Dairytechnolog yi nth etropic s and subtropics J.C.T. van den Berg Pudoc Wageningen 1988 J.C.T.va n den Berg graduated as a dairy technologist from Wageningen Agricultural University in 1946,an d then worked for the Royal Netherlands Dairy Federation (FNZ). From 1954t o 1970 he was dairy advisor for milk and milk products at the Ministry of Agriculture and Fisheries. Thereafter, he worked for the International Agricultural Centre, Wageningen, on assignments concerning dairy development and dairy technology in many countries inAfrica , Asia and Latin America; heha s lived and worked inCost a Rica, Pakistan and Turkey. From 1982unti l his retire­ ment, he was a guest worker at Wageningen Agricultural University, where he lectured on production, marketing and processing of milk in tropical and subtropical countries. CIP-DATA KONINKLIJKE BIBLIOTHEEK, DEN HAAG Berg, J.C.T. van den Dairy technology in the tropics and subtropics / J.C.T. van den Berg. - Wageningen : PUDOC. - 111. With index, ref. ISBN 90-220-0927-0 bound SISO 633.9 UDC 637.1(213) NUGI 835 Subject headings: dairy technology ; tropics / dairy technology ; subtropics. ISBN 90 220 0927 0 NUGI 835 © Centre for Agricultural Publishing and Documentation (Pudoc), Wageningen, the Nether­ lands, 1988. No part of this publication, apart from bibliographic data and brief quotations embodied in critical reviews,ma y bereproduced , re-recorded or published inan y form including print, photo­ copy, microfilm, electronic or electromagnetic record without written permission from the pub­ lisher Pudoc, P.O. Box 4, 6700 AA Wageningen, the Netherlands. Printed in the Netherlands. Contents X Preface XI Acknowledgements XII Abbreviations and symbols 1 1 Introduction 3 2 MilMilkk production and milk properties 3 2.1 I Milk production 5 2.2 Composition of milk 8 2.2.1 Water 8 2.2.2 Milk fat 12 2.2.3 Milk proteins 14 2.2.4 Lactose 14 2.2.5 Minerals 14 2.2.6 Citric acid 15 2.2.7 Vitamins 15 2.2.8 Enzymes 17 2.2.9 Other components of milk 20 2.3 Some physical properties of milk 24 2.4 Micro-organisms in milk 25 2.4.1 Bacteria, yeasts and moulds 29 2.4.2 Living conditions of micro-organisms 34 2.4.3 Reproduction of micro-organisms 37 2.5 Milk products and human health 39 2.6 Nutritive value of milk and milk products 40 2.6.1 Milk proteins 41 2.6.2 Milk fat 41 2.6.3 Lactose 42 2.6.4 Minerals 43 2.6.5 Vitamins 45 2.6.6 Comparison between human milk and the milk of mammals VI CONTENTS 47 3 Milk handling on the farm 47 3.1 Preventing milk from being contaminated 49 3.2 Quality of raw milk 50 3.2.1 Appearance of milk 50 3.2.2 Taste and flavour of raw milk 51 3.2.3 Cleanliness of milk 52 3.3 Keeping quality of milk 53 3.4 Cooling of milk 55 3.4.1 Systems of cooling 61 3.4.2 Application of the various systems 62 3.4.3 Capacity of the cooling equipment 63 3.5 Alternative systems of preservation 65 3.6 Milk collection 69 4 Auxiliaries 69 4.1 Electricity 70 4.2 Water 72 4.3 Hot water and steam 75 4.4 Refrigeration 79 4.5 Automation and alternative energy supply 80 4.6 Dairy effluents 82 5 Reception and pretreatment of milk 82 5.1 Reception and storage 82 5.1.1 Intake of milk in cans 87 5.1.2 Intake of milk from tankers 88 5.1.3 Storage of raw milk 88 5.2 Platform sampling and testing of milk 88 5.2.1 Acceptability of milk 90 5.2.2 Composition of milk 90 5.2.3 Hygienic quality of milk 91 5.2.4 Adulteration of milk 92 5.3 Pretreatment of milk 92 5.3.1 Clarification 93 5.3.2 Cream separation 97 5.3.3 Homogenization 98 5.3.4 Standardization 100 5.3.5 Centrifugal homogenization and removal of bacteria 102 5.4 Manufacture of reconstituted and recombined products 102 5.4.1 Reconstituted milk 103 5.4.2 Recombined milk 103 5.4.3 Toned milk 104 5.4.4 Raw materials and water CONTENTS VII 105 5.4.5 The reconstitution process 105 5.4.6 Reconstitution systems 107 5.4.7 The recombining process 107 5.4.8 Recombined liquid milk and fermented milk products 108 5.4.9 Recombined concentrated and dried products 115 6 Heat treatment of milk and processing of liquid milk 115 6.1 Objectives of heat treatment 117 6.2 Systems of heat treatment 117 6.2.1 Holder systems 117 6.2.1.1 Vat pasteurization 118 6.2.1.2 In-package heat treatment 123 6.2.1.3 Advantages and disadvantages of the holder system 124 6.2.1.4 Continuous process of in-bottle sterilization 125 6.2.2 Continuous-flow systems 126 6.2.2.1 Continuous-flow pasteurizers 129 6.2.2.2 Continuous-flow sterilizers 132 6.3 Heat treatment by irradiation 133 6.4 Retail packaging of milk and liquid milk products 133 6.4.1 Distribution of loose milk or packaged milk 134 6.4.2 Packaging of milk 142 6.5 Quality and keeping quality of liquid milk 142 6.5.1 Flavours 144 6.5.2 Sediment 145 6.5.3 Bacteriological defects 149 7 Fermented milks 149 7.1 Origin of fermented milks 152 7.2 Cultures and starters 152 7.2.1 Flora of cultures and starters 153 7.2.2 Production and availability of cultures and starters 155 7.2.3 Low-activity cultures and starters 157 7.3 Types of fermented milk 158 7.3.1 Bulgarian milk 158 7.3.2 Acidophilus milk 159 7.3.3 Alcohol-fermented milks; kefir and koumiss 162 7.3.4 Buttermilk 164 7.3.5 Yogurt and yogurt-like products 169 7.3.6 Other cultured milk products 171 8 Butter and ghee 171 8.1 Definition and description of butter 172 8.2 Manufacture of butter VIII CONTENTS 172 8.2.1 Traditional methods of butter making 175 8.2.2 Industrial manufacture of butter 182 8.2.3 Continuous butter making 183 8.2.4 Direct souring of butter 183 8.2.5 Fat losses and butter yield 184 8.3 Quality of butter i86 8.4 Definition and description of ghee 186 8.5 Manufacture of ghee 186 8.5.1 Indigenous milk-butter process 187 8.5.2 Cream-butter process 188 8.5.3 Direct cream process 189 8.5.4 Butterfat losses 189 8.6 Quality of ghee 192 8.7 Anhydrous milk fat 194 9 Cheese 194 9.1 Definition and description of cheese 197 9.2 Principles of cheese making 197 9.2.1 Preparation of the milk 199 9.2.2 Coagulation of the milk 200 9.2.2.1 Acid-coagulated cheese 201 9.2.2.2 Enzyme-coagulated cheese 204 9.2.3 Separation of whey to obtain curd 208 9.2.4 Processing of the curd 213 9.2.5 Ripening of cheese 215 9.2.6 Special processes of preservation 218 9.3 Cheese additives 219 9.4 Processed cheese and whey cheese 219 9.4.1 Processed cheese 220 9.4.2 Whey cheese and other whey products 223 10 Concentrated and dried products 223 10.1 Concentrated milk products 223 10.1.1 Indigenous products 225 10.1.2 Evaporated and condensed milks 226 10.1.2.1 Concentration of milk 230 10.1.2.2 Evaporated milk 231 10.1.2.3 Condensed milk 233 10.2 Dried products 233 10.2.1 Milk powder 233 10.2.1.1 Roller or drum drying 236 10.2.1.2 Spray drying 237 10.2.1.3 Freeze drying CONTENTS IX 238 10.2.2 Properties and quality of milk powder 242 10.2.3 Whey powder and buttermilk powder 244 11 Cream, flavoured milk and edible ices 244 11.1 Cream 246 11.2 Flavoured milks 247 11.3 Edible ices 251 12 Testing of milk and payment for milk 251 12.1 Testing of milk 251 12.1.1 Sampling and treatment of samples 252 12.1.2 Bacteriological tests 252 12.1.2.1 Dye reduction test 254 12.1.2.2 Standard plate count 255 12.1.2.3 Coliform count 256 12.1.3 Physico-chemical tests 259 12.1.4 Tests for the determination of residues 260 12.1.5 Tests for the composition of milk 264 12.1.6 Tests to indicate adulteration of milk 265 12.2 Payment for milk 266 13 Sanitization 266 13.1 Principles of sanitization 266 13.1.1 Pre-rinse 267 13.1.2 Cleaning 270 13.1.3 Sterilization 272 13.1.4 Drying the equipment 273 13.2 Sanitization at farm level 277 13.3 Sanitization in collection centres and dairy plants 281 Index Preface The burgeoning of dairy sciencean d dairy technology has led to an enormous number of articles and books being published on these topics. Unfortunately, all, or at least most of them, focus on one ortw osubject s only.Thi s form of specialization has divert­ ed attention from the interaction of the various technical and technological aspects of milk handling, milk processing and related subjects. Therei sa grea t need for a hand­ book covering the basicso f dairy chemistry, physicsan d microbiology, in combination with the handling of milk at farm level, the collection and quality control of milk, and the processing of milk into various products, especially for countries inth e tropics and subtropics that are developing a dairy industry.