MODERN DAIRY TECHNOLOGY Volume 2 Advances in Milk Products Second Edition JOIN US ON THE INTERNET VIA WWW, GOPHER, FTP OR EMAil: WWW: http://www.thomson.com GOPHER: gopher.thomson.com A service of I(j)P FTP: ftp.thomson.com EMAIL: [email protected] MODERN DAIRY TECHNOLOGY Volume 2 Advances in Milk Products Second Edition Edited by R. K. Robinson Department of Food Science and Technology, University of Reading, UK BLACKIE ACADEMIC & PROFESSIONAL An Imprint of Chapman & Hoi London· Weinheim . New York· Tokyo· Melbourne· Madras Published by Blackie Academic & Professional, an imprint of Chapman & Hall Chapman & Hall, 2-6 Boundary Row, London SE1 8HN, UK Chapman & Hall GmbH, Pappelallee 3,69469 Weinheim, Germany Chapman & Hall USA, 115 Fifth Avenue, New York, NY 10003, USA Chapman & Hall Japan, ITP-Japan, Kyowa Building, 3F, 2-2-1 Hirakawacho, Chiyoda-ku, Tokyo 102, Japan DA Book (Aust.) Pty Ltd, 648 Whitehorse Road, Mitcham 3132, Victoria, Australia Chapman & Hall India, R. Seshadri, 32 Second Main Road, CIT East, Madras 600035, India Second edition 1993 Reprinted 1996 © 1993 Chapman & Hall Softcover reprint of the hardcover 2nd edition 1996 Typest by Interprint Ltd., Malta ISBN 978-1-4684-8174-7 ISBN 978-1-4684-8172-3 (eBook) DOl 10.1007/978-1-4684-8172-3 Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the UK Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored, or transmitted, in any form or by any means, without the prior permission in writing of the publishers, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to the publishers at the Glasgow address printed on this page. The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made. A Catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data available 8 Printed on acid-free text paper, manufactured in accordance with ANSIINISO Z39.48-1992 (Permanence of Paper). Preface to the Second Edition As with the products and processes described in Volume· I of this book, many of the technical changes associated with, for example, the manufacture of cheeses or fermented milks have been subtle rather than dramatic. Nonetheless, the importance for the dairy industry has often been profound. The market demand for dairy products containing 'health-promoting' cultures is a development that was barely discernible 10 years ago, and yet many manufacturers are now generating a whole range of bio-yoghurts and similar retail items. Similarly, the legislation covering food hygiene has been modified to place additional demands upon manufacturers, a move that has in turn encouraged the further development of analytical methods for quality controL These modifications to manufacturing practices are, along with many others, reflected in this second edition, and I acknowledge with gratitude the enthusiastic co-operation of all the authors associated with this project in bringing their disparate contributions up-to-date. R. K. ROBINSON v Preface to the First Edition Retail sales of most dairy products are still on the increase world-wide, and this expansion is, at least in part, a reflection of the fact that prices have tended to remain at a competitive level. This relative stability has been achieved either through the introduction of major changes in technology, as in the case of the territorial cheeses, or by a massive scale-up of a traditional process like yoghurt making, but whatever the chosen route, the enhanced productivity has been to the benefit of the consumer. Improved methods of product control have also been instru mental in raising the efficiency of the various manufacturing procedures, and the intention of this second volume is to record the current 'state of the art' in respect of the major dairy products. Obviously, processes will continue to become sophisticated, but if this text can provide a back ground to future developments, then the endeavours of the contributors will have been worthwhile. R. K. ROBINSON vii Contents Preface to the Second Edition . v Preface to the First Edition VIJ 1. Manufacture of Yoghurt and Other Fermented Milks R. K. Robinson and A. Y. Tamime 2. Modern Cheesemaking: Hard Cheeses 49 A. Y. Tamime 3. Modern Cheesemaking: Soft Cheeses. 221 M. B. Shaw 4. Developments in Frozen-Products Manufacture 281 H. L. Mitten and J. M. Neirinckx 5. Physical Properties of Dairy Products 331 M. J. Lewis 6. Modern Laboratory Practice - 1: Chemical Analyses 381 T. Andersen, N. Brems, M. M. B¢rglum, S. Kold- Christensen, E. Hansen, 1. H. J¢rgensen and L. Nygaard 7. Modern Laboratory Practice - 2: Microbiological Analyses 417 G. L. Pettipher 8. Technology for the Developing Countries 455 1. T. Homewood and H. J. Hess Index 495 ix list of Contributors Mr T. Anderson A/S N. Foss Electric, 69 Slangerupgade, DK 3400, Hillerod, Denmark. Mr M. M. Borglum A/S N. Foss Electric, 69 Slangerupgade, DK 3400, Hillerod, Denmark. Mr N. Brems A/S N. Foss Electric, 69 Slangerupgade, DK 3400, Hillerod, Denmark. Mr E. Hansen A/S N. Foss Electric, 69 Slangerupgade, DK 3400, Hillerod, Denmark. Dr H. J. Hess Nestec Ltd, Avenue Nestle 55, 1800 Vevey, Switzerland. Mr J. T. Homewood Nestec Ltd, Avenue Nestle 55, 1800 Vevey, Switzerland. Mr J. H. Jorgensen A/S N. Foss Electric, 69 Slangerupgade, DK 3400, Hillerod, Denmark. Mr s. Kold~Christensen A/S N. Foss Electric, 69 Slangerupgade, DK 3400 Hillerod, Denmark. Dr M. J. Lewis Department of Food Science & Technology, University of Reading, Whiteknights, Reading, Berkshire, UK, RG6 2AP. Mr H. L. Mitten Apartment 726, 400 West Butterfield Road, Suite 726, Elmhurst, IL 60126, USA. Mr J. Neirinckx APV Pasilac AS, Pasteurvej, DK 8600 Silkeborg, Denmark. Mr L. Nygaard A/S N. Foss Electric, 69 Slangerupgade, DK 3400, Hillerad, Denmark. xi List of contributors Dr G. L. Pettipher Reading Scientific Services Ltd, The Lord Zuckerman Research Centre, University of Reading, Whiteknights, Reading, Berkshire, UK, RG6 2LA. Dr R. K. Robinson Department of Food Science & Technology, University of Reading, Whiteknights, Reading, Berkshire, UK, RG6 2AP. Mr M. B. Shaw Dairy Crest Ltd, Portsmouth Road, Surbiton, Surrey, UK, KT6 5QL. Dr A. Y. Tamime SAC - Auchincruive, The National College of Food, Land and Envi ronmental Studies, Food Science & Technology Department, Auchin cruive, Ayr, UK. xii Chapter 1 Manufacture of Yoghurt and Other Fermented Milks R. K. Robinson Department of Food Science & Technology, Univeristy of Reading, UK and A. Y.Tamime SAC-Auchincruive, The National College for Food, Land and Environmental Studies, Food Science & Technology Department, Ayr, UK INTRODUCTION Although yoghurt and other fermented milks can be manufactured on a small scale, and with modest levels of technology, the growing demand for products within the industrialised countries has lead to the installa tion of plants capable of handling thousands of litres of milk per day. As a result, sophisticated, automated systems of manufacture are now commonplace, and yet the basic approach to production is still reminis cent of the traditional procedures that have been associated with the peoples of the Middle East for hundreds of years. The reason for this linkage lies in the fact that success with any fermented product lies with the microflora and, in many cases, the microorganisms employed in a modern factory are basically derived from traditional cultures. Obviously, the manufacturers of starter cultures have become heavily involved with the selection of strains with special attributes, but at generic or species level, many of the bacteria enjoy a long association with the dairy industry (Tamime, 1990). Although historical in origin, the association of certain cultures with specific products is now well established, and the link is maintained either by (a) custom, e.g. the characteristic flavour of yoghurt depends, in the main, on the presence of detectable levels of acetaldehyde, a compound released in quantity during the synergistic growth of 2 R. K. Robinson and A. Y. Tamime Lactobacillus delbrueckii subsp. bulgaricus (Lac. bulgaricus) and Streptococcus salivarius subsp. thermophilus (Str. thermophilus); or by (b) legal or non-legal requirements. In most countries, it is usual to insist that yoghurt contains at least a small percentage of Lac. bulgaricus, and similarly that the retail product must contain an 'abundant and viable microflora of starter origin'; products that do not meet these requirements should not be called 'yoghurt'. It is against this background that modern systems for fermented milks have been derived, and as yoghurt remains the most popular item in the group, it is appropriate that its method of production should serve to exemplify the associated industrial processes. PREPARATION OF THE BASIC MIX The overall procedure for the manufacture of yoghurt is shown in Fig. 1, and the first step is the production of the basic mix. Most factories employ liquid milk as the main ingredient, and this material will be delivered, in bulk, employing road tankers. The reception tests applied to such milk, and the standards of hygiene expected in the unloading bays, are similar to those associated with any milk-processing plant (Luck and Gavron, 1990), and assuming that the normal criteria are met, the milk will be transferred to storage silos at < 5°C. Beyond this stage, however, the processing of the milk for yoghurt follows a distinctive pattern of its own. Although there is a definite market for full-fat yoghurts - both natural and fruit yoghurts - the major share of the market is taken with low-fat yoghurts. This trend, while driven in the main by the diet conscious consumer, does allow the manufacturer to market the cream as a separate entity. The next step in manufacture usually involves, there fore, passage of the milk through a centrifugal separator to give a stream of skim-milk (0·5-0·7% fat) and cream. If the manufacturer wishes to produce a medium-fat yoghurt, then some of the separated cream will be fed back into the skim-milk, and automatic monitoring will ensure the constant composition of the final process stream (see Fig. 2). Once the fat content has been standardised, the next stage is to raise the level of milk-solids-non-fat (MSNF), for without this additional protein, the 'gel' produced during the fermentation stage will be thin and 'watery', and prone to syneresis, i.e. separation of free whey from the coagulum