temperatures may also over-roast the seed externally and underroast the seeds internally, leading to burned and greenish defective notes at the same time (Schenker and Rothgeb, 2017).

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Table 9.3  Impact Compounds in Coffee Aroma and Their Main Odor Attributes KEY ODORANT COMPOUND 2-Methylbutyric acid 3-Methylbutyric acid Propanal Hexanal Acetaldehyde p-Anisaldehyde Methylpropanal 2-Methylpropanal 3-Methylpropanal 2-Methylbutanal 3-Methylbutanal 4-Methylbutanal Methional (E)-2-Nonenal Phenylacetaldehyde 4-Methoxybeanzaldehyde 2-(Methylthiol)propanal Ethyl-2-methylbutyrate Ethyl-3-methylbutyrate Furfural Furfuryl formate Furfurylmethyl ester 5-Methyl-2-furancarboxyaldehyde Furfuryldisulfide 2-Methylfuran 2-Furanmethanol acetate/ furfurylacetate 2-[(Methylthio)methyl]furan Methanethiol 3-Methyl-2-butene-1-thiol 4-Methyl-2-butene-1-thiol 2-Methyl-3-furanthiol 2-Methyl-4-furanthiol Dimethyl sulfide Dimethyl disulfide Dimethyltrisulfide 2-Furfurylmercaptane

AROMA DESCRIPTION Acidic, fruity, dirty, cheese, sweaty Acidic, sour, pungent, fruity, stinky, sweaty Ethereal, pungent, earthy, alcoholic, roasted, fruity Floral Fruity, pungent, ethereal, fresh, lifting, penetrating, musty Minty Flora, spicy Buttery, oily, malty, fruity, tasty, caprylic, cheesy, dark chocolate Roasted cocoa Malty, green, solvent, buttery, rancid, almond, toasty Malty, cocoa, fruity, almond, tasty, ethereal, chocolaty, peachy, fatty Buttery Baked potato Buttery, fatty, green, cucumber, citrus Sweet, fruity, honey, floral, fermented Sweet, powdery, vanilla, anize, woody, coumarin, creamy Soy sauce Fruity, berry Fruity Almond, bread, sweet, caramel, woody, brown Ethereal Roasted coffee Sweet, caramel, bready, brown, coffee Sulfurous, coffee, roasted chicken, meaty, onion, cabbage Burned, ethereal (mild), gasoline, acetone, chocolate Onion, garlic, sulfurous, pungent, horseradish Smoke, roast, onion, garlic, sulfurous, horseradish, vegetable, pungent Baked potato, sulfur, garlic, pungent, cabbage, meat/fish, rotten eggs (putrid in increased concentrations) Sulfurous, smoky, leek, onion Tobacco, roasted Sulfurous, meaty, fishy, metallic, boiled Meat Sulfur, cabbage Sulfur, cabbage Sulfur, cabbage Sulfury, roasty (Continued )

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Table 9.3 (Continued)  Impact Compounds in Coffee Aroma and Their Main Odor Attributes KEY ODORANT COMPOUND 2-Furfurylthiol Furaneol 3-Mercapto-3-methylbutylacetate 3-Mercapto-3-methylbutanol 3- Mercapto-3-methylbutyl formate 2-Furanmethanthiol 2-(Methylthio-methyl)furan 3-(Methyltio)propionaldehyde (methional) 3,5-Dihydro-4(2H)-thiophenone 2-Acetyl-2-tyazoline 4-Methylbutanoic 4,5-Dihydro-2-methyl-3(2H) furanone 4-Hydroxy-2,5-dimethyl-4(2H)furanone (furaneol) 2-Ethyl-furaneol 3-Hydroxy-4,5-dimethyl-2(5H)furanone (sotolon) 5-Ethyl-4-hydroxy-4-methyl-2(5H)furanone (abexon) 2-Ethyl-4-hydroxy-5-methyl-4(5H)furanone 3- Methyl-2-buten-1-thiol 2,3-Butanedione 2,3-Pentanedione 1-Octen-3-one 2-Hydroxy-3-methyl-2-ciclopentene1-one β-Damascenone 2-Methoxyphenol 4-Methoxyphenol 4-Ethyl-2-methoxyphenol 4-Vinyl-2-methoxyphenol 4-Ethenyl-2-methoxyphenol 3-Methylindole 4-Hydroxy-3-methoxybenzaldehyde (Vanilline) 2-methoxyphenol (Guaiacol) 2,3-Dimethylpyrazine 2,5-Dimethylpyrazine

AROMA DESCRIPTION Roasted (coffee), sulfurous Sweet, caramel Roasty, fruity, sulfurous, sweet Nutty/roasted Catty, blackcurrant like, herbal, fruity, roasted, sweaty Smoke, roasted Tobacco, roasted Potato Tobacco, roasted Roasted Sweet, acidic Sweet, bready, buttery, nutty Caramel, sweet Caramel Fenugreek, curry, sweet caramel Spicy, caramel Sweet, caramel Sulfurous Buttery Oily-buttery Mushroom Sweet, caramel Floral, cooked apple, fruity, sweet, honey Phenolic, burned Phenolic, smoky Phenolic, spicy, clove Spicy, clove Phenolic Coconut Vanilla Smoky, spicy Nutty, roasted Nutty, roasted (Continued )

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Table 9.3 (Continued)  Impact Compounds in Coffee Aroma and Their Main Odor Attributes KEY ODORANT COMPOUND 2-Ethylpyrazine 2-Ethyl-6-methylpyrazine 2,3-Diethyl-5-methylpyrazine 2-Ethyl-3,5-dimethylpyrazine 3-Ethyl-2,5-dimethylpyrazine 2-Methoxy-3,5-dimethylpyrazine 2-Methoxy-3,2-methylpropylpyrazine 2-Methoxy-3-isopropylpyrazine 3-Isopropyl-2-methoxypyrazine 3-Isobutyl-2-methoxypyrazine 3-Isobutyl-3-methoxypyrazine 2-Ethenyl-3,5-dimethylpyrazine 2-Ethenyl-3-ethyl-5-methylpyrazine 2-Metoxy-3-isobutylpyrazine 6,7-Dihydro-5H-ciclopentapyrazine 6,7-Dihydro-5-methyl-5Hciclopentapyrazine 3-Mercapto-3-methylbutyl formate 3,7-Dimetil-octa-1,6-dien-3-ol (Linalool) 1-Methyl-4-(1-methylethenyl)cyclohexene (Limonene) 3,7-Dimethyl-2,6-octadien-1-ol (Geraniol)

AROMA DESCRIPTION Nutty, buttery, peanut, chocolate Potato, Nutty Earthy, roasted, nutty Earthy, nutty, coffee, caramel, cocoa Earthy, roasty Earthy Green, earthy Earthy, roasty Earthy Earthy, pea Earthy Earthy, roasty Earthy Earthy, pea Nutty, roasted Nutty, roasted Catty/roasted/blueberry/herbal Floral Citric, lemon Floral

Source: Czerny, M. and W. Grosch. 2000. Journal of Agricultural and Food Chemistry 48 (3): 868–872; Maeztu et  al., 2001; Sanz et  al., 2002; Blank et  al., 2002; Kumazawa and Masuda, 2003; Akiyama et al., 2005; Poisson et al., 2017; Yeretzian, 2017. Note: In general, furans have lower odorant power, but they are abundant in coffee.

Since the possibility of changing roasting parameters during the process and creating different profiles is relatively new, there are not many scientific reports available illustrating such differences. The roast profile seems to interfere in the formation and degradation of acids and in the titratable acidity, but to date there is no clear correlation between these factors, possibly because of differences within the categories of fast and slow roast profiles. Wang and Lim (2012) and Santos et al. (2016) obtained maximum titratable acidity at lower roasting temperatures (about 200–210°C). However, other studies have reported that coffees roasted at higher temperatures for shorter periods of time exhibited higher acidity due to higher levels of

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aliphatic acids such as formic, acetic, glycolic and lactic acids (Ginz and Balzer, 2000; Toci et al., 2009). Fast roasting also reduced the loss of the esters chlorogenic acids and trigonelline compared to slow roasting and resulted in more soluble solids (Toci et al., 2009). Additionally, differences in volatile profiles were observed. Examples of volatile compounds whose concentrations have been affected by changes in roast profiles are pyridine (at very low concentrations present coffee and chocolate notes but at high concentrations fish and putrid odor), 2-methylpyrazin (nutty, cocoa, musty, green, roasted odor), furfural (sweet, brown, bready, caramellic), 5-methyl-furancarbaldehyde (caramelic, brown), furfuryl formate (ethereal odor), 2-furanomethanol acetate (floral rose, fruity, sweet, honey, tropical odor), 1-(2-furanylmethyl)-1H-pyrrol (coffee, vegetable, fruity, mushroom odor), 1-(1H-pyrrol-2-yl)-ethanone (or 2-acethyl pirrole, with musty odor), 2-methoxyphenol and 4-ethyl-2-metoxyphenol (or ortoguaiacol and 4-ethyl-guaiacol, respectively, with phenolic, smoky, spicy, vanilla, woody attributes) (Toci et al, 2009; unpublished data of author’s own research). In another study, medium and fast roasting speeds favored ketones formation, while slow roasting speed favored pyridines formation (Petisca et al., 2013). It is worth noting again here that the same odorant compounds may impact coffee aroma differently, depending on their odorant power and concentration, revealing pleasant or unpleasant and aggressive notes and therefore changes caused on these compounds by the roast profile may affect the final cup. Because of the individual characters of the seeds which may demand different roast profiles, blending should be done preferably after coffee is roasted. Blending is usually performed to balance flavor and create a better final result or to decrease costs although keeping quality. As for grapes and wines, due to the potential fluctuation in coffee flavor among distinct crops in a given farm, new blending recipes might be needed seasonally, according to the character of coffee crops, budget and costs. 9.5 Generation of Flavor Character and Off-Flavors

In addition to the genetic traits and roast profiles previously discussed in this chapter, there are other factors that can change raw coffee seeds

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chemical composition and physical aspects and consequently affect the flavor after roasting, imparting a specific (positive) character to the brew or ruining it with off-flavors. For example, terroir, agricultural practices, fruit maturation degree/harvest, postharvest processing and storage conditions prior to roasting (Farah and Donangelo, 2006). They will be briefly discussed below. The character of coffees within the same species and cultivar can vary considerably when grown in different terroirs. Among factors that contribute to the character inherent to a terroir are the geographic location (latitude, longitude and altitude) and consequently macro and microclimate, rainfall and humidity, soil type (composition and drainage characteristics) and microbiome, topography (which affects wind, etc.). The terroir microbiome is important because specific microorganisms can act on the seeds components during postharvest processing producing volatile and non-volatile components that will give them a specific character or signature after roasting. Therefore, two plants of the same species and cultivars grown in different terroirs and under the same agricultural practices may have completely distinct cup results. But what happens in reality is that specific cultivars are chosen to fit a certain terroir due to higher productivity and/or higher quality under those edaphoclimatic conditions. Additionally, agricultural practices also have to be adapted. The acknowledgment of terroirs made the creation of coffee origin certificates possible in most producing countries to aggregate value to their special characters. Due to a large number of variables simultaneously involved in a given terroir, conclusive studies associating the typical sensory character of a given terroir to the seeds chemical composition are scarce, but since coffee mineral composition varies with soil composition, some studies have succeeded in differentiating coffees from different origins by their mineral profile (especially trace elements) (Anderson and Smith, 2002). The fatty acid profiles, especially oleic, linoleic and linolenic acids were also reported to strongly contribute to the discrimination of the environment in a specific town in the State of Minas Gerais, Brazil (Figueiredo et al., 2015). The fruit maturation degree is a very important aspect that contributes to significant differences in coffee chemical composition and consequently flavor. Harvesting fruits that are in different maturation stages from cherry (ripe) fruits generate defective seeds or defects. For

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example, immature fruits give green defects with notable astringency due to the higher amount of phenolic compounds. They also contribute green, grassy off-notes to the beverage and produce lower amounts of pleasant volatile compounds (aldehydes, ketones and higher alcohols) in comparison to those from cherry fruits. Brown seeds from fermented ripe or overripe fruits (often found on the ground) are called sour defects and present fermented and sour notes. Black seeds from overripe fruits are called black defects with off-notes of tobacco smoke and burned. Overripe fruits are often contaminated with microorganisms, and therefore earthy, fermented and other off-notes are commonly observed in these seeds (Toci and Farah, 2008, 2014; Dias et al., 2012). In general, such defects produce very objectionable sensory notes in the brew which are particularly noted in the case of specialty coffees, in which the presence of one defect can decrease the cup score considerably. Such defective seeds, as well as a number of additional defects, are not expected to be present in commercial coffee blends, but for economical reasons they often are. So scientists have tried to find chemical compounds that can not only explain their off-flavors but also serve as markers for their presence in roasted blends. In seeds exhibiting the Rio off-flavor (earthy, medicinal), common in humid Brazilian areas, 2-methyl-isobutanol, 2,4,6-tricloroanisol, geosmin and the pyrazines 2-methoxy-3-isopropylpyrazine and 2-metyoxy-3-isobutylpyrazine have been identified as markers for this specific off-flavor (Spadone, 1990; Cantergiani et  al., 1999; Bortoli and Fabian, 2001). Later, the comparison of regular and defective coffee seeds (from the same lot) originated in various producing areas of Brazil identified the following compounds exclusively found in ground-roasted defective seeds such as 2,3,5-trimethyl-6-ethyl-pyrazine (immature seeds and others), 3,5-dimethyl-2-butylpyrazine (black-green, sour), butyrolactone and hexanoic acid (sour and black) and 2,3,5-trimethylpyrazine (shell core). Other compounds were not exclusive but were present in a higher concentration in roasted defective seeds. Among them were isoamyl-6-methylpyrazine (sour), 3-methyl2-butylpyrazine (sour), 2,3 butanediol meso, 4-ethylguaiacol, 3-methylpiperidine (black), 2-pentyl-piperidine, 3-methyl-piperidine and 2-propyl-piperidine (black) and 3,7-dimethyl-1,6-octadien3-ol (β-linalool) (sour) (Toci and Farah, 2008; Toci et  al., 2009).

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Again,  several of these compounds, as well as other marker compounds identified in raw defective seeds, are typically associated with fermentation by molds and bacteria and with oxidation processes. In addition, some volatile compounds may produce pleasant aroma attributes at low concentrations in good quality seeds but can be intolerable at high concentrations, which usually happens in defective or low-quality seeds (Toci and Farah, 2014). For example, some biogenic amines, pyrazines and phenol derivatives are common in defective seeds and when in high concentrations, are known to produce objectionable flavors (Flament, 2002; Oliveira et al., 2005; Toci and Farah, 2008; Toci et al., 2009). Furthermore, higher and lower quality seeds exhibit distinct behaviors during roasting under different roast profiles, producing different cup results. Compounds that were shown to be affected by the quality of raw seeds and roasting conditions included 2-methylpyrazine, 2,3,5-trimethylpyrazine, 1H-pyrrole and 2-furfurylmethanol. In addition to differences in non-volatile and volatile precursors in regular and defective green seeds, the cell walls of both types of seeds contain different amounts of cellulose, lignin and hemicelluloses, which may affect heat transfer from outside to inside, accelerating or retarding the roasting process. This is one of the reasons why different types of coffee seeds, including age aspect, should be roasted separately and blended later on. Postharvest processing methods change the seed’s chemical composition and consequently their sensory characteristics after roasting. In fact, this step is vital in governing the final result in the cup. Traditionally, there are two types of methods, namely the dry and wet methods. In the traditional dry method, harvested fruits are exposed to sun and/or air dryers until the moisture content reaches about 10–12% and thereafter the fruits are stored. Then, they are cleaned and dehusked (hulled), with the full removal of dried skin and pulp, leaving a thin mucilaginous tissue (silver skin) adhering to the seed’s surface. The silverskin is rich in polysaccharides in addition to other compounds. These types of seeds often play a part in espresso coffee blends, since they provide body to the brews. Coffees processed by this method are marketed as natural coffees. As the dry method has traditionally been used to dry fruits that are not selectively harvested (they are harvested by stripping the plant branches or by machinery),

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it is believed to generate inferior quality seeds, but when used for coffee cherries, the seeds tend to be sweeter, chocolaty, aromatic and with caramel notes. The wet processing is more complex and laborious than dry processing and can also produce aromatic and flavorful brews, given the process is well executed. This process is less time consuming (about a third compared to dry processing), and the area required for drying the seeds is smaller. Cherry selection takes place in flotation tanks, and then the fruits are partly pulped, leaving the inner pulp layer (often called mucilage) in addition to the silverskin on the seed. This is followed by soaking for fermentation. During fermentation, enzymes, selected microorganisms or natural microbiota may be used to remove mucilage and most of the silverskin. Frequently, yeast species used during coffee processing are Saccharomyces cerevisiae, Pichia kluyveri, Pichia anomala, Hanseniaspora uvarum, Debaryomyces hansenii and Torulaspora delbrueckii. In addition to Saccharomyces sp., Pichia fermentans and Lactobacillus plantarum have been suggested as starter cultures in Brazil (Neto et  al., 2017). During fermentation, acidity increases and flavor develops and the pH may reduce to 4.5. The seeds are then thoroughly washed, polished and sun and/or air dried. Coffees treated by this method are called washed or pulped coffees. A third, hybrid method was created in Brazil, in which fruits are washed, selected in flotation tanks, and partly pulped before drying, leaving the mucilage on the seeds like in the wet method, until the seeds are dried for mild natural fermentation under the sun and later hulling. Coffees processed this way are called pulped naturals. A variation of it is the “honey coffee,” which involves slow drying (about a week or so, depending on the amount of mucilage left on the seeds) in suspended beds and controlled mucilage fermentation to enrich flavor, avoiding mold development. It is called honey because, since the seeds maintain the mucilage before drying, they get sticky. Currently, there are black, red and yellow honey coffees, and the color depends mostly on the initial sugar content on the pulp or mucilage. This process is performed on cherry (ripe) fruits only and most often results in sweet, fruity, aromatic, specialty coffees, with a balanced acidity. In the last decade, when producers realized how important this production step is for increasing (or ruining) coffee quality and aggregate value, these methods have been improved by applying simple but

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effective technologies for specialty coffee production. Additionally, with the “Third Wave” movement in which consumers search for new flavor experiences from their cup of coffee, a number of variations in postharvest processing are being created (some of them resembling wine production) to elicit such experiences. In these seeds, different types of controlled fermentation have been practiced for exploring the potential of varietals (especially the sweeter yellow varietals), enhancing their natural aroma and balancing their acidity and sweetness, or imparting more floral aromatic notes to them. As mentioned, natural fermentations are usually performed using yeasts associated or not with other microorganisms. They break down simple and complex carbohydrates, phenolic compounds and other components present in coffee mucilage, producing reducing sugars, organic acids (lactic, acetic, succinic, among others) and lower molecular size compounds (aromatic acids, ketones, aldehydes and aliphatic esters) that cause positive changes in flavor development during roasting (Neto et al., 2017). Although such dry fermentations help to promote sweet, chocolate and fruity characters out of coffee, the temperature which affects the rate of fermentation and time must be thoroughly monitored to produce adequate results avoiding vinegar notes or metal character. In wet fermentation, also called double-washed fermentation, after cherries are pulped, the parchment is covered by pure water, which enables an extended fermentation time and adds more character to the cup, complex acidity and more refined flavor profile. Other types of fermentation use ice or other tools to prolong the process. Low temperatures tend to increase acidity while higher temperatures tend to increase sweetness. These “positive” fermentations have to be performed in a very controlled way to avoid undesirable microorganism’s growth and off-flavor development. It has been previously mentioned that some of the most important defects that spoil coffee flavor are those derived from undesired microbial fermentation and oxidation. This happens not only in the field but also during storage where negative fermentation and oxidation may occur, producing a number of compounds such as hydrocarbons, aldehydes and ketones in concentrations which decrease the cup value (Toci and Farah, 2008, 2014). Prior to roasting, coffee must be stored in a clean, dry and ventilated mold free and insect free space, located away from odors that

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may interfere with the natural coffee aroma. Traditionally, coffee was stored in jute bags prior to roasting or trading, but as the knowledge of coffee flavor advanced, cuppers were able to identify jute off-notes in the brews from coffees stored for a long period in this type of bag. To avoid this or similar off-notes, inert synthetic materials are currently being used for storage. In some cases, however, the seeds may be deliberately exposed to environments to acquire a specific sensory note. This is the case with the monsooned coffees, which are exposed to the monsoon winds to acquire a musty flavor. Another classical problem derived from inappropriate storage is the growth of coffee berry borer (Hypothenemus hampei), which produces bored seeds considered as defective seeds. The compound 1-(2-methylphenyl)-ethanone has been identified in roasted and ground seeds as a marker of the berry borer infestation (Toci and Farah, 2008, 2014). The presence of a large number of bored seeds has been correlated to increased sourness and bitterness. 9.6 Factors Affecting Coffee Flavor after Roasting 9.6.1 Grinding, Packaging and Storing

Once the coffee is roasted, the whole seeds may be ground (or not) and packaged. They may also be used for instant coffee production. Grinding to produce particle sizes ranging from fine to course will strongly impact the way coffee components are extracted during brewing, and therefore the particle size should vary according to the extraction method used. Of course, it would be preferable if coffee could always be consumed freshly after being roasted, but this is most commonly not possible. Therefore, packaging should be aimed to keep the original character and freshness for as long as possible. Lipid oxidation is one of the chemical reactions that contributes to quality decay during storage. The fatty acids integrity is an important factor for keeping coffee fresh and avoiding the staleness caused by hydrolysis and oxidation of triacylglycerols with formation of free fatty acids (Toci et al., 2013; Rendón et al., 2014), hydrolysis and oxidation of protein, phenolic acids and different classes of volatile compounds have also been reported during storage (Farah et  al., 2006; Rendón et al., 2014; Toci and Farah, 2014).

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Roasting generates a considerable amount of gas, especially carbon dioxide and although one part is released during the roasting process, another part entrapped inside the seeds is slowly released thereafter in a desorption process. Even though roasting plants often use degas machinery, gas continues to release from whole and ground seeds during storage. Acidity/sourness, bitterness and aroma are recognized by tasters as the most important attributes indicating the evolution of the coffee sensory quality upon storage. The formation of sensory perceivable acidic compounds is also one of the prevalent events that occurs during coffee staling. Kreuml et  al. (2013) observed an increase in the brew’s sourness when ground-roasted C. arabica and C. canephora seeds were stored under a vacuum for 18 months, about 60% higher in comparison to the brews prepared from the same freshly roasted seeds. In C. canephora seeds, the perceived sourness doubled at the end of storage compared to the preparation from freshly roasted seeds. Bitterness has also increased. However, the bitter taste intensity in C. canephora beverages was much higher (Farah and Lima, 2018). For these reasons, one-way valves allow the release of carbon dioxide and avoid air from entering into the package. Vacuum or nitrogen atmosphere can also be used to avoid lipid oxidation and prolong shelf life (Farah, 2012; Toci et al., 2013). 9.6.2 Extracting Coffee Flavor: The Brew

The final result of brewing or extraction involves a number of variables such as the type of coffee, particle size, water to coffee ratio, water hardness and quality, temperature and pressure and duration of extraction. Extraction may be followed by filtration (or not) using different filter materials. These factors vary in each of the different methods available for this purpose, and that is why brewing by different methods affects the final brew’s composition and flavor. Like with wine, coffee can offer a variety of sensory notes, but there is no best extraction method for that. Rather, there are preferences or a more suitable method for a given coffee. Among the numerous existing brewing methods, those which perform percolation under pressure such as espresso and Italian moka produce stronger brews, extracting more soluble compounds in general. The electric coffee

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maker is also more efficient in extracting solids than manual percolation (filtered coffee). But for each method, there is a right way to do it so to extract a balanced brew depending on the ground coffee character. Lighter roasted coffees produce brews with a higher acidity. As coffee gets darker, bitterness prevails. In the same way, at the beginning of extraction, the higher solubility of certain compounds make the brew more acidic and at the end of extraction bitter compounds prevail. The size of the hole in the bottom of the manual filter support, for example, can make a huge difference in the final cup because a large hole will increase the speed of extraction and decrease the brew’s bitterness and strength. Therefore, this type of filter support suits very aromatic and aggressive coffees. The amount of soluble solids in the brewed coffee commonly varies from 1.5 to 7 g/100 mL cup (Petracco, 2005; unpublished data from author’s own research). Usually, extraction of water-soluble components including organic acids and esters, caffeine, nicotinic acid, soluble melanoidins and volatile hydrophilic compounds is greater at higher temperatures and pressures. Although the lipid fraction is not water soluble, part of the amount remaining in the seeds after roasting is extracted due to the high water temperature and therefore the lipid fraction is present in the brew as an emulsion. However, oil particles are likely to be retained in filters made of paper or similar types of lipophilic materials. The high pressure used to make an espresso brew and absence of a filter made of paper or similar material to retain the lipids facilitates their extraction directly into the brew. Thus, boiled and to a lesser extent moka, espresso and French press brews contain, in different degrees, higher concentrations of lipids including diterpenes and other components of the lipid fraction (Farah, 2012). The oils present in coffee have the capacity to cover the tongue during ingestion, thus providing the oily and creamy mouthfeel that is characteristic of the beverage (Figueiredo et al., 2015). Triacylglycerols account for approximately 75% (w/w) of total coffee lipids in freshly brewed coffee, whereas free fatty acids account for only approximately 1% (Trugo, 2003). The content of saturated fatty acids, including arachidic, stearic and palmitic acid were reported to be potential discriminators of the quality of specialty coffees, indicating better sensory quality. Stearic and arachidic acid were found to contribute to coffee body and increase in flavor, being correlated with fragrance and

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aromatic compounds beneficial to quality. Conversely, the content of unsaturated fatty acids (elaidic, oleic, linoleic and linolenic acids) were reported to be negatively correlated with sensory quality, especially elaidic acid, a trans-isomer of oleic acid. This may be attributed to the propensity of unsaturated fatty acids to oxidize leading to the development of rancidity and in many cases to the formation of undesirable aromas in oils. The content of unsaturated fatty acids have also been associated with less intense acidity, fragrance, flavor and body, which are highly valued in specialty coffees (Figueiredo et al., 2015). In addition to the classic methods employing hot water, there are a number of new cold brewing methods in which extraction lasts for a varied period of time (about 6–48 hours) at room temperature (21– 25°C) or in cold water under refrigeration. The latter is usually applied for fruity fermented types of coffees. Often concentrated cold brews are made for later dilution in cold or hot water. The cold water makes extraction more difficult for compounds that are not water soluble and decreases the rate of mass transfer and extraction of water-soluble compounds, producing a lower concentration of soluble solids when the same extraction time is compared. However, eventually, after 7 hr at room temperature, extraction may equal or exceed that of 95°C water. Extraction of chlorogenic acids and caffeine follows first-order kinetics and extraction rate decreases after the first 3 hr. From about 7 to 24 hr, extraction does not seem to increase significantly at room temperature. Finally, as opposed to what occurs in the fast hot water methods, the size of particles does not seem to be as important for extraction of these water-soluble components in cold brew since there is enough time for the water to penetrate the coffee particles and extract the compounds (Fuller and Rao, 2017). Studies on different types of cold brewing as well as the investigation of bitter compounds are still needed. Galactomannans and type II arabinogalactans are the predominant polysaccharides that pass into the brew, being the first more soluble. These polysaccharides are important for the body of the brew since they represent approximately 15–25% of its dry weight (Petracco, 2001; Bekedam et al., 2008). According to Petracco (2001), a typical amount of soluble fiber in espresso coffee is 800 mg/100 mL, and a regular percolation method produces approximately 200 mg/100 mL. Similarly, Díaz-Rubio and Saura-Calixto (2007) reported 470–750

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mg soluble fiber in 100 mL brewed coffees. These polysaccharides increase the brew’s viscosity (body) and help to trap aroma compounds to remain in the brew. Coffee’s acidity is due to aliphatic acids such as acetic, formic, malic, citric and lactic acids, as well as chlorogenic and quinic acids. Acids are quite soluble and they are some of the first compounds to be extracted. Based on comparison with values from methanolic extracts, approximately 80–100% of chlorogenic acids are extracted in home coffee brewing. Bitter phenolic derivatives formed at the end of the roast, however, are not as readily extracted since they are more lipophilic (Clifford, 2000; Farah, 2012). The brews of C. arabica seeds have higher perceived (desirable) acidity compared to C. canephora, and this may be one of the reasons for its superiority in the market, although C. canephora is often blended with C. arabica to increase the brew’s “body.” Medium or light-medium ground-roasted C. arabica brews tend to have a pH slightly lower (4.3– 5.2) than C. canephora brews (5.3–5.8) and darker roasted C. arabica brews tend to present a slightly higher pH (5.0–6.3) which may highlight the bitter taste (Farah, 2012; Farah and Lima, 2018). Acids are not only responsible for perceived acidity but also contribute flavor in different ways and intensities. For example, citric acid has a fresh and short-lived tartness and with flavors like lemon and orange. When associated with phosphoric acid, it may have notes of grapefruit. Phosphoric acid alone tends to impart sweet notes and quinic acid a “clean” finish, malic acid is present in many fruits and imparts fruity, apple and sometimes pear, peach or plum notes to the beverage. It has a smooth lingering taste and tartness not as sharp as that of citric acid but longer lasting. Malic acid is used in the food industry to enhance flavor, mostly in combination with citric acid. Lactic acid usually conveys a buttery note. Depending on both the nature and predominance, acidity may be desirable or undesirable. The desirable acidity contributes to the vivacity and freshness of coffee brews, increasing the sweetness perception and in some cases providing a dry fruit taste. An over-expressed acidity, on the other hand, may be unpleasant and relate to unusual tastes in coffee drinks. Acidity resulting from citric and malic acids, for example, is usually desirable and can indicate good quality. On the other hand, acetic acid resembles fermentation. When in small

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amounts acetic acid contributes to global flavor and can impart a pleasant sharpness to the beverage but may be greatly unpleasant in high concentrations. In fact, not only acetic but also oxalic, propionic and butyric acids tend to affect quality negatively (Borém et al., 2016; Farah and Lima, 2018). Similarly, tartaric acid may produce a sour taste at high concentrations, but at low concentrations it can present grape-like or winey notes. These acids often originate from excessive or inappropriate fruit fermentation during postharvest processing and can also be produced as the fruits overripen and ferment on the tree, as is the case with defective black seeds. Some of these undesired acids can also be produced during roasting. In addition to objectionable acids, black and sour defective seeds seem to have more acidic characteristics than regular seeds. Also, immature defective seeds were reported to have a lower acidity, since acidity increases with maturation (Farah and Lima, 2018). Caffeine, trigonelline, nicotinic acid, amines and other minor nitrogenated compounds (Table 9.4) are also readily soluble in hot water. Their contents vary together with those of soluble solids. Approximately up to 0.3 and 0.7 g of potassium have been reported in 100 mL brews at 8 and 20% (coffee/water), respectively (Petracco, 2007; Antonio, 2011). The content of phosphorus was reasonable (50 mg/100 mL brew) and low amounts of sodium (approximately 3 mg/100 mL brew) were found in a brew prepared at 20% (w/v) (Antonio et al., 2011). Perceived acidity tends to decrease as well after brewing. Chemical reactions continue to occur in the cup and hydrolysis of week organic acids is one of them, contributing to dramatic changes until the beverage is consumed. Keeping brewed coffee at a high temperature reduces chlorogenic acids and lactones concentrations, producing sensory changes, but a relationship that describes such changes to staleness does not seem to be scientifically established (Farah and Lima, 2018). The profile of other non-volatile compounds, as well as volatile compounds and flavor, are also modified by heating the coffee brew. Kumazawa and Masuda (2003) observed that heating the coffee brew increased or produced attributes of pungency, putrid, heavy (tallowry), sour and caramel-like odors. They associated the increased concentration of methanethiol to the putrid and pungent odors, acetic acid and

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Table 9.4  Non-Volatile Composition of Roasted Coffee Brews

COMPOUNDS Water Simple sugarsb Soluble polysaccharidesc Proteins Caffeine Trigonelline n-Methylpyridinium Thiamin Riboflavin Nicotinic acid Pyridoxine Folate β-Carbolins (norharman and harman) Serotonin Melatonin Polyamines (spermine and spermidine) Total lipids Diterpenes (cafestol and kahweol) Tocopherols (α, β, γ) Phylloquinone Chlorogenic acids Sum of other phenolic compounds Aliphatic acids and quinic acid Ascorbic acid Minerals: total ashes Potassium Calcium Sodium Phosphorus Iron Zinc Manganese Melanoidins

CONTENT RANGEa (MG/100 ML WET BASIS) (FROM C. arabica OR BLENDS OF C. arabica AND C. canephora sp.) 94,000–98,500 (total solids 1.5–6%) 0–100 (one report up to 200 mg) 200–700 (commonly between 400–500) 120–400 50–380 (commonly between 50–150) 12–50 2.9–8.7 0.001 0.177 0.8–10 (commonly up to 5) 0.002 1 0.004–0.08 0–1.4 0.006–0.008 0.4 180–400 (depends on the preparation method) 0.2–1.5 (paper filtered); 2.6–10 (boiled) 0.01–tr (unfiltered coffee) 0.1 32–500 (commonly 50–150) 0.1–0.2 692–2140 0.2 150–500 115–700 2–4 1–14 3–50 0.02–0.13 0.01–0.05 0.02–0.05 500–1500

Source: Adapted from Farah, 2017. a Chemical composition reported for brews from medium roasted ground beans (C. arabica and C. canephora species). Content varies with blend, roasting method and degree, grid, brewing method, amount of coffee powder to water and analytical methods. b Arabinose, mannose, galactose, sucrose and minor saccharides. c Mainly arabinogalactans and type II galactomannans; pH varies from 4.3 (acidic coffee, light roast), to 5.8. Common values around 5.0.

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3-methylbutanoic acid with the sour odor, 2-furfuryl methyl disulfide and 4-hydroxy-2,5-dimethyl-3(2H)-furanone with the heavy (tallowry) and caramel-like odors. They also observed a decrease in the concentration of compounds associated with a roasty odor (including 2-furfurilthyol and 3-marcapto-3-methylbutyl formate) and assumed that they were changed by oxidation, thermal degradation and/or hydrolysis. Table 9.4 summarizes the concentrations of reported nonvolatile components in roasted coffee brews. 9.7 Concluding Remarks

Complex reactions take place during roasting at high temperatures and considerably modify coffee’s chemical composition and flavor. Currently, expert roasters can control these reactions by adjusting the roast profile to the original coffee’s character, which enables them to improve the beverage quality. However, a number of additional aspects determine the brew’s composition and must be taken care of in order to reveal the sensory experiences inherent to coffee.

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Frank, O., S. Blumberg, C. Kunert, G. Zehentbauer, and T. Hofmann. 2007. Structure determination and sensory analysis of bitter-tasting 4-vinylcatechol oligomers and their identification in roasted coffee by means of LC-MS/MS. Journal of Agricultural and Food Chemistry 55:1945–1954. Fuller, M., and N.Z. Rao. 2017. The effect of time, roasting temperature, and grind size on Caffeine and chlorogenic acid concentrations in cold brew Cofee. Scientific Reports 7:17979. Ginz, M., H.H. Balzer, A.G.W. Bradbury, and H.G. Maier. 2000. Formation of aliphatic acids by carbohydrate degradation during roasting of coffee. European Food Research and Technology 211:404–410. Jaiswal, R., M.A. Patras, P. Eravuchira, and J. Kuhnert. 2010. Profile and characterization of the chlorogenic acids in green Robusta coffee seeds by LC-MSn: Identification of seven new classes of compounds. Journal of Agricultural and Food Chemistry 58:8722–8737. Kölling-Speer, L., and K. Speer 2005. The Raw Seed composition. In: Espresso Coffee, the Science of Quality, eds. A. Illy, and R. Viani, 148–178. Elsevier Academic Press: Milan, Italy. Kreuml, M.T.L., D. Majchrzak, B. Ploederl, and J. Koenig. 2013. Changes in sensory quality characteristics of coffee during storage. Food Science and Nutrition 1:267–272. Kumazawa, K., and H. Masuda. 2003. Investigation of the change in the flavor of a coffee drink during heat processing. Journal of Agricultural and Food Chemistry 51:2674–2678. Lercker, G., M.F. Caboni, G. Bertacco, E. Turchetto, A. Lucci, R. Bortolomeazzi, N. Frega, and F. Bocci. 1996. Coffee lipid fraction I. Influence of roasting and decaffeination. Industrie Alimentari 35:1057–1065. Luisa, P.F., M.B. Flávio, C.R. Fabiana, S.G. Gerson, HdS.T. Jose, and R.M. Marcelo. 2015. Fatty acid profiles and parameters of quality of specialty coffees produced in different Brazilian regions. African Journal of Agricultural Research 10 (35):3484–3493. Maetzu, L., C. Sanz, S. Andueza, M.P. De Peña, J. Bello, and C. Cid. 2001. Characterization of espresso coffee aroma by static headspace GC-MS and sensory flavor profile. Journal of Agricultural and Food Chemistry 49:5449–5444. Mazzafera, P., T.W. Baumann, M.M. Shimizu, and M.B. Silvarolla. 2009. Decaf and the steeplechase towards decaffito the coffee from caffeinefree Arabica plants. Tropical Plant Biology 2:63–76. Mazzafera, P., F. Schimpl, and E. Kiyota 2018. Proteins of coffee beans: Recent advances. In: Coffee: Production, Quality and Chemistry, ed. A. Farah, 431–444. Royal Society of Chemistry: London, UK. de Melo Pereira, G.V., D.P. de Carvalho Neto, A.I.M. Júnior, Z.S. Vasquez, A.B. Medeiros, L.P. Vandenberghe, and C.R. Soccol. 2018. Exploring the impacts of postharvest processing on the aroma formation of coffee beans – A review. Food Chemistry 272:441–452. Monteiro, M.C., and A. Farah. 2012. Chlorogenic acids in Brazilian Coffea arabica cultivars from various consecutive crops. Food Chemistry 134:611–614.

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10 Q ualit y of the Final P roduct and C l as sifi cati o n of G reen C offee M A R IO RO B E R T O F E R N A N DE Z A L D U E N DA Contents

10.1 Introduction 311 10.2 Commodity Coffee Grading Systems 314 10.3 The Specialty Coffee Grading System 319 10.4 Descriptive Cupping 321 10.5 Applied Case of Descriptive Cupping: Assessing the Effect of Processing Methods in Yunnan 324 10.5.1  Introduction and Objectives 324 10.5.2 Methods 324 10.5.2.1  Farm Selection and Processor Training 324 10.5.2.2  Processing Treatments 325 10.5.2.3  Cupping of Samples 326 10.5.2.4  Data Analyses 327 10.5.3  Results and Discussion 328 10.5.3.1  Analyses of Attribute Scores 328 10.5.3.2  Analyses of Descriptors 329 10.5.3.3  Multiple Factor Analysis 335 10.6 Concluding Remarks 338 References 339 10.1 Introduction

This chapter discusses the concepts of the quality and classification of green coffee, two concepts that when combined result in the concept of “grading.” Grading can thus be understood as the formal classification 311

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of a product based on quality. The concepts of quality and grading for most agricultural products tend to be simple. For example, the U.S. Department of Agriculture (USDA) standard for corn classifies grades 1 through 4 based on bulk density, percentage of heat-damaged kernels, percentage of total damaged kernels and percentage of broken corn and foreign material (USDA, 1996). However, for complex products like coffee, grading becomes a challenging task. There are several reasons for this, namely, the botanical diversity of coffee, its long value chain, its diverse markets and its chemical complexity. First, the botanical diversity of coffee: The term “coffee” does not refer to one botanical species but may mean any of several species of the genus Coffea (C. arabica, C. canephora, C. liberica and others). Each of the species has radically different morphological, chemical and sensory characteristics as well as a different market, and thus quality cannot be understood in the same terms for all coffee species. Second, coffee’s long value chain: Coffee is traded in many forms along the value chain. It can be traded as freshly harvested coffee cherries (as in Mexico); in the form of dry parchment (as in Colombia) or dry cherries (as in Mexico as well); as unsorted hulled coffee (as in Brazil); as sorted green coffee (as it is traded internationally), as roasted coffee, as an industrialized product like an instant coffee or a coffee pod or even as a ready-to-drink beverage. Each of these forms have their own quality specifications and classification. Third, coffee’s diverse markets: Coffee is not all the same and coffee does not all have the same value. From the low-quality Robusta coffee that is the raw material for mainstream instant coffee at $1.92 per kg (ICE, 2015a) to the most expensive, award-winning, Panamanian natural geisha varietal at $771.47 per kg (Stoneworks and Specialty Coffee Association of Panama, 2013), the value of the green coffee bean can vary by a factor of over 400. The reason for such disparity is the existence of a flourishing specialty coffee industry within the broader, generic coffee industry. The specialty coffee industry is growing fast, with consumers willing to pay a premium for high-quality coffees. According to the National Coffee Association of the United States (NCA, 2014), the daily consumption of specialty coffee beverages increased from 9% of U.S. adults in 2000 to 34% in 2014, and the  value of the specialty coffee share represented 51% of the total coffee market value in the United States in 2014. This means the yearly

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retail value of specialty coffee is about $16 billion in the United States alone (SCAA, 2012a). By definition, the specialty coffee industry values “quality” (SCAE, 2014), yet the meaning of that “quality” will be discussed later. Fourth, coffee’s chemical complexity: The flavor remains the most important parameter for coffee consumers (Mori et al., 2008). However, coffee flavor is one of the most complex flavors known, which is why research efforts have been made to understand it for over a century (Sunarharum et al., 2014). More than 1000 volatiles have been identified in roasted coffee, of which at least 70 are considered potent odorants (Michishita et  al., 2010). Besides these volatile compounds affecting aroma and the olfactory component of flavor, other non-volatile compounds also influence the taste component of coffee flavor (Flament and Bessière-Thomas, 2002; Sunarharum et  al., 2014). The most relevant characteristic of coffee, namely, its flavor is the result of the complex interaction of thousands of compounds, and all the steps along the production chain, from the terroir to the preparation of the brew, have an impact on the final flavor outcome (Sunarharum et al., 2014). Within this whole complexity, the scope of this chapter needs to be better defined for the reader. Among the different Coffea species, unless specified otherwise, this chapter is referring to C. arabica. The reason for this is that quality assessment is much more evolved in the case of Arabica versus the other species. From the entire value chain, this chapter will focus on the quality of green coffee alone (the dried, hulled and unroasted coffee bean). The reason is that green bean is the state in which coffee is traded internationally, between producing and consuming countries, and thus this is the state where most controversy over quality occurs. Having chosen the scope of green Arabica coffee, vast market diversity and a vast flavor complexity remain, and these need to be understood to grade coffee accurately. The mere definition of “quality” is different depending on which market we are referring to. For the commodity market, the one that places coffee on supermarket shelves and the main foodservice chains, quality most often means “free from defects” or “conformance to requirements.” For the specialty coffee industry, on the other hand, best represented by the socalled “Third Wave Cafés,” quality means “a degree of excellence,” as can be understood from the definitions of “specialty coffee” by the

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trade associations. For the Specialty Coffee Association of Europe, specialty coffee was defined as a “crafted quality coffee-based beverage, which is judged by the consumer […] to have a unique quality, a distinct taste and personality different from, and superior to, the common coffee beverages offered. The beverage is based on beans that have been grown in an accurately defined area, and which meet the highest standards for green coffee and for its roasting, storage and brewing” (SCAE, 2014). Similarly, for the Specialty Coffee Association of America (SCAA), specialty coffee is defined as “the highest-quality green coffee beans roasted to their greatest flavor potential by true craftspeople and then properly brewed to well-established SCAA developed standards” (SCAA, 2012b). These two radically different understandings of “quality,” “conformance to requirements” versus “degree of excellence,” give way to the two main “schools” of coffee grading coexisting today. The traditional grading systems for the commodity market, which were mostly developed by each producing country during early to mid-twentieth century, and the specialty coffee grading system which was developed by the SCAA in the late twentieth century and increasingly applied all over the world to date. The main sense of advancement in the assessment of coffee quality for the last 20 years has been the evolution of coffee cupping, from “an informal art, passed on through generations by word of mouth […] and thought of as a very specialized skill, taking years to acquire and belonging to a very few select individuals” (Lingle and Menon, 2017) to a skill set that is taught throughout the world by coffee trade associations, by the Coffee Quality Institute and by cupping schools in both consuming and producing countries. This is not just about the “popularization” of coffee cupping. The cupping protocols have undergone a qualitative evolution, as training tools, sensory references, “flavor wheels” and cupping interfaces keep evolving. The potential of cupping as a rapid sensory descriptive tool specific to coffee has also led to some interesting applications of cupping as a research tool. 10.2 Commodity Coffee Grading Systems

Green coffee grading dates to the beginning of the international coffee trade. A green coffee price list from an Amsterdam coffee trader, dated

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on 24 September 1794 (Haggam, 2012) shows the price of coffee from different origins (Yemen, Java, Ceylon, Reunion, Martinique, Suriname and Santo Domingo) but also from different grades from each origin. For example, Suriname “Blue” is listed at 6.25 florins per ball, Suriname “Good for Shops” grade at 6.13 florins per ball and Suriname “Unclean” grade at 5.25 florins per ball. With the advent of the futures exchange system, such as the “Coffee Exchange in the City of New York,” coffee grading became systematized and during the twentieth century, most coffee producing developed their own grading standards (Rochac, 1964). There are three categories of green coffee grading standards, namely, (a) international standards (issued by the International Organization for Standardization – ISO), (b) national standards (issued by official standardization bodies in both producing and consuming countries) and (c) trade standards (issued by a futures commodity exchange). Although they are private standards, trade standards are the most widely used by the coffee industry. In the case of Arabica coffee, the trade standard is owned by Intercontinental Exchange (ICE) and is called “Coffee ‘C’ Rules.” The main specification of the “C” Rules is the “number of imperfections,” which is a weighed count of foreign matter and defective beans in a 350 g sample (ICE, 2015b). The existence of different grading standards per country throughout the twentieth century, from a global point of view, became a complicated, obscure system, only mastered by a handful of traders. As a couple of examples: (a) the designation Brasil Santos 2/3 mtgbss fc gtfr, means an Arabica coffee exported out of the Brazilian port of Santos, with a maximum of eight defects, medium to good bean (screen 15/16), strictly soft, fine cup, good to fine roast. All those terms (defect count, good bean, softness, fine cup, fine roast) are defined in the Brazilian standard. Note the difference with the following example: (b) the designation Guatemala SHB EP Huehuetenango, which means Arabica coffee from the Huehuetenango region in Guatemala, is a strictly hard bean, with European preparation. Note that in the case of Brazil, “soft” is a desirable characteristic, in contrast with Guatemala “strictly hard bean” is a desirable characteristic. This is because in Brazil “soft” refers to a soft taste in the cup (as opposed to astringent or faulty), while in Guatemala “strictly hard” refers to bean density, which in turn is linked to the altitude of cultivation according to the Guatemalan standard (Supremo, 2017).

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Even though the different grading systems vary by country, an excellent systematization (and critique) of the different systems was done by Feria-Morales (2002), who explains that the majority of them use at least some of the following elements: a. Definition: The current international standard (ISO 3509:2005) defines the most commonly used terms relating to coffee and its products. This standard has been mirrored by several countries’ national standards systems. It defines the terms for the parts of the coffee fruit and terms related to green coffee, roasted coffee and roasted processes (DGN, 2008a). b. Designation: The designation of the product usually includes the geographical origin of the beans (a country like Colombia, a region like Huehuetenango in Guatemala, or a port of export like Santos in Brazil), the botanical species of the lot (usually Arabica or Robusta, in countries that produce both), specifications about the process, the crop year and the grade or classification itself. As an example, “Mexico Prime Washed 2017/18.” In several cases, the altitude of cultivation or the region of origin influences the quality grading. For example, in Mexico, the quality grades are officially tied to the altitude of cultivation (DGN, 2008b). c. Composition: This refers to the chemical composition of the beans. Unlike many other food products, chemical composition is usually not included in green coffee standards, except for moisture content. Moisture content is usually specified at less than 12% or less than 13%. The current international standard for the measurement of moisture is ISO 6673:2003 and it stipulates the method of mass-loss determination using an oven at 105°C for 16 h (ISO, 2003). However, the most widely used method for moisture content determination in the industry is the use of commercial grain moisture meters (i.e., by capacitance of the sample) which are not always calibrated against the official method. d. Defects: In almost all green coffee grading standards, there are specifications for “defects,” including foreign matter and defective beans. The current international standard (ISO, 2005) stipulates a determination of foreign matter and defects

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by mass percentage. Although this standard has been mirrored by several countries, this procedure is rarely used by the industry. Most countries have systems based on categorizing the defective beans by defect type and then applying different weights to each defect category depending on their severity in order to obtain a final defect count. For example, in the Brazilian system (MAPA, 2003), defects are counted on a sample of 300 g and defects are classed as intrinsic or foreign, and within each class, different defect categories have different weight (i.e., one black bean equals one defect, but from two to five insect-damaged beans equals one defect). Systems in other countries would be different; for example, in Colombia the sample size is 500 g (ICO, 2013). e. Bean size and shape: Bean size is usually expressed as a percentage of beans retained above or passing through specific screens and the screen aperture is customarily expressed in 1/64th of an inch. Thus, for example, the ICE (2015b) standard specifies “The coffee is of such bean size that (i) fifty percent (50%) of the coffee sampled screens fifteen (15) or larger, and (ii) no more than five percent (5%) of the coffee sampled screens below fourteen (14).” In this case, “screen 15” means 6.00 mm and “screen 14” means 5.60 mm. In a comparison made by ICO (2013) of the green coffee grading standards from nine producing countries and four consuming countries, the bean size was found to be the main parameter for coffee grading. The bean size can be specified by using designations (i.e., “medium”), letters (i.e., Tanzania AB) or numbers. f. Color: In some countries (i.e., Brazil, Kenya), the color of the green bean is part of the specifications. The international standard (ISO, 2005) stipulates the categorization of coffee color in the following colors: blueish, greenish, grayish-green, olive-green, whiteish, yellowish and brownish. g. Roasting characteristics: Some national standards include roasting characteristics such as appearance, color of the center cut and number of quakers (pale beans), as specifications for different grades. h. Cup profile: Admittedly, the most important quality characteristic of coffee should be the cup profile, as it is the only

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attribute of the green coffee bean that will be noticeable to consumers after roasting and brewing. However, in the case of green bean standards, the cup profile is minimized usually to “the absence of defects,” while other specifications such as the bean size become the main criteria for grading. The reason for this can be hypothesized as an attempt from standardization bodies to use “objective” measurements instead of relying on the verdicts of “expert tasters.” Fortunately, both sensory science and the cupping practice have greatly evolved since the creation of most current commodity standards, and next sections will explore the role of flavor in modern coffee quality work. Even the countries that do incorporate cup quality into their national standards, like Brazil, would benefit from modernization of their current official cupping practices. A notable exception in this area is Ethiopia. Since the creation of the Ethiopian Commodity Exchange (ECX), Ethiopia has adopted cup quality as the main specification for grading. In the new Ethiopian system, cup quality is worth 60% of the weight when determining the preliminary grade and coffees that get grades 1 through 3 in the preliminary assessment undergo a specialty cupping to assess their potential as specialty coffee (ECX, 2015). All the cuppers grading coffees officially at the ECX must be licensed as a Q Grader®, to ensure their competency to grade specialty coffee. Different countries assign a different degree of importance to each of the eight variables (items a–h) listed above, which makes it confusing when navigating the different national grading systems. Feria-Morales (2002) categorized the different green Arabica grading systems into three groups, namely, (a) Central America, where classification is based on altitude, region, market (i.e., “European” or “American” preparations), acidity/body/cleanliness of brew and absence of off-flavors; (b) Africa, Asia and South America, where classification is based on appearance and acidity/body/cleanliness of brew; and (c) Brazil, where the criteria are defect count, bean size, bean color and softness versus hardness or presence of Rio-type defects in the brew.

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10.3 The Specialty Coffee Grading System

As the importance of the specialty coffee industry increased exponentially, the limitations of the national or commodity grading systems for the new industry became clearer. Part of it was an almost philosophical contraposition where the commodity grading standards take the concept of quality as compliance with specifications, while the new specialty coffee industry takes it more often as a degree of excellence. But from a more practical point of view, the specialty coffee industry seeks differentiation, while the commodity standards sought uniformity within a grade. For example, Colombia exports millions of “Excelso Grade” bags, though they do not all taste the same. In fact, every lot of coffee (and ultimately every bean) has its own flavor character as anybody who has started cupping coffee soon understands. In the viewpoint of consumers that pay for specialty coffee, the only quality specification that counts is the coffee flavor. All other green bean specifications are only helpful in as much as they correlate to the flavor. Thus, with their reduced focus on flavor and their complicated diversity, the national green coffee grading standards become too limiting for the needs of the specialty coffee industry. As a response to these needs, the SCAA developed the current specialty cupping protocol between 1999 and 2004 (Lingle and Menon, 2017), basing it on the cupping method by Lingle (1986). The SCAA cupping protocols (SCAA, 2009a), together with the SCAA green coffee grading protocols (SCAA, 2004, 2009b), became the new tools for assessing green bean quality for the specialty industry. The term “specialty coffee” has been widely used with very different meanings, and the SCAA decided to define the meaning of the term at the green bean level through the issue of the Specialty Grade Coffee Standard. The specialty grade standard as such is not certified by any certification body. However, the Coffee Quality Institute (CQI), established in 1995, certifies green coffee complying to the “Q Coffee Standard,” which is largely based on SCAA’s Specialty Grade Coffee Standard and uses SCAA’s protocols (SCAA, 2004, 2009a & 2009b) as assessment tools (Fernandez Alduenda, 2017; Lingle and Menon, 2017; Thomas et al., 2017). Although the Q Coffee standard originally mirrored the SCAA Specialty Grade Coffee standard, both standards have slightly

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diverged over the years. The SCAA reduced the allowance of quakers per 100 g of roasted from 3 to 0, while an allowance of 3 quakers per 100 g was kept by CQI for the Q Standard. In 2016, SCAA added a water activity specification to the standard (SCAA, 2016) but this specification has not been adopted by CQI. Table 10.1 presents a summary and comparison of both SCAA’s Specialty Grade standard and CQI’s Q Coffee Standard. In essence, both standards are the same and, except for the quaker specification, a coffee that complies with one of them will be complying with the other one. This is a pass/fail standard, meaning that a sample of coffee must comply with all the specifications to receive the grade and there are no other grades aside of Specialty Grade/Q Coffee. Noncomplying coffee has been called “commercial coffee” or “below specialty grade” coffee. Certification of Q Coffees is done through CQI’s “In-Country Partners” (ICP). At the time of this writing, CQI had 23 ICP’s in 21 countries (CQI, 2017a). When they receive green coffee samples for grading, ICP’s are required to summon three licensed “Q Graders” to grade the sample. Q Graders are cuppers who have passed a rigorous certification encompassing cupping skills, green coffee grading skills and various sensory skills (Lingle and Menon, 2017). In the case of a standard for which cupping is the main measurement tool, the certification of the cuppers’ competencies became indispensable and for over 10 years, CQI has been training cuppers and certifying the ones who Table 10.1  Comparison of SCAA’s Specialty Grade Standard and CQI’s Q Coffee Standard SCAA: SPECIALTY GRADE STANDARD

CQI: Q COFFEE STANDARD

Scent of green coffee Roasted grading

No primary defects Up to five secondary defects 10.00–12.00% moisture Water activity below 0.70 Free of foreign odor No quakers

No primary defects Up to five secondary defects 10.00–12.00% moisture No standard for water activity Free of foreign odor Up to three quakers

Cupping score

Minimum of 80.00

Minimum of 80.00

GRADED ASPECT Green coffee defects

Moisture and water activity of green coffee

TEST METHOD Defect count in 350 g (SCAA, 2004, 2009b) Not specified

Not specified Quaker count in 100 g roasted coffee (SCAA, 2004) SCAA, 2009a

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pass the 20 tests of the Q Grader examination. To this date, CQI has listed 5308 cuppers as licensed Q Graders (CQI, 2017b). An important concept in the case of the specialty grading system is “calibration.” The concept of calibration is analogous to the calibration of a measuring instrument against a standard. In this case, the “measuring instrument” is the cupper, while the standard is thought to be the “specialty coffee market” or, from another point of view, the cupping criteria of cuppers involved in the specialty coffee trade. All cuppers are required to demonstrate “calibration” when they first get certified as licensed Q Graders and go through a one-day “calibration” every 36 months to maintain their certification. The calibration tests required for maintaining the Q Grader License imply cupping three sessions of six samples each and two out of the three sessions need to be passed for the cupper’s certification to be renewed. In each session, the cuppers’ test grades depend on how close their cupping scores for each attribute and for each sample’s final score are to the group’s mean. A cupper can also fail a cupping session for wrong use of the cupping form or incorrect defect detection. 10.4 Descriptive Cupping

The SCAA Cupping Protocol has been largely described and discussed elsewhere (SCAA, 2009a; Fernandez Alduenda, 2017; Lingle and Menon, 2017; Thomas et  al., 2017). However, in recent years, there have been some advancements related to specialty coffee cupping that point at new applications for cupping as a tool beyond quality control activities. As the “Third Wave” of the specialty coffee industry grows, the need for more accurate descriptions of coffee flavor increases. That is the reason several advancements around coffee cupping point to some degree of convergence between cupping and descriptive sensory analysis. One of those advances is the development of sensory references that demonstrate aroma or flavor notes for cupper training. Two recent examples of this are (a) the “Coffee Flavor Map T100,” developed by the Korea Coffee Promotion Foundation (KICCI) and SCENTONE (SCENTONE, 2016), which is a relatively low-cost set of 100 olfactory references for aroma notes found in coffee developed using both cuppers and gas chromatography–mass spectrometry/

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olfactometry (GC-MS/O); and (b) FlavorActiV™ flavor standards for coffee which is a set of 24 flavors found in coffee that are distributed as soluble solids which are dissolved in water for cupper training (FlavorActiV, 2017). Another advancement is the development of a “Sensory Lexicon” (WCR, 2017), a descriptive, quantifiable and replicable lexicon designed to “enable coffee scientists to conduct research that will make coffee better – starting with the seed itself ” (WCR, 2017). In its second edition, the lexicon has incorporated FlavorActiV references officially. Spencer et  al. (2016) took the WCR lexicon terms, categorized them and structured them to produce a descriptive “Flavor Wheel” for coffee flavor notes. Cupping interfaces have also become a useful advancement, as they allow cuppers to enter the cupping results cooperatively into a database. An interesting example is Tastify, which also collects descriptive data, such as the fragrance/aroma notes, flavor notes, aftertaste notes, quality of acidity, body and balance, and so on. A flavor profile is produced by Tastify, based on the frequency of use of each descriptor by cuppers. A methodology named “descriptive cupping” was developed in 2012–2014 at the University of Otago, New Zealand (Fernandez Alduenda et  al., 2014; Fernandez Alduenda, 2015) to interpret descriptive data entered through a cupping interface, using statistical tools borrowed from other sensory applications (Lawrence et al., 2013). The aim of this methodology was to assess the use of a cupping panel to obtain descriptive coffee flavor profiles. Specifically, descriptive cupping focuses on characterizing the sensory profile of coffee using descriptive data generated using the SCAA (2009a) cupping protocol. In this protocol, quality scores are used to grade coffee while the descriptive data is usually disregarded. However, the descriptive data collected by the SCAA cupping protocol may provide a means to obtain a coffee flavor profile in origin countries that lack advanced sensory facilities and descriptive panels. Descriptors from the cuppers are grouped into categories. A contingency table is constructed with samples as columns and categories as rows. The descriptive space is visualized using non-symmetric correspondence analysis (NSCA) (Fernandez Alduenda et al., 2014). Descriptive cupping data can be integrated with other types of data such as cupping

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scores or even qualitative data using multiple factor analysis (MFA) (Fernandez Alduenda, 2015). The performance of descriptive cupping has been validated against more traditional descriptive analysis techniques. Wilson et al. (2015) trained a descriptive panel and developed a vocabulary of 24 descriptors for coffee aroma (7 descriptors), taste (4 descriptors), flavor (7 descriptors) and aftertaste (6 descriptors). Coffee samples profiled through descriptive cupping were also analyzed by the descriptive panel, and 13 descriptors were found to significantly (p  45.93, at a confidence level of 95%) and which are not (60 descriptors with χ2