Note the values above must be recorded at the same temperature as v, the velocity of flow. A value of is not particularly high and higher values are recommended. The higher the value, the less difference there will be between the average particle velocity and the highest particle velocity. Also there will be a more uniform particle velocity distribution.

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Gaithersburg, Maryland The author has made every effort to ensure the accuracy of the information herein. However, appropriate information sources should be consulted, especially for new or unfamiliar procedures. It is the responsi- bility of every practitioner to evaluate the appropriateness of a particular opinion in the context of the actual clinical situations and with due considerations to new developments. The author, editors, and the publisher cannot be held responsible for any typographical or other errors found in this book.

Aspen Publishers, Inc. The schematic drawing on the cover shows a typical continuous-flow thermal process with steam injection and expansion cooling. The drawing is adapted with permission from H. ISBN 1. Food—Effect of heat on. Heppell, NJ. Food engineering series Aspen Publishers TP A Wolters Kluwer Company www.

This consent does not extend to other kinds of copying, such as copying for general distribution, for advertising or promotional purposes, for creating new collective works, or for resale. For information, address Aspen Publishers, Inc. We are committed to providing the highest quality information available in the most appropriate format for our customers.

A few years ago it became out of print, and I was asked to con- sider a revised second edition. After thought and discussion with others, it seemed to me that there was insufficient new material to justify a simple revision of the same book. There did, however, seem to be a need to extend the book to cover the ultrahigh-temperature UHT processing of more-viscous food products and of those containing particulates.

I did not feel able to do this myself; by that time I had been away from active work for too long, and my direct experience did not include these newer applications. I suggested that Michael Lewis and Neil Heppell, both of whom I had known for some time, might be interested in writing such a book.

In most respects this is a new and different book. Apart from an extension to viscous and particulate materials, they decided to include material on all continuous-flow heat treatment processes, which include pasteurization as well as UHT processes. Their approach has been that of chemical engineers, and much of the material specific to milk that I included has been omitted to accommodate material applicable to other products.

However, some of the sub- jects covered in my book, particularly relating to UHT heat treatment systems and to aseptic filling methods, have changed little. Parts of my book dealing with these subjects have there- fore been reused with little modification. I hope that their work will be well received and accepted as an important contribution to food-processing literature. I am pleased to have played some part in its inception and to have contributed to it.

Harold dedicated this seminal book to all those who worked on UHT processing and aseptic filling at the National Institute for Research in Dairying NIRD between and and particularly those in the Process Engineering Group, of which he was head for much of the time.

During that period his group did much of the fundamental work on understanding the safety and quality of UHT milk, and his name was known world- wide.

Harold retired in and felt that he had been away from an active work and research environment for too long to undertake the task of revision, so he suggested to the publishers that Neil Heppell and I may wish to tackle it. Our relationship with Harold extends for more than twenty years.

I was introduced to Harold by Reg Scott the author of Cheesemaking Practice shortly after my appointment as a lecturer in the Department of Food Science at University of Reading in Others who followed a similar path were Sami Al-Roubaie, Geoffrey Andrews, Monika Schroder, and Paul Skudder, all of whom have contributed to the further understanding of continuous heat treatment. This helped to develop a good working relationship between NIRD and the university.

Harold also worked with many other international experts on UHT during this period, some of whom spent periods of time studying at the NIRD. Meanwhile, the university obtained an APV Junior UHT plant in , which has been used extensively for teaching, product de- velopment, and research since then. UHT activity at the university was summarized in a recent article Lewis, M. Therefore, we proposed a more ambitious project, ex- tending the basic format of the book to cover continuous heat treatment in its wider aspects.

Three major areas were identified to provide a wider coverage. The first was to extend the range of food products covered beyond milk products alone. This is a simple aim to state, but one that in practice is much more difficult to achieve, as the bulk of the published research work on continuous heat treatment still relates to milk and milk-based products.

This probably stems from milk being widely available, cheap, and ex- tremely nutritious. The reason it is so nutritious is its chemical complexity, which in turn leads to its being both a very difficult and fascinating product to study.

However, in contrast, the commercial reality is that there is now a much wider range of aseptic products available to the consumer, although the relevant technical information on such matters as formulations and processing conditions is not so easy to find in the public domain. There would appear to be plenty of scope for further experimental work on these products. This has been particu- larly noticeable in the chapters on sterilization, storage, and fouling and cleaning, which are predominantly milk-based.

Although this book deals predominantly with milk and milk- based products, it also covers a wider range of products than any other currently on the market. The second aspect involved the realization that many of the products now processed are considerably more viscous than are milk and cream, and some of them contain discrete par- ticles deliberately added and not present as sediment.

It was felt important to cover the heat treatment of more-viscous fluids, where streamline flow conditions are likely to prevail, as well as the thornier problem of heat-treating products containing particles, ideally ensuring uniform heating of the solid and liquid phases. It became necessary to cover the underlying principles and problems in more general terms without reference to specific products. The third important aspect was to extend the coverage to incorporate pasteurization and heat treatments designed to extend further the shelf life of pasteurized products.

In fact, pasteurized products are more widespread than sterilized products in many countries. It was felt that this could be most effectively done by positioning the processes of pasteurization and sterilization next to each other to emphasize further their similarities and the differences.

This was also felt to be the most appropriate place to discuss the heat treatment of acidic products, fruit juices in particular, and strategies for extending the keeping quality of pas- teurized products. We have aimed to produce a book that will give a clear explanation of the principles involved in continuous heat treatment processes. The emphasis throughout is on product safety and quality. To fully understand these issues involves integrating a number of impor- tant scientific disciplines covering the physical aspects of foods: the transfer of energy and the effects of heat on the chemical, biochemical, and sensory characteristics; and the prob- lems inherent in dealing with biological raw materials.

How best to arrange the material to achieve these objectives was a major problem. There is a detailed introductory chapter, which sets the scene and covers, in some detail, the physical properties of foods and their influence on thermal processing operations.

It is our experience that these important aspects are often overlooked in courses on heat processing, despite their considerable influence on the overall process itself. This is followed by chapters that cover the general principles of reaction kinetics, the different types of heat exchangers, and the problems encountered with viscous and particu- late matter, as these will be appropriate to both pasteurization and sterilization.

Following these are specific chapters on pasteurization and sterilization, where there is considerable detail, mainly on milk but also on a number of other products. To complete the book, specific chapters are devoted to aseptic packaging, storage, fouling and cleaning, and quality assur- ance. This layout should help the reader who wishes to explore specific topics in depth. We have taken care to ensure that the book is well cross-referenced and indexed, which will help the reader who wishes to browse.

We hope that this book will be particularly useful to undergraduate and postgraduate stu- dents of food science and technology, and to biotechnologists and engineers who need to heat and cool biological raw materials. We believe that it will provide a useful reference source to those in the industry and pro- vide a focus for gaining a better understanding of the factors influencing safety and quality.

We believe that one of the strengths of the book is the combination of theoretical knowledge derived from the considerable research output in the subject area with our practical experi- ence of heat processing. We have tried to make our explanations as clear as possible, espe- cially so when interpreting results from those articles where it was not too clear what was really intended.

There is a great deal of interest rightly so in alternative technologies and processes for pasteurizing and sterilizing foods. Unfortunately, most articles that deal with these subjects ignore the fact that they have to compete against heat treatment, which is a very effective, convenient, and energy-efficient method of processing foods. In fact, the application of heat in higher temperatures-shorter times HTST pasteurization and UHT sterilization are two well-established minimum processes.

One thing appreciated at an early stage in the writing of this book is that no single book on thermal processing can cover in "academic depth" such a wide and diverse subject area. In fact, many books have been written on thermal process- ing. We have aimed to ensure that this one will give a good balance between the engineering aspects and problems and the chemical, biochemical, and microbiological issues that have to be considered to produce foods that are both safe and of a high quality.

Finally, returning to Harold Burton, in brewing technology there is a process known as "Burtonizing" the water, which ensures water used for beer production has a composition similar to that found in Burton-on-Trent, one of the great brewing centers in the United Kingdom.

It could well be argued, considering his enormous contribution to the subject area, that the term Burtonizing the milk would be synonymous with UHT treatment.


Continuous thermal processing of foods Pasteurization and UHT Sterilization

The food products covered now include soups, sauces, fruit juices, and other beverages, in addition to milk and milk products. Pasteurization, sterilization, and aseptic processing are all discussed, with emphasis on the underlying principles and problems of heat treatment of more viscous fluids, where streamline flow conditions are likely to prevail, and of products containing particles. Pasteurization and heat treatments designed to further extend the shelf life of pasteurized products are also discussed, and the pasteurization and sterilization processes are compared to highlight similarities and differences. Throughout, factors influencing the safety and quality of heated foods are emphasized. This book contains over illustrations and 50 tables, as well as extensive cross-referencing and a comprehensive reference section. Reviews "Lewis and Heppell have provided a review of pasteurisation and UHT processes that is well organised and built on a foundation of engineering and thermobacteriological principles. The literature is thoroughly covered and clearly summarised.





Continuous Thermal Processing of Foods: Pasteurization and UHT Sterilization


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