FOOD PROCESSING TECHNOLOGY Principles and Practice Second Edition P. Fellows Director, Midway Technology and Visiting Fellow in Food Technology at Oxford Brookes University Published by Woodhead Publishing Limited Abington Hall, Abington Cambridge CB1 6AH, England Published in North and South America by CRC Press LLC 2000 Corporate Blvd, NW Boca Raton FL 33431 USA First edition 1988, Ellis Horwood Ltd Second edition 2000, Woodhead Publishing Limited and CRC Press LLC ß 2000, P. Fellows The author has asserted his moral rights. Conditions of sale This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. Reasonable efforts have been made to publish reliable data and information, but the author and the publishers cannot assume responsibility for the validity of all materials. 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Woodhead Publishing Limited ISBN 1 85573 533 4 CRC Press ISBN 0 8493 0887 9 CRC Press order number: WP0887 Cover design by The ColourStudio Project managed by Macfarlane Production Services, Markyate, Hertfordshire Typeset by MHL Typesetting Ltd, Coventry, Warwickshire Printed by TJ International, Cornwall, England For Wen Contents Acknowledgements . ........................................................ xvii Glossary ...................................................................... xix List of symbols ............................................................... xxvii List of acronyms . ........................................................ xxx Introduction . ............................................................... 1 The food industry today . .............................................. 1 About this book . ........................................................ 3 Note on the second edition . .............................................. 4 PART I BASIC PRINCIPLES 7 1 Properties of foods and processing theory . ......................... 9 1.1 Properties of liquids, solids and gases . ......................... 9 1.1.1 Density and specific gravity ................................ 10 1.1.2 Viscosity . .............................................. 13 1.1.3 Surface activity . ....................................... 14 1.1.4 Rheology and texture ....................................... 16 1.2 Material transfer . .............................................. 18 1.3 Fluid flow . ........................................................ 21 1.3.1 Fluid flow through fluidised beds . ......................... 26 1.4 Heat transfer ........................................................ 26 1.4.1 Energy balances . ....................................... 27 1.4.2 Mechanisms of heat transfer ................................ 27 1.4.3 Sources of heat and methods of application to foods . 37 1.4.4 Energy conservation . ....................................... 38 1.4.5 Effect of heat on micro-organisms ......................... 40 1.4.6 Effect of heat on nutritional and sensory characteristics . 43 1.5 Water activity . .............................................. 44 1.5.1 Effect of aw on foods ....................................... 47 1.6 Effects of processing on sensory characteristics of foods . ........ 48 viii Contents 1.6.1 Texture . ................................................... 49 1.6.2 Taste, flavour and aroma . .............................. 49 1.6.3 Colour . ................................................... 50 1.7 Effects of processing on nutritional properties . ............. 50 1.8 Food safety, good manufacturing practice and quality assurance . 52 1.8.1 HACCP . ................................................... 55 1.8.2 Hurdle technology . ..................................... 57 1.9 Acknowledgements . ............................................ 59 1.10 References . ................................................... 59 2 Process control . ................................................... 63 2.1 Automatic control . ............................................ 64 2.1.1 Sensors . ................................................... 65 2.1.2 Controllers . ............................................ 70 2.2 Computer-based systems . ..................................... 72 2.2.1 Programmable logic controllers (PLCs) . ............. 72 2.2.2 Types of control systems . .............................. 74 2.2.3 Software developments ..................................... 75 2.2.4 Neural networks ............................................ 77 2.3 Acknowledgements . ............................................ 78 2.4 References . ................................................... 78 PART II AMBIENT-TEMPERATURE PROCESSING 81 3 Raw material preparation . ............................................ 83 3.1 Cleaning . ................................................... 83 3.1.1 Wet cleaning . ............................................ 84 3.1.2 Dry cleaning . ............................................ 85 3.1.3 Removing contaminants and foreign bodies . ............. 85 3.2 Sorting ............................................................. 87 3.2.1 Shape and size sorting ..................................... 88 3.2.2 Colour sorting . ............................................ 92 3.2.3 Weight sorting . ............................................ 93 3.3 Grading . ................................................... 95 3.4 Peeling ............................................................. 95 3.4.1 Flash steam peeling . ..................................... 95 3.4.2 Knife peeling . ............................................ 96 3.4.3 Abrasion peeling . ..................................... 96 3.4.4 Caustic peeling . ............................................ 96 3.4.5 Flame peeling . ............................................ 96 3.5 Acknowledgements . ............................................ 97 3.6 References . ................................................... 97 4 Size reduction . ................................................... 98 4.1 Size reduction of solid foods . ..................................... 99 4.1.1 Theory . ................................................... 99 4.1.2 Equipment . ............................................ 102 4.1.3 Effect on foods . ............................................ 108 Contents ix 4.2 Size reduction in liquid foods (emulsification and homogenisation) 110 4.2.1 Theory . .............................................. 110 4.2.2 Equipment . .............................................. 112 4.2.3 Effect on foods . ....................................... 114 4.3 Acknowledgements . .............................................. 116 4.4 References . ........................................................ 116 5 Mixing and forming . .............................................. 118 5.1 Mixing . ........................................................ 118 5.1.1 Theory of solids mixing . ................................ 119 5.1.2 Theory of liquids mixing . ................................ 122 5.1.3 Equipment . .............................................. 125 5.1.4 Effect on foods . ....................................... 132 5.2 Forming . ........................................................ 132 5.2.1 Bread moulders . ....................................... 134 5.2.2 Pie and biscuit formers . ................................ 134 5.2.3 Confectionery moulders . ................................ 138 5.3 Acknowledgements . .............................................. 139 5.4 References . ........................................................ 139 6 Separation and concentration of food components . .................. 140 6.1 Centrifugation . .............................................. 141 6.1.1 Theory . .............................................. 141 6.1.2 Equipment . .............................................. 142 6.2 Filtration . ........................................................ 146 6.2.1 Theory . .............................................. 146 6.2.2 Equipment . .............................................. 149 6.3 Expression . ........................................................ 150 6.3.1 Theory . .............................................. 150 6.3.2 Equipment . .............................................. 151 6.4 Extraction using solvents . ....................................... 153 6.4.1