COFFEE

Volume 2: Technology

COFFEE

Volume 1: Chemistry Volume 2: Technology Volume 3: Physiology Volume 4: Agronomy Volume 5: Related Beverages Volume 6: Commercial and Technico-Legal Aspects

COFFEE Volume 2: TECHNOLOGY

Edited by

R. J. CLARKE Formerly of General Foods Ltd, Banbury, UK

and

R. MACRAE Department of Food Science, University of Reading, UK

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WITH 42 TABLES AND 81 ILLUSTRATIONS

© 1987 ELSEVIER SCIENCE PUBLISHERS LTD First Edition 1987

Reprinted 1989 Softcover reprint of the hardcover 15t edition 1987

British Library Cataloguing in Publication Data

Coffee. Vol. 2: Technology 1. Coffee I. Clarke, R. J. II. Macrae, R. 641.3'373 TX415

ISBN-13: 978-94-010-8028-6 e-ISBN-13: 978-94-009-3417-7 001: 10.1007/978-94-009-3417-7

Library of Congress CIP data applied for

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Preface

The present volume, Volume 2 in this planned series on coffee, deals with processing and follows on naturally from the first volume on the chemistry of coffee, which described its numerous constituents in the green (raw) and various product forms.

We have already remarked that coffee has great compositional complex­ity, and this complexity of understanding extends when we come to consider its processing; that is, the many processes involved in the roasting of green coffee and its subsequent conversion into a consumable brew, especially through extraction and drying into an instant coffee. The simple brewing of roasted and ground coffee with water in the home also possesses considerable mystique and needs know-how for optimal results. The choice of green coffees from an almost bewildering array of different types available, through species/variety differences and different methods of processing from the coffee cherry to the green coffee bean, needs understanding and guidance. Furthermore, various forms of pre-treatment of green coffee before roasting are available. Some of these are little known, but others such as decaffeination, for those who desire roasted or instant coffee with little or no caffeine, are now becoming well established. Finally, both the processing of coffee cherries to coffee beans, leaving a range of different waste products (pulp, hulls, husk, parchment, etc.), and of roasted coffee after industrial aqueous extraction, leaving spent coffee grounds, provide waste products that have found considerable commercial value in different ways.

v

VI PREFACE

In our nine chapters, therefore, all these subjects are dealt with in detail, bringing together much information that has not generally been available previously in the English language. Particularly, in the basic unit operations of roasting-grinding-extraction-drying, the approach has been that of considering the fundamentals of the subject, through the well established discipline of chemical (food) engineering. This approach to coffee processing has been applied by a number of workers in the last two decades as described in the Appendix (section 5); though, as will be seen, much remains to be revealed and understood in this complex field. Much information and opinion is empirical, so that, particularly in instant coffee manufacture, there are many elements of craft, skill and know­how in plant operation. However, it is not the aim of this volume to cover these facets, and indeed much of this is necessarily known only to the manufacturers themselves; though an indication of preferred or 'wished-for' modes of operation can be seen on studying the numerous patents (probably some separate 1000) on coffee that have been granted. Only a selection of these patents can be given in this volume, with a preference towards noting the patents granted in the USA, though many of these may well also be issued in other countries. There is no doubt that the intense competition among the major instant coffee manufacturers of the world has been the spur to great progress in the quality of coffee products over the last three or four decades.

A vexing problem common now to all technical texts on the engineering of food and other manufacturing processes is in the choice of units for the various physical properties of substances and process parameters involved. Much existing information is expressed in so-called engineering units (foot-pound-hour system), especially in the USA; and movement to full use of the metric system (centimetre-gram-second system) has been generally slow in English-speaking countries, except in reporting results of laboratory experimentation. Furthermore, we are now being encouraged to move further, to the adoption of the SI system (Systeme Internationale) of units (metre-kilogram-second), which is the most logical of all. In this volume, the metric system is used as the basis, including for operations on the industrial scale, though simultaneous conversion is made back to engineering units where information arose in this system originally. Reference is also made to the corresponding SI units where it is thought to be appropriate, and the important relationships between the various relevant units used at different times are set out in the Appendix. A similar problem arises in the choice of symbols for physical properties and parameters; though a common system is developing, in discussion of

PREFACE Vll

the work of certain authors, this volume also uses the particular symbols as used originally.

Each chapter has been written by an international expert in that particular field. It is therefore to be hoped that the present volume will provide a convenient and readable source of information and reference in the English language for all those interested in the industrial processing of coffee, and in the remaining but important process left to the consumer, i.e. coffee brewing.

R. J. CLARKE R. MACRAE

Contents

Preface .

List of Contributors

Chapter 1 Green Coffee Processing J-C. VINCENT l. Introduction. 2. Dry Processing Method

2.1. Natural drying 2.2. Artificial drying

3. Wet Processing Method 3.1. Receiving 3.2. Pulping. 3.3. Separation/classification. 3.4. Fermentation. 3.5. Washing 3.6. Draining and pre-drying 3.7. Drying of the parchment coffee

4. Curing. 4.1. Redrying 4.2. Cleaning 4.3. Hulling. 4.4. Size grading 4.5. Density sorting 4.6. Colorimetric sorting

5. Storage 6. Handling

References ix

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1 3 3 4 8

10 10 15 17 18 19 19 22 22 22 22 26 27 28 31 32 33

X CONTENTS

Chapter 2 Grading, Storage, Pre-treatments and Blending R. J. CLARKE

I. Introduction. 2. Marketed Grades.

2. I. Systems of specification. 2.2. Liquoring/flavour characteristics 2.3. Bean size and shape 2.4. Defects . 2.5. Colour . 2.6. Roasting characteristics. 2.7. Bulk density 2.8. Crop year

3. Storage 3.1. Storage conditions. 3.2. Isotherms 3.3. Storage stability 3.4. Methods of storage

4. Pre-treatments 4. I. Cleaning and des toning . 4.2. 'Health' coffees

5. Selection and Blending. 5.1. Availability . 5.2. Selection 5.3. Blending methods. References .

Chapter 3 Decaffeination of Coffee S. N. KATZ I. Introduction. 2. Solvent Decaffeination . 3. Water Decaffeination . 4. Supercritical Carbon Dioxide Decaffeination 5. Decaffeination of Roasted Coffee and Extract 6. Caffeine Refining.

References .

Chapter 4 Roasting and Grinding R. J. CLARKE I. Introduction. 2. Process Factors in Roasting.

2. I. Mechanisms and methods 2.2. Chemical changes 2.3. Heat factors . 2.4. Physical changes 2.5. Measurement of roast degree. 2.6. Emission control of organic compounds and chaff.

3. Roasting Equipment 3. I. Horizontal drum roasters

35 35 36 38 39 42 48 48 49 49 49 49 50 50 51 52 52 53 54 54 54 57 57

59 61 64 66 68 69 70

73 73 73 75 79 84 86 87 89 89

CONTENTS

3.2. Vertical fixed drum with paddles 3.3. Rotating bowl 3.4. Fluidised beds 3.5. Pressure operation. 3.6. Roaster ancillaries.

4. Process Factors in Grinding. 4.1. Mechanism of grinding . 4.2. Size analysis . 4.3. Bulk density of ground coffee

5. Grinding Equipment References .

Chapter 5 Extraction R. J. CLARKE I. Introduction. 2. Mechanisms and Methods .

2.1. Methods 2.2. Mechanism of soluble solids extraction. 2.3. Mechanism of volatile compound extraction. 2.4. Compositional factors . 2.5. Balances and rate and productivity factors 2.6. Volatile compound handling.

3. Process Equipment 3.1. Percolation batteries 3.2. Continuous countercurrent screw extractor 3.3. Process control measurements References .

Chapter 6 Drying R. J. CLARKE I. Introduction. 2. Process Factors in Spray-drying

2.1. Methods 2.2. Compositional changes . 2.3. Spray formation 2.4. Spray-air contact . 2.5. Mechanisms of water removal 2.6. Mechanisms of volatile compound retention . 2.7. Fines separation 2.8. Agglomeration

3. Process Factors in Freeze-drying . 3.1. Methods 3.2. Mechanism of water removal. 3.3. Mechanism of volatile compound retention

4. Process Factors in Pre-concentration 4.1. Evaporation . 4.2. Freeze-concentration 4.3. Reverse Osmosis .

xi

93 95 96 97 97 97 97 99

104 104 106

109 110 110 114 115 117 122 134 141 141 142 143 144

147 149 149 150 151 155 156 167 179 180 181 181 182 188 190 190 190 192

xii CONTENTS

5. Process Equipment 192 5.1. Spray driers . 192 5.2. Agglomerators 193 5.3. Evaporators . 194 5.4. Freeze concentrators 194 5.5. Freeze driers. 194 5.6. Other driers . 195 5.7. Process control 195 5.8. Dust and fire hazards 196 References . 197

Chapter 7 Packing of Roast and Instant Coffee 1. Introduction. 2. Packing of Roast Whole Bean Coffee

2.1. Carbon dioxide evolution 2.2. Stability factors 2.3. Types of pack

3. Packing of Roast and Ground Coffee 3.1. Carbon dioxide evolution 3.2. Stability factors 3.3. Types of pack

4. Packing of Instant Coffee 5. Packing Equipment

5.1. Degassing plant 5.2. Roast and ground coffee 5.3. Instant coffee. 5.4. Weight control References .

R. J. CLARKE 201 202 202 206 206 207 207 209 211 215 217 217 218 218 218 219

Chapter 8 Home and Catering Brewing of Coffee G. PICTET I. Introduction. 221 2. Bibliographic Review . 222

2.1. Solid~liquid extraction 222 2.2. Brewing of roast coffee . 223 2.3. Properties of the coffee brew. 230

3. Personal Research 234 3. I. Introduction. 234 3.2. Experimental data. 234 3.3. Discussion of results 238

4. General Conclusions 250 References . 252

Chapter 9 Waste Products M. R. ADAMS and J. DOUGAN 1. Primary Processing: the Production of Green Coffee 257

1.1. Dry or natural processing 257 1.2. Wet processing 259

CONTENTS Xlll

2. Secondary Processing: the Production of Instant Coffee 283 2.1. Coffee grounds 283 2.2. Spent coffee grounds as fuel and feed 286 References 287

Appendix 1. Units 293

1.1. SI base units. 293 1.2. Some SI derived units used in engineering 293 1.3. Some prefixes for SI units 294 1.4. Some conversions of SI and non-SI units 295 1.5. Dimensionless units used 296

2. Symbols for Physical Quantities in Equations 298 3. Abbreviations 298 4. Flavour Terminology . 299 5. Process Engineering Terminology. 300

5.1. Food engineering and unit operations 300 6. Listing of British and International Standards Relating to Coffee 304

Index 305

List of Contributors

M. R. ADAMS

Department of Microbiology, University of Surrey, Guildford, Surrey GU25XH, UK

R. J. CLARKE

Ashby Cottage, Donnington, Chichester, Sussex P020 7PW, UK

J. DOUGAN

Tropical Development and Research Institute, 56--62 Gray's Inn Road, London WCIX 8LU, UK

S. N. KATZ

General Foods Manufacturing Corporation, Maxwell House Division, 1125 Hudson Street, Hoboken, New Jersey 07030, USA

G. PICTET

Linor-Food Development Centre, Nestec Ltd, Orbe, Switzerland

J-c. VINCENT

Institut de Recherches du CaR, du Cacao, Centre Gerdat, Avenue du Val de Mon(ferrand, BP 5035, 34032 Montpellier Cedex, France

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