Dairy Ingredients for Food Processing E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 1309

Veröffentlichungsjahr: 2010

Beschreibung

The objective of this book is to provide a single reference source for those working with dairy-based ingredients, offering a comprehensive and practical account of the various dairy ingredients commonly used in food processing operations. The Editors have assembled a team of 25 authors from the United States, Australia, New Zealand, and the United Kingdom, representing a full range of international expertise from academic, industrial, and government research backgrounds. After introductory chapters which present the chemical, physical, functional and microbiological characteristics of dairy ingredients, the book addresses the technology associated with the manufacture of the major dairy ingredients, focusing on those parameters that affect their performance and functionality in food systems. The popular applications of dairy ingredients in the manufacture of food products such as dairy foods, bakery products, processed cheeses, processed meats, chocolate as well as confectionery products, functional foods, and infant and adult nutritional products, are covered in some detail in subsequent chapters. Topics are presented in a logical and accessible style in order to enhance the usefulness of the book as a reference volume. It is hoped that Dairy Ingredients for Food Processing will be a valuable resource for members of academia engaged in teaching and research in food science; regulatory personnel; food equipment manufacturers; and technical specialists engaged in the manufacture and use of dairy ingredients. Special features: * Contemporary description of dairy ingredients commonly used in food processing operations * Focus on applications of dairy ingredients in various food products * Aimed at food professionals in R&D, QA/QC, manufacturing and management * World-wide expertise from over 20 noted experts in academe and industry

Leseprobe

Table of Contents

Cover

Table of Contents

Half title page

Title page

Copyright page

Contributors

Preface

Chapter 1 Dairy Ingredients for Food Processing: An Overview

Introduction

Milk and Dairy Processing

Fluid Milk Products

Cultured/Fermented Dairy Products

Cheese

Whey Products

Casein and Caseinates

Milk Protein Concentrate

Trends in Availability and Use of Major Dairy Ingredients

Chapter 2 Chemical, Physical, and Functional Characteristics of Dairy Ingredients

Milk

Dairy Ingredients

Milk Components and Other Definitions

Chemical Properties of Milk

Factors Affecting Composition, Quality, and Safety of Milk

Physical Properties of Milk

Functional Properties of Milk

Functional Dairy Ingredients for Food Applications

Chapter 3 Microbiological Aspects of Dairy Ingredients

Raw Milk

Raw Milk Safety

Pasteurized Milk

Cream

Butter

Buttermilk

Cheese

Yogurt

Probiotic Cultures

Concentrated Milk

Dried Milk Powders

Ice Cream

Chapter 4 Processing Principles of Dairy Ingredients

Introduction

From Farm to Factory

Storage of Raw Milk

Overview of Processing Equipment in a Dairy Plant

Chapter 5 Concentrated Fluid Milk Ingredients

Introduction

Composition of Liquid or Fluid Milk and Market Milk

Changes Caused by Concentrating Milk

Historical Perspective for Evaporated and Condensed Milks

Types of Evaporated and Sweetened Condensed Milks

Technologies for Manufacture of Condensed and Evaporated Milks

Vapor Recompression Evaporators

Process for Manufacture of Evaporated Milk

Spoilage of Evaporated Milk

Manufacture of Sweetened Condensed Milk

Dulce de Leche

Defects in Sweetened Condensed Milk

Recombined Evaporated and Sweetened Condensed Milk

Quality Assessment

Membrane Concentration Technologies

Other Uses of Concentrated Dairy Products

Chapter 6 Dry Milk Ingredients

Introduction

Milk Powder Processing

Properties of Milk Powders

Applications of Milk Powders

Specialized Milk Powders

Conclusion

Chapter 7 Casein, Caseinates, and Milk Protein Concentrates

Introduction

Chemistry of Caseins

Casein Products

Caseinates

Milk Protein Concentrates

Functional Properties and Applications

Solubility/Hydration

The Future

Chapter 8 Whey-based Ingredients

Introduction

Whey Sources and Composition

Processing Techniques

Ion Exchange (Protein Isolation and Fractionation)

Whey Products and Ingredients

Functional Properties of Whey Protein Concentrates

Biological Properties

Lactose Processing, Products, and Derivatives

Acknowledgements

Chapter 9 Butter and Butter Products

Introduction

Butter Manufacture and Properties

Principles of Butter Making

Butter Making Technology

Concentrated Forms of Butter

Application of Milk Fat in Products

Quality Assurance of Milk Fat Products and Spreads

Chapter 10 Principles of Cheese Technology

Introduction

Definitions

Classification of Natural Cheeses

Principles of Cheese Making

Mechanization in the Cheese Industry

Packaging Cheese

Chapter 11 Manufacturing Outlines and Applications of Selected Cheese Varieties

Introduction

Natural Cheeses

Process Cheese

Cold-pack or Club Cheese

Cheese Substitutes/Analogs

Applications in Foods

Chapter 12 Enzyme-modified Dairy Ingredients

Introduction

Protein Modification

Lipid Modification

Ingredients Involving Proteolysis and Lipolysis

Chapter 13 Fermented Dairy Ingredients

Introduction

Microflora of Milk Fermentation

Fermented Dairy Products

Chapter 14 Functional Ingredients from Dairy Fermentations

Introduction

Functional Bio-ingredients: Live Cultures

Biopreservatives: Live Protective Cultures

Functional Bio-ingredients: Microbial Metabolites

Chapter 15 Dairy-based Ingredients: Regulatory Aspects

Introduction

Product Identity, Nutritional Labeling, and Allergen Declaration

Current Good Manufacturing Practices, Dairy Hazard Analysis and Critical Control Points, and Pasteurized Milk Ordinance

Food Additives and “Generally Recognized as Safe”

New Ingredient Approval Process

Conclusions

Chapter 16 Nutritive and Health Attributes of Dairy Ingredients

Introduction

Milk and Milk Products as Functional Foods

Chapter 17 Dairy Ingredients in Dairy Food Processing

Introduction

Shelf-stable Powdered Products

Frozen Desserts

Fluid Dairy Products: Refrigerated and Shelf-stable

Cultured Dairy Foods

Refrigerated and Shelf-Stable Ready-to-Eat Desserts/Snacks

Chapter 18 Dairy Ingredients in Bakery, Snacks, Sauces, Dressings, Processed Meats, and Functional Foods

Bakery Products

Cheese and Cheese Products

Snack Foods

Cheese and Dairy Sauces

Processed Meat Products

Functional Foods

Chapter 19 Dairy Ingredients in Chocolate and Confectionery Products

Chocolate Confectionery

Compound Coatings

Sugar Confectionery

Conclusion

Chapter 20 Dairy Ingredients in Infant and Adult Nutrition Products

Introduction

Infant Nutrition

Adult Nutrition

Technologies for Emerging Nutritional Needs

The Future

Product Functionality

Manufacturing Considerations

Conclusion

Acknowledgement

Index

Dairy Ingredients for Food Processing

Edition first published 2011

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Library of Congress Cataloging-in-Publication Data

Dairy ingredients for food processing / edited by Ramesh C. Chandan, Arun Kilara.

p. cm.

 Includes bibliographical references and index.

 ISBN 978-0-8138-1746-0 (hardback)

 ISBN 978-0-4709-5912-1 (ebk)

 1. Dairy processing. 2. Dairy products. 3. Dairy microbiology. I. Chandan, Ramesh C. II. Kilara, Arun.

 SF250.5.D34 2011

 637–dc22

2010040943

ISBN 9780813817460

eISBN 9780470959077

A catalog record for this book is available from the U.S. Library of Congress.

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Contributors

Mary Ann Augustin, PhD

Chapters 6 and 7

CSIRO Food and Nutritional Sciences

671 Sneydes Road

Werribee, Victoria 3030, Australia

Phone: [phone]

[email protected]

Jeffery Baxter, PhD

Chapter 20

Abbott Laboratories

Department 105220, Building RP3-2

3300 Stelzer Road

Columbus, Ohio 43219, USA

Phone: [phone]

[email protected]

Jorge Bouzas, PhD

Chapter 19

The Hershey Company

Technical Center, 1025 Reese Avenue

PO Box 805

Hershey, Pennsylvania 17033, USA

Phone: [phone]

[email protected]

Ramesh C. Chandan, PhD

Chapters 1, 10, 11, 12, 16, 17, and 18

1364 126th Avenue NW

Minneapolis, MN 55448-4004, USA

Phone: [phone]

[email protected]

Phillip Terence Clarke, PhD

Chapter 6

CSIRO Food and Nutritional Sciences

671 Sneydes Road

Werribee, Victoria 3030, Australia

Phone: [phone]

[email protected]

Steven Dimler

Chapter 20

Abbott Laboratories

Department 105220, Building RP3-2

3300 Stelzer Road

Columbus, Ohio 43219, USA

Phone: [phone]

[email protected]

John Donaghy, PhD

Chapter 3

Agri-Food and Biosciences Institute

Newforge Lane

Belfast, Northern Ireland BT9 5PX, UK

Phone: [phone]

[email protected]

Nana Y. Farkye, PhD

Chapter 5

Dairy Products Technology Center

California Polytechnic State University

San Luis Obispo, CA 93407-0251, USA

Phone: [phone]

[email protected]

Anna M. Fearon, PhD

Chapter 9

Food Chemistry Branch

Agri-Food and Biosciences Institute

New Forge Lane

Belfast, Northern Ireland, BT9 5PX, UK

Phone: [phone]

[email protected]

Lilian de Barros Ferreira, PhD

Chapter 8

Senior Research Engineer

Fonterra Research Centre

Private Bag 11029, Dairy Farm Rd

Palmerston North, New Zealand 4442

Phone: [phone]

[email protected]

Yacine Hemar, PhD

Chapter 7

Food Physics, Chemistry Department

University of Auckland

Private Bag 92019,

Auckland, New Zealand

Phone: [phone], Ext. 89676

[email protected]

Steven Hess, PhD

Chapter 19

The Hershey Company

Technical Center, 1025 Reese Avenue

PO Box 805

Hershey, Pennsylvania 17033, USA

Phone: [phone]

[email protected]

Lee M. Huffman, PhD

Chapter 8

Science Group Leader, Food Solutions

The New Zealand Institute of Plant & Food Research Limited

Private Bag 11 600, Palmerston North 4442, New Zealand

Physical Address: Plant & Food Research Palmerston NorthFood Industry Science Centre, Fitzherbert Science Centre

Batchelar Rd, Palmerston North, New Zealand

Phone: [phone]

[email protected]

www.plantandfood.com

Rohit Kapoor, PhD

Chapters 10 and 11

Bongards’ Creameries

13200 County Road 51

Norwood, Minnesota 55368, USA

Phone: [phone]

[email protected]

Kasipathy Kailasapathy, PhD

Chapters 2, 13

School of Natural Sciences

Centre for Plant and Food Sciences

University of Western Sydney

DC, Locked Bag 1797

South Penrith, New South Wales 1797 Australia

Phone : [phone]

[email protected]

Arun Kilara, PhD

Chapters 4 and 12

Nutri+Food Business Consulting

117 Westside Drive

Chapel Hill, North Carolina 27516-4431, USA

Phone: [phone], office; [phone], home

Cell phone: [phone]

Website: www.nfbconsultants.com

[email protected]

Christine Oliver, PhD

Chapter 7

CSIRO Food and Nutritional Sciences

671 Sneydes Road

Werribee, Victoria 3030, Australia

Phone: [phone]

[email protected]

Dilip A. Patel, PhD

Chapter 15

Sterling Technology, Inc.

133, 32nd Avenue South

Brookings, South Dakota 57006, USA

Phone: [phone]

[email protected]

Stephanie R. Pritchard, PhD

Chapter 2

University of Western Sydney

DC, Locked Bag 1797

South Penrith, New South Wales 1797 Australia

Phone:[phone]

[email protected]

Nagendra Rangavajala, PhD

Chapter 20

Abbott Laboratories

Department 105220, Building RP3-2

3300 Stelzer Road

Columbus, Ohio 43219, USA

Phone: [phone]

[email protected]

Michael Rowe, PhD

Chapter 3

Agri-Food and Biosciences Institute

New Forge Lane

Belfast, Northern Ireland, BT9 5PX, UK

Phone: [phone]

[email protected]

Junus Salampessy, PhD

Chapter 13

University of Western Sydney

Hawkesbury Campus

Building M1, Room 31

Bourke Street, Richmond, NSW 2753 Australia

Phone: [phone]

[email protected]

Tonya C. Schoenfuss, PhD

Chapter 17

Department of Food Science and Nutrition

University of Minnesota

165, FScN

1334 Eckles Avenue

St. Paul, Minnesota 55108-1038, USA

Phone: [phone]

[email protected]

Shakeel ur-Rehman, PhD

Chapter 5

3162 E. Deerhill Dr

Meridian, ID 83642, USA

Phone: [phone]

[email protected]

Ebenezer R. Vedamuthu, PhD

Chapter 14

332 NE Carmen Place

Corvallis, Oregon 97330, USA

Phone: [phone]

[email protected]

Preface

Dairy Ingredients for Food Pro­cessing includes advances in technology of major dairy ingredients and their uses in the processing of important food products. The objective of this book is to provide an updated applied reference book for professionals engaged in management, research and development, quality assurance, and manufacturing operations in the food industry. It is a single source that provides basic and practical information to understand and work with dairy-based ingredients. The book is designed to present the topics in a convenient, easy-to-follow format. The intended audience consists of technical personnel in the food industry as well as students and teachers in food science at the university level.

Dairy Ingredients for Food Processing gives a comprehensive description of various dairy ingredients commonly used in food processing operations. The editorial team has assembled 25 authors from the United States, Australia, New Zealand, and the United Kingdom to write the chapters. These contributors represent diverse expertise from academia, industry, and government research institutions. The editors intended to ensure current practical information and scientific accuracy to provide potential reference value to all engaged in the product development, processing, and quality assurance disciplines of the food industry. This book is not meant to be a treatise on the subject but presents the basic and applied information in a single source. The authors have presented the topics in a concise, easily understandable style to enhance usefulness of the book.

Information is conveniently grouped to include basic technology associated with the manufacture of dairy ingredients, especially the parameters that affect their performance and functionality in food systems. The applications of commonly available dairy ingredients in the manufacture of food products such as dairy foods, bakery products, processed cheese, processed meat, chocolate as well as confectionery products, functional foods, and infant and adult nutritional products are covered in some detail. Information is conveniently grouped under 20 chapters by multiple authors to provide an international perspective.

The individuality of the authors’ contributions has been protected by the editors to provide both diversity of information and the focus of the authors. The editors have included minor duplication of some material in certain chapters to give readers another perspective on the subject and to maintain continuity and flow of thought of the respective authors. For the convenience of readers, some basic information has been derived from the previously published book Dairy Processing and Quality Assurance (Wiley-Blackwell, 2008).

Chapter 1 provides an overview of the technology of dairy ingredients, and serves as a refresher on the subject. Chapter 2 is devoted to chemical, physical, and functional characteristics of dairy ingredients. The microbiological aspects are given in Chapter 3. To facilitate understanding of the origin of dairy ingredients, the principles of dairy processing are summarized in Chapter 4. Information on concentrated fluid milk ingredients is discussed in Chapter 5. Dry milk ingredients are described in Chapter 6. Other ingredients including casein, caseinates, and milk protein concentrates are dealt with in Chapter 7. Whey-based ingredients are discussed in Chapter 8. Butter and butter products are found in Chapter 9. Natural and process cheese technology and applications are given in Chapters 10 and 11. Enzyme-modified dairy ingredients are discussed in Chapter 12 and fermented dairy ingredients are presented in Chapter 13.

Dairy fermentations have given the food industry novel and natural preservatives for public health safety and extended shelf life of foods. Furthermore, several functional food ingredients have been developed for the food industry from dairy fermentation technologies, which have been described in Chapter 14. The regulatory aspects of dairy ingredients are presented in Chapter 15, whereas their nutritive and health attributes are given in Chapter 16. The use of dairy ingredients in major dairy manufacturing operations is presented in Chapter 17. The applications of dairy ingredients in bakery, snacks, sauces, dressings, processed meats, and functional foods are discussed in Chapter 18. The applications of dairy ingredients in chocolate and confectionery products are presented in Chapter 19, and their use in infant and adult nutritional products is discussed in Chapter 20.

The authors have attempted to support the origin, properties, and functional characteristics of dairy ingredients as well as their applications in the processing of major food products with sound scientific, technological, and engineering principles. The reader should notice a slant toward practical aspects as well.

It is hoped that the contemporary and experience-based information given in Dairy Ingredients for Food Processing will appeal to all the professionals in the food industry, including manufacturers of dairy ingredients. In addition, it is hoped that the book will be a useful resource for members of academia engaged in teaching and research in food science areas, regulatory personnel, food equipment manufacturers, and technical specialists engaged in the manufacture of dairy and food products.

Ramesh C. Chandan, Minneapolis, Minnesota

Arun Kilara, Chapel Hill, North Carolina

Chapter 1

Dairy Ingredients for Food Processing: An Overview

Ramesh C. Chandan

Introduction

Dairy ingredients are important players in the formulation of many food products. The addition of familiar dairy ingredients, widely recognized by the consumer as “natural,” enhances the odds of success of packaged foods in the marketplace. They generally deliver a consumer-friendly label on the package.

Dairy ingredients are derived from fluid milk in the form of cream, butter, condensed milk, dry milk, cheese, and whey products (Olson and Aryana, 2008, Sodini and Tong, 2006). They provide desirable functionality to foods, such as delivery of key nutrients, water management, fat-holding capacity, emulsification capability, viscosity creation, gel formation, and foam generation. In addition, dairy-based ingredients in liquid, concentrated, or dry form confer desirable attributes of texture and flavor to dairy foods, frozen desserts, puddings, processed meat, cereal products, chocolate confections, infant formulas, and an array of dietetic as well as geriatric drinks and bars. In conventional bakery items, dairy ingredients are used in enriched breads, croissants, milk bread, cakes, cookies, and pastries. Figure 1.1 demonstrates the relationship of milk to major dairy ingredients used for food processing.

Figure 1.1. Relationship of dairy ingredients to milk.

Dairy ingredients contribute several critical characteristics associated with a food product. Caseinates impart emulsifying and stabilizing ability. Whey protein concen­trates and isolates give gelling properties and furnish high-quality protein (Kilara, 2008). Similarly, milk protein concentrates provide a base of dietetic products. High-heat nonfat dry milk is reputed to impart water-absorption capacity to baked goods. Lactose-containing dairy ingredients are responsible for desirable brown crust in bread and other bakery items. Enzyme-modified butter and cheese flavor concentrates are used in food products for butter and cheese carryover. Dairy ingredients are important tools for a food developer to create certain desirable attributes in foods. An understanding of the functional properties of dairy ingre­dients allows food technologists to use their potential contributions to meet consumer expectations.

Consumer trends, especially in functional foods (Chandan and Shah, 2007) as well as fast and convenience foods, are shaping the development of new products in the marketplace. More recently, market opportunities have been leveraged in nutraceutical beverages for use as tools for weight management, meal replacement, and geriatric nutritional needs using fluid skim milk, nonfat dry milk, milk protein concentrate, and whey protein concentrate. In addition, coffee-based drinks have provided the consumer with a variety of nutritional and functional drinks.

In the arena of industrial ingredients, dairy plants fabricate convenient, custom-made mixes for food plants for processing of foods. Such practice is currently undertaken for the production of yogurt, ice cream, and confectionery products (Chandan and O’Rell, 2006a; Kilara and Chandan, 2008). Novel ingredients have been developed by applying membrane technology to fractionate milk and whey to enhance their performance in food products. Such ingredients furnish milk protein, milk fat, or milk minerals in food supplements. A new trend involves development of functional ingredients from whey, colostrum, and bioactive peptides from milk proteins, which possess distinct health-promoting attributes (Chandan 2007a and b). Other ingredients are specific metabolites concentrated in fermented milk or whey by the activity of specific dairy cultures. The dried fermented ingredients derived from fermented bases contain active metabolites that are used as natural preservatives to extend shelf life and safety of foods. The enzyme-modified cheeses are cheese flavor concentrates that are widely used in the production of cheese powders, cheese sauces, and process cheese, and in the preparation of fillings for cookies and crackers.

Milk and Dairy Processing

Fluid milk is a basic ingredient in dairy foods, including frozen and refrigerated desserts (Kilara and Chandan, 2008; Chandan and Kilara, 2008)). Many dairy-derived ingredients for use in food processing owe their origin to milk, which is comprised of water and milk solids. Milk solids are comprised of milk fat and milk-solids-not-fat. Figure 1.2 illustrates the gross composition of milk, showing major constituents. The composition of whole milk solids and nonfat solids is shown in Table 1.1.

Table 1.1. Proximate composition of whole milk solids and skim milk solids.

ComponentWhole milk solidsSkim milk/nonfat solidsFat, %29.361.08Protein, casein, %22.2231.18Whey protein, %4.767.53Lactose, %38.1052.15Ash (minerals), %5.568.06

Figure 1.2. Gross composition of pooled raw milk.

Accordingly, incorporation of dairy ingredients in a food adds these constituents to the overall food composition and allows a food developer to leverage their functionality and other attributes in food product development. Chemical, physical, and functional properties of milk are discussed in Chapter 2.

Variations in Milk Composition

It is important to recognize that milk composition varies depending on the breed of the cow, intervals and stages of milking, different quarters of udder, lactation period, season, feed, nutritional level, environmental temperature, health status, age, weather, estrus cycle, gestation period, and exercise (Chandan, 2007a; Kailasapathy, 2008). The variations in major constituents of milk, namely fat, protein, lactose, and minerals, are more noticeable in milk from individual cows. In general, these variations tend to average out and display an interesting pat­tern in commercial milk used by proces­sors. Nevertheless, the seasonal variations in major milk constituents still impact important properties of finished products. In the United States, approximately 10% variation in fat and protein is observed in milk received in July and August (lowest level) as compared to milk delivered in October and November (highest level). Subsequently, the functional contribution of milk proteins (viscosity in yogurt and buttermilk, and curd firmness in cheese manufacture) follows a similar trend. Butter produced in summer is generally softer than that produced from winter milk. Furthermore, cheese yield and whey protein production can be negatively affected by seasonal variations in milk composition.

The concentration of minerals such as chloride; phosphates; and citrates of potassium, sodium, calcium, and magnesium in milk is important in processing, nutritive value, and shelf life of dairy products. Their concentration is less than 1% in milk. Still, they affect heat stability of milk, age-thickening of sweetened condensed milk, feathering of coffee cream, rennin coagulation, and clumping of fat globules on homogenization. All of the minerals considered essential for human nutrition are found in milk (Chandan, 2008d). For nutritive and health attributes of dairy ingredients, see Chapter 16.

Important Quality Factors

From a consumer standpoint, the quality factors associated with milk are appearance, color, aroma, flavor, and mouth feel. The color of milk is perceived by the consumer to be indicative of purity and richness. The white color of milk is due to the scattering of reflected light by the inherent ultramicroscopic particles, namely fat globules, colloidal casein micelles, and calcium phosphate. The intensity of white color is directly proportional to the size and number of particles in suspension. Homogenization significantly increases the surface area of fat globules as a result of breakup of larger globules. Accordingly, homogenized milk and cream appear whiter than non-homogenized counterparts. After the precipitation of casein and fat by the addition of a dilute acid or rennet, whey separates out. The whey possesses a green-yellow color due to the pigment riboflavin. The depth of color varies with the amount of fat remaining in the whey. Lack of fat globules gives skim milk a blue tinge. Physiological disturbances in the cow also make the milk bluer.

Cow’s milk contains the pigments carotene and xanthophylls, which tend to impart golden yellow color to the milk. Guernsey and Jersey breeds produce especially golden yellow milk. Milk from goats, sheep, and water buffalo tends to be much whiter in color because their milk lacks the pigments.

The flavor of milk is critical to its consumer quality criterion. Flavor is an organoleptic property in which both odor and taste interact. The sweet taste of lactose is balanced against the salty taste of chloride, and both are somewhat moderated by proteins. This balance is maintained over a fairly wide range of milk composition, even when the chloride ion varies from 0.06% to 0.12%. Saltiness can be organoleptically detected in samples containing chloride ions exceeding 0.12% and it becomes marked in samples containing 0.15%. The characteristic rich flavor of dairy products may be attributed to the lactones, methyl ketones, certain aldehydes, dimethyl sulfide, and certain short-chain fatty acids. As lactation advances, lactose declines while chlorides increase, so that the balance is slanted toward “salty.” A similar dislocation is caused by mastitis and other udder disturbances. Accordingly, milk flavor is related to its lactose : chloride ratio.

Freshly drawn milk from any mammal possesses a faint odor of a natural scent peculiar to the animal. This is particularly true for the goat, mare, and cow. The cow odor of cows’ milk is variable, depending upon the individual season of the year and the hygienic conditions of milking. A strong “cowy” odor frequently observed during the winter months may be due to the entry of acetone bodies into milk from the blood of cows suffering from ketosis.

Feed flavors in milk originate from feed aromas in the barn; for instance, aroma of silage. In addition, some feed flavors are imparted directly on their ingestion by the animal. Plants containing essential oils impart the flavor of the volatile constituent to the milk. Garlic odor and flavor in milk is detected just one minute after feeding garlic. Weed flavor of chamomile or mayweed arises from the consumption of the weed in mixtures of ryegrass and clover. Cows on fresh pasture give milk with a less well-defined “grassy” flavor, due to coumarin in the grass. A “clovery” flavor is observed when fed on clover pasture, and these taints are not perceptible when dried material is fed. Prolonged ultraviolet radiation and oxidative taints lead to “mealiness,” “oiliness,” “tallowiness,” or “cappy” odor. Traces of copper (3 ppm) exert development of metallic/oxidized taints in milk. Microbial growth in milk leads to off-flavors such as sour, bitter, and rancid. Raw milk received at the plant should not exhibit any off-flavors. Certain minor vola­tile flavor may volatilized off by dairy processing procedures. Various off-flavors and their origins are summarized in Table 1.2.

Table 1.2. Origins and causes of off-flavors in milk and dairy ingredients.

Adapted from Chandan (1997, 2007a)

Raw Milk Quality Specifications

It is essential to set up stringent specifications for quality maintenance for purchasing milk, The specifications involve several parameters as discussed below.

Standard plate count (SPC) is a measure of the total bacteria count, and measures the overall microbiological quality of milk. High SPC can cause reduced shelf life of the finished product and off flavors from enzyme activity and elevated acidity.

Per Pasteurized Milk Ordinance (USDHHS PMO, 2003), the U.S. Federal Grade A Standards allow a maximum of 100,000 CFU/ml for an individual producer and 300,000 CFU in commingled milk. However, some states differ. For example, for an individual producer, the Idaho standard is 80,000 CFU/ml maximum and the Califor­nia standard is 50,000 CFU/ml maximum. It is recommended to set the standard at 50,000 CFU/ml.

Coliform bacteria count is a measure of milk sanitation. High coliform counts reflect poor milking practices and unsatisfactory cleanliness of the dairy operation. Occasion­ally, coliform count may indicate sick cows in smaller herds. Coliform count is an indicator that food poisoning organisms may be present. There are no federal standards for coliform counts in raw milk, but California has a standard for coliform (750 CFU/ml maximum). A recommended standard is 500 CFU/ml.

Laboratory pasteurized count (LPC) is a measure of heat-stable bacteria that may survive pasteurization. It is performed by heat-treating laboratory samples to simulate batch pasteurization at 62.8°C (145°F) for 30 minutes and enumerating the bacteria that survive using the SPC method. High LPC results indicate potential contamination from soil and dirty equipment at the dairy. High LPC causes reduced shelf life of finished products. Bacillus cereus is a common soil microorganism that can survive pasteurization, resulting in a high LPC. There are no federal standards for LPC. However, the California standard for LPC is 750 CFU/ml maximum. A recommended standard is 500 CFU/ml.

Preliminary incubation (PI) count is a measure of bacteria that will grow in refrigerated conditions. The test requires holding the sample at 10°C (50°F) for 18 hours followed by a SPC test. PI type of bacteria are destroyed by pasteurization but can still result in lower quality milk due to enzymatic activity on the protein. High PIs (3- to 4-fold higher than SPCs) are generally associated with inadequate cleaning and sanitizing of either the milking system or cows and/or poor milk cooling.

There are no federal standards for PI counts in raw milk. Because the type of bacteria and the initial count of the SPC may vary, it is not possible to set a numerical standard for this test. A recommended standard is less than two times the SPC count.

Somatic cell count (SCC) is a measure of the white blood cells in the milk. It is used as an indicator of herd health. High SCCs are undesirable because the yield of all cultured products is proportionally reduced, the flavor becomes salty, development of oxidation increases, and it usually relates to higher SPC. Staphylococci and streptococci are heat-tolerant bacteria that normally cause mastitis. Coliform bacteria, which are easily killed by heat, may cause mastitis. The PMO standards allow individual milk not to exceed 750,000 cells/ml. State standards vary. For example, the California standard is 600,000 cells/ml maximum. A recommended standard is 500,000 cells /ml.

Titratable acidity (TA) is a measure of the lactic acid content of milk. High bacteria counts produce elevated lactic acid levels as the bacteria ferment lactose. The normal range of TA in fresh milk is 0.13% to 0.16%. Elevated temperatures for an extended time allow the bacteria to grow and generate a higher TA value. Lower values may indicate the presence of chemicals in the milk. A recommended standard is 0.13% to 0.17% TA.

Temperature According to the PMO standard, the temperature of milk must never exceed 7°C (45°F). A recommended standard is 5°C (40°F) or less.

Flavor is an important indicator of quality, as stated earlier. The milk should be fresh and clean with a creamy appearance. Elevated bacteria counts can produce off-flavors (for example, acid, bitter). Feed flavors may vary from sweet to bitter and indicate the last items in a cow’s diet, such as poor feed, weeds, onion, or silage. Elevated somatic cell counts make milk taste salty and watery. Water in the milk gives it a watery taste. Dirty, “barny,” and “cowy” flavors occur from sanitation conditions and air quality at the dairy farm. Oxidized or rancid flavors occur from equipment operation and handling.

There are no federal standards for flavor. All receiving plants should flavor milk for defects before accepting it.

A recommended standard is that no off-flavor exists.

Appearance is not a measured criterion but for indications of quality it is as important as flavor. There are no federal standards for appearance. Most receiving plants must note any color or debris defect in the milk before accepting it. A recommended standard is “White, clean, no debris, and filter screen of 2 or less (sediment test).”

Antibiotics and other drugs may not be present in milk. All raw milk must conform to the PMO Grade A regulations (Frye, 2006). To be considered organic, no milk can be used from a cow that has been treated with antibiotics without a 12-month holding period following treatment. For conventional milk, a treated cow will be withheld from the milking herd for about 5 days.

Added water is an adulteration. Testing the freezing point of milk using a cyroscope indicates if abnormal amounts of water exist in the load. In most states it is illegal to have a freezing point above −0.530° Hortvet scale. A recommended standard should be −0.530° Hortvet or less.

Sediment is measured by drawing 1 pint of sample through a cotton disk and assigning a grade of 1 (good) to 4 (bad) to the filter. A grade of 1 or 2 is acceptable. A processor also may monitor for sediment by screening the entire load through a 3-inch mesh filter at the receiving line. There are no federal standards. Most receiving plants should require a filter grade of 1 or 2, although a 3 may be accepted.

A recommended standard is “No excessive material in a 3-inch sani-guide filter.”

Fat and milk-solids-not-fat (MSNF) have FDA standards of identity for milk of 3.25% fat and 8.25% MSNF. This is the recommended standard.

In the recent past, major advances in dairy processing have resulted in improvement in safety and quality of products. In particular, ultra-pasteurization techniques and aseptic packaging systems have presented the industrial user with extended and long shelf-life products.

Basic Steps in Milk Processing

It is beneficial for food developers and processors to know the basic steps involved in dairy processing. A detailed description of basic dairy processing is given in Chapter 4. Milk production, transportation, and processing are regulated by Grade A Pasteurized Milk Ordinance (USDHHS PMO, 2003; Frye and Kilara, 2006). Chapter 15 of this book deals with the regulatory aspects of dairy-based ingredients. Figure 1.3 shows the journey of milk from the farm to supermarket, including processing at the milk plant.

Figure 1.3. The journey of milk from farm to market.

Bulk Milk Handling and Storage

The handling and storage of bulk milk are key components of good quality milk. Dairy farms produce sanitary raw milk under the supervision of U.S. Public Health Services (Pasteurized Milk Ordinance). The regulations help in the movement of assured quality milk across interstate lines.

Today, virtually all the raw milk at the plant is delivered in tank trucks. Unloading of milk involves agitation of the truck, inspection for the presence of off-flavors, collection of a representative sample, and connection of the unloading hose to the truck outlet. After opening the tank valve, a high-capacity transfer pump is used to pump milk to a storage tank or silo. The weight of milk transferred is registered with a meter or load cells. The tank truck is then cleaned by plant personnel by rinsing with water, cleaning with detergent solution, rinsing again with water, and finishing with a chlorine/iodine sanitizing treatment. A clean-in-place line may be inserted into the tank through the manhole. Payment of milk is based on the hauler receipt.

Storage tanks may be refrigerated or insulated. They hold milk up to 72 hours (usually 24 hours) before processing. The tanks may be horizontal or vertical in configuration. Grade A milk for pasteurization must be stored at 1.7°C to 4.4°C (35°F to 40°F). The maximum bacterial count at this stage is 300,000 CFU/ml, as opposed to the maximum of 100,000 CFU/ml allowed at the farm. The higher count is justified because pumping breaks the clumps of bacteria, which gives higher counts and provides more opportunity for contamination of milk as it comes in contact with more equipment during handling and transfer. Also, the longer storage time adds more bacterial numbers. The 3-A sanitary standards are followed for equipment design (Frye, 2006). Chapter 3 deals with the microbiological aspects of milk and dairy ingredients.

Separation

The purpose of the separation step is to separate milk into cream and skim milk. All incoming raw milk is passed through the separator, which is essentially a high-speed centrifuge. This equipment separates milk into lighter cream fraction and heavier skim milk fraction. A separator of adequate bowl capacity collects all the “slime” material containing heavy casein particles, leukocytes, larger bacteria, body cells from cows’ udders, dust and dirt particles, and hair. Homogenized milk develops sediment upon storage if this particulate fraction of raw milk is not removed. Skim milk and cream are stored separately for further processing.

Standardization

Use of a separator also permits fractionation of whole milk into standardized milk (or skim milk or low-fat milk) and cream. Skim milk should normally contain 0.01% fat or less. A standardization valve on the separator permits the operator to obtain separated milk of a predetermined fat content. Increased back pressure on the cream discharge port increases the fat content in standardized milk. By blending cream and skim milk fractions, various fluid milk and cream products of required milk fat content can be produced.

Heat Treatment

The main purpose of heat treatment of milk is to kill 100% of the disease-producing (pathogenic) organisms and to enhance its shelf life by removing approximately 95% of all the contaminating organisms. Heat treatment is an integral part of all processes used in dairy manufacturing plants. Intensive heat treatment brings about interactions of certain amino acids with lactose, resulting in color changes in milk (Maillard browning) as observed in sterilized milk and evaporated milk products.

Among milk proteins, caseins are relatively stable to heat effects. Whey proteins tend to denature progressively by severity of heat treatment, reaching 100% denaturation at 100°C (212°F). In the presence of casein, denatured whey proteins complex with casein, and no precipitation is observed in milk. In contrast to milk, whey that lacks casein, and heat treatment at 75°C to 80°C (167°F to 176°F) results in precipitation of the whey proteins.

From a consumer standpoint, heat treatment of milk generates several sensory changes (cooked flavor) depending on the intensity of heat. In general, pasteurized milk possesses the most acceptable flavor. Ultra-pasteurized milk and ultra-high-temperature (UHT) milk exhibit a slightly cooked flavor. Sterilized milk and evaporated milk possess a pronounced cooked flavor and off-color.

The U.S. Food and Drug Administration (PMO) has defined pasteurization time and temperature for various products. The process is regulated to assure public health. Milk is pasteurized using plate heat exchangers with a regeneration system. The process of pasteurization involves heating every particle of milk or milk product in properly designed and operated equipment to a prescribed temperature and holding it continuously at or above that temperature for at least the corresponding specified time. Minimum time-temperature requirements for pasteurization are based on thermal death time studies on the most resistant pathogen that might be transmitted through milk. Table 1.3 gives the various time-temperature requirements for legal pasteurization of dairy products.

Table 1.3. Minimum time-temperature requirements for legal pasteurization in dairy operations.

Adapted from Chandan (1997), Partridge (2008), USHHS FDA (2003)

Most refrigerated cream products are now ultra-pasteurized by heating to 125°C to 137.8°C (257°F to 280°F) for two to five seconds and packaged in sterilized cartons in clean atmosphere. For ambient storage, milk is UHT treated at 135°C to 148.9°C (275°F to 300°F) for four to 15 seconds, followed by aseptic packaging. In some countries, sterilized/canned milk is produced by a sterilizing treatment of 115.6°C (240°F) for 20 minute. It has a light brown color and a pronounced caramelized flavor.

Homogenization

Homogenization reduces the size of fat globules of milk by pumping milk at high pressure through a small orifice, called a valve. The device for size reduction, the homogenizer, subjects fat particles to a combination of turbulence and cavitation. Homogenization is carried out at temperatures higher than 37°C (99°F). The process causes splitting of original fat globules (average diameter approximately 3.5 µm) into a very large number of much smaller fat globules (average size less than 1 µm). As a consequence, a significant increase in surface area is generated. The surface of the newly generated fat globules is then covered by a new membrane formed from milk proteins. Thus, the presence of a minimum value of 0.2 g of casein/g fat is desirable to coat the newly generated surface area. As milk is pumped under high pressure conditions, the pressure drops, causing breakup of fat particles.

If the pressure drop is engineered over a single valve, the homogenizer is deemed to be a single-stage homogenizer. It works well with low-fat products or in products in which high viscosity is desired, as in cream and sour cream manufacture. On the other hand, homogenizers that reduce fat globule size in two stages are called dual-stage homogenizers. In the first stage the product is subjected to high pressure (for example, 13.8 Mpa, 2,000 psi) which results in breakdown of the particle size diameter to an average of less than 1 µm. Then the product goes through the second stage of 3.5 MPa (500 psi) to break the clusters of globules formed in the first stage. Dual stage homogenization is appropriate for fluids with high fat and solids-not-fat content or whenever low viscosity is needed.

Homogenized milk does not form a cream layer (creaming) on storage. It displays a whiter color and fuller body and flavor characteristics. Homogenization leads to better viscosity and stability by fully dispersing stabilizers and other ingredients in ice cream, cultured products, and other formulated dairy products.

Cooling, Packaging, and Storage

Pasteurized fluid milk products are rapidly cooled to less than 4.4°C (40°F), packaged in appropriate plastic bottles/paper cartons, and stored in cold refrigerated rooms for delivery to grocery stores or warehouses for distribution.

Fluid Milk Products

Commercial milk is available in various milk fat contents. The approximate composition of fluid milk products is shown in Table 1.4. The term “milk” is synonymous with whole milk, which must contain not less than 3.25% milk fat and 8.25% solids-not-fat. Addition of vitamins A and D is optional. If the vitamins are added, vitamin A must be present at a level of not less than 2,000 IU/quart and vitamin D must be present at 400 IU/quart.

Table 1.4. Typical composition of fluid dairy ingredients.

*UF, ultra-filtered

Adapted from Chandan (1997), Chandan and O’Rell (2006a)

Fat-reduced milks are labeled according to their contribution of grams of fat per reference amount (RA) of 240 ml. Low-fat milk contributes less than 3 g fat per RA, whereas nonfat milk contributes less than 0.5 g of fat per RA. Because 2% milk contributes 4.8 g fat/RA, it is labeled reduced-fat milk. For a detailed discussion of fluid milk products, see Partridge (2008).

Figure 1.4 shows the steps in production of fluid milk and cream products. The figure shows general processes for manufacture of whole milk, reduced-fat milk, low-fat milk, and skim milk. It also shows how cream and other fluid products are made.

Figure 1.4. Processes for fluid milk and cream.

The shelf life of milk is a function of the microbial quality of raw milk, temperature, and time of exposure during storage and handling, pasteurization conditions, equipment sanitation, packaging conditions, and subsequent distribution practices. Fluid milk products display maximum keeping quality when stored at temperatures close to the freezing point (4°C/39.2°F). Let us assume the shelf life of pasteurized milk is 40 days at the storage temperature of 0°C (32°F). It has been demonstrated that the shelf life is shortened to 20 days by storage at 2°C (35.6°F), 10 days at 4°C (39.2°F), 5 days at 7°C (44.6°F), and progressively to fewer days at higher temperatures. This illustration underscores the importance of maintaining refrigerated storage temperature as low as possible to achieve the maximum shelf life of milk.

Ultra-pasteurized products are packaged in a near-aseptic atmosphere in pre-sterilized containers and held refrigerated to achieve an extended shelf life. When an ultra-pasteurized product is packaged aseptically in a specially designed multilayer container, it displays a shelf life longer than any other packaged fluid milk and cream products. UHT products subjected to aseptic heat treatment and packaged aseptically in specially designed multilayer containers can be stored at ambient temperatures for several months.

Fluid Cream

Cream is prepared from milk by centrifugal separation. Heavy cream contains not less than 36% fat and may be called heavy whipping cream. Light whipping cream contains 30% or more milk fat, but less than 36% milk fat and may be labeled as whipping cream. Light cream, coffee cream, or table cream contains not less than 18% milk fat, but less than 30% milk fat. Half and half is normally a blend of equal proportion of milk and cream, containing 10.5% milk fat. Legally, it contains not less than 10.5% milk fat but not more than 18% milk fat. Cream to be used as an ingredient in processing contains 36% to 40% fat. Cream of different fat levels can be produced by standardizing with skim milk. Light cream and half and half are homogenized products. Specific homogenization and heat treatments generate desirable grades of viscosity in cream products. They are processed and packaged similar to fluid milks.

Plastic cream contains 80% milk fat. It resembles butter in consistency but compared to butter, it is still oil-in-water type emulsion. As an ingredient, it can be stored in frozen form.

Fat-rich Products

Butter

The manufacture of butter and spreads is discussed in another publication (Fearon and Golding, 2008) and in Chapter 9 of this book. Butter is a concentrated form of milk fat, containing at least 80% fat. It can be converted to shelf-stable products such as butter oil, anhydrous milk fat, and ghee. Table 1.5 shows the approximate composition of butter and its products.

Table 1.5. Typical composition of milk fat concentrates.

Adapted from Chandan (1997), Aneja et al. (2002)

Figure 1.5 is flow-sheet diagram for the manufacture of butter, butter oil, and certain dry milk products. The diagram also displays interrelationships between these products. Butter is obtained by churning cream. The temperature of churning is an important parameter to follow. The churning temperature is determined by an optimum ratio of crystalline fat, solid fat, and liquid fat. The churns are either batch type or continuous type. For batch-type churns, cream of 35% to 45% fat is used. For continuous type churns, cream of 42% to 44% fat is used. Cream is pasteurized at 73.8°C (165°F) for 30 minutes or at 85°C (185°F) for 15 seconds and is then cooled to about 7°C (45°F) for crystallization of fat. The crystallization process is completed by holding the cream for approximately 16 hours.

Figure 1.5. Flow sheet diagram for butter, butter oil, dry buttermilk, nonfat dry milk, and dry whole milk.

The cream that registers an increase in temperature to 10°C (50°F) is then transferred to a sanitized churn. Annatto coloring may be incorporated, if required. The churn is continuously rotated to convert oil-in-water type of emulsion (cream) to water-in-oil type emulsion (butter). This conversion is known as phase inversion. This is accompanied by the appearance of butter granules of the size of popcorn or peas. Cream begins to foam during phase inversion. Free fat generated by rupture of fat globules of cream cements some of the remaining fat globules to form clumps or butter granules. There is a clear separation of butter granules from the surrounding liquid, called buttermilk. At this stage, the buttermilk is drained out, followed by the addition of an aliquot of clean cold water (1°C to 2°C/33.8°F to 35.6°F) to the churn. The total volume of wash water is equal to the volume of buttermilk. The washing continues until the rinse is almost clear. Salt at 1.6% level is added and blended with butter. The next step is called “working,” in which the remaining fat globules are disrupted to liberate free fat.

All of the free fat then forms the continuous phases in which water droplets are dispersed to form butter. Working of butter is accomplished by continuous rotation of the churn until the body of butter is closely knit to show a waxy character with no visible pockets of surface moisture. The working of butter is continued to standardize moisture until the fat content of butter is 80%. Butter is then pumped and packaged.

Continuous butter churns are now widely in use. They accelerate the churning process, and washing of butter is not necessary. Cream of 42% to 44% fat is introduced into a cylinder, where it is churned. Buttermilk is drained and butter granules are worked to obtain the typical waxy body and texture of butter, followed by packaging. In another process, cream is separated to get plastic cream of 80% fat. The phase inversion is carried out by chilling. The butter granules are worked to achieve typical butter body and texture.

In some countries, butter is churned from cultured cream. Cultured cream butter has a distinct flavor and can be easily distinguished from sweet cream butter.

The processing conditions affect the physical properties such as crystallization and melting behavior of butterfat. The crystal formation is mediated by nucleus formation and subsequent growth of crystals. The size of crystals depends on rate of crystallization. Melting behavior influences the application of butter in food products. The rate of transformation of solid fat fraction into liquid milk fat is important and is characterized by melting point range, thermal profile, and solid fat content. The melting point temperature is the temperature at which milk fat melts completely to a clear liquid. It occurs at a range of 32°C to 36°C (90°F to 97°F) and assumes completely liquid state at 40°C (104°F). It acquires completely solid state at −75°C (−103°F). At ambient temperature, it is a mixture of crystals and liquid phases.

By manipulating temperature, butterfat has been fractionated into three fractions exhibiting distinct functionalities. Low-melting fraction melts below 10°C (50°F), middle-melting fraction melts between 10°C and 20°C (50°F and 68°F), and high-melting fraction melts above 20°C (68°F). Low-melt fraction contains significantly lower levels of saturated fatty acids. Butter made with very low-melt fraction spreads at refrigerated temperature. Further fractionation leads to very high-melting fraction that melts at a temperature higher than 50°C (above 122°F), behaving like cocoa butter in confectionery products.

Light/reduced fat butter contains 40% fat. The reduced fat form cannot be used for baking.

Butter-vegetable oil blends are obtained by blending certain vegetable oils such as corn oil or canola oil emulsified into cream prior to the churning process. The objective is to reduce the saturated fatty acid content to enhance the healthy perception of the product or to make the product easily spreadable at refrigeration temperature.

Butter oil is at least 99.6% fat and contains less than 0.3% moisture, and traces of milk solids-not-fat. Butter is melted by heating gently to break the emulsion and centrifuged in a special separator to collect milk fat, followed by vacuum drying.

Anhydrous milk fat or anhydrous butter oil is obtained from plastic cream of 70% to 80% fat. Phase inversion takes place in a special unit (separator) and the moisture is removed by vacuum drying. It contains at least 99.8% milk fat and no more than 0.1% moisture.

Ghee is another concentrated milk fat that is widely used in tropical regions of the world, especially in South Asian countries. It is a clarified butterfat obtained by desiccation of butter at 105°C to 110°C (221°F to 230°F). The intense heat treatment generates a characteristic aroma and flavor brought about by heat-induced interactions of components of milk solids of butter. The detailed manufacturing procedure for ghee is given elsewhere (Aneja et al., 2002).

Concentrated/Condensed Fluid Milk Products

For a detailed description of condensed milk and dry milks, see the publications of Farkye (2008) and Augustin and Clarke (2008), and Chapters 5 and 6 of this book. An outline for manufacturing dry whole milk, nonfat dry milk, and dry buttermilk powder is depicted in Figure 1.5. The functional properties of concentrated milk products including nonfat dry milk can be manipulated by specific heat treatment. It also affects the keeping quality of whole milk powder. The temperature and time combinations can vary widely depending on the required functional properties. Invariably, the milk for manufacture of concentrated milk products is pasteurized (high-temperature, short-time) by heating to at least 72°C (161°F) and holding at or above this temperature for at least 15 seconds. An equivalent temperature-time combination can be used. With condensed milk and nonfat dry milk, the extent of heat treatment can be measured by the whey protein nitrogen index, which measures the amount of undenatured whey protein.

Removal of a significant portion of water from milk yields a series of dairy ingredients. Consequently, these ingredients offer tangible savings in costs associated with storage capacity, handling, packaging, and transportation. The composition of concentrated milk products is shown in Table 1.6.

Table 1.6. Typical composition of condensed milk products.

Adapted from Chandan (1997)

Concentrated milk or condensed whole milk is obtained by removing water from milk and contains at least 7.5% milk fat and 25.5% milk solids. Condensed milk is available in whole milk, low-fat, and nonfat varieties. Condensed whole milk is purchased largely by confectionary industries. It is pasteurized but not sterilized by heat. It may be homogenized and supplemented with vitamin D.

Condensed skim milk is commonly used as a source of milk solids in dairy applications and in the manufacture of ice cream, frozen yogurt, and other frozen desserts. Condensed milks are generally customized orders. User plants specify total solids concentration, fat level, heat treatment, and processing conditions. The dairy concentrates offer economies of transportation costs and storage space. They must be transported and stored at 4.4°C (40°F), and to preserve quality they are used within five days.

Depending on the end user requirements, raw milk is standardized to desired milk fat : nonfat solids ratio. In general, the original milk volume is reduced to about one-third to yield about 25% to 40% solids in the final product. The standardized milk is preheated to 93.3°C (200°F) and held for 10 to 20 minutes. The objective of preheat treatment is to destroy microorganisms and enzymes and to increase heat stability of the milk. In addition, the viscosity of condensed milk is controlled by a time-temperature regime during preheat treatment. The heated milk is concentrated in energy-efficient multi-effect evaporators that operate in high vacuum condition to boil off water at moderate temperatures of 46.1°C to 54.4°C (115°F to 130°F). The concentrated milk is continuously separated from water vapor to achieve desirable concentration of milk solids. It may be homogenized prior to cooling and packaging or pumped to insulated trucks for transportation to user plants.

Sweetened condensed milk contains 60% sugar in the water phase, which imparts a preservative effect. Consequently, it has enhanced shelf life. When packaged properly, the product is stable for many months at ambient storage temperature. Because it does not need high heat treatment for sterilization, it possesses a much better color and flavor than evaporated milk. Condensed milk may be low fat and nonfat. It is derived from milk after the removal of 60% of its water. It must contain at least 8% milk fat and 28% milk solids. The viscosity of the product is high, approximating 1,000 times that of milk. Sweetened condensed milk is used in confectionery manufacture as well in the manufacture of exotic pies and desserts.

Manufacture of sweetened condensed milk resembles the manufacture of condensed skim milk given above. The addition of sugar and control of lactose crystal size require special processing procedures. The standardized milk is preheated at 135°C (275°F) for 5 seconds or 110°C to 120°C (230°F to 248vF) for 10 to 20 seconds. The ultra-heat treatment is preferred over high-temperature-short-time treatment because it leads to lower viscosity in sweetened condensed milk. Following homogenization at 70°C (158°F) at 3.5 MPa (500 psi), milk is concentrated in an efficient evaporator at 82.2°C (180°F) and liquid sucrose is blended. At this stage, the mix is standardized to 8.5% fat, 20% nonfat solids, and 44% sucrose. The blend is then pasteurized at 82.2°C (180°F) for 30 seconds and further standardized to desirable solids in the finishing pan. The product is cooled to 60°C (140°F), followed by seeding with finely ground lactose at the rate of 0.03% (dry matter basis). At this stage the mixture is agitated vigorously while cooling to 18.3°C (65°F).

The lactose crystal size must be less than 10 µm to avoid settling in storage and to prevent sandiness in the product. Sweetened condensed milk is packaged in metal or plastic containers and sealed. For bulk sales, it is pumped into insulated trucks for transport and delivery to user plants.

Evaporated milk is also concentrated milk that is homogenized and heat sterilized in sealed cans or bottles. It is made by boiling off 60% of the water content of milk. It must contain at least 6.5% milk fat and 23% milk solids. Evaporated milk is heat-sterilized. The sterilization process renders the product safe for consumption and it can be stored at room temperature for several months without deterioration of flavor. The current processing trend is to subject the product to ultra-heat treatment, followed by aseptic packaging. This process gives a product with better color and flavor than the in-can sterilized product. Typically, the concentration factor is of the order of 2.1 times, giving a milk fat level of approximately 8% and nonfat solids of approximately 18%. Low-fat evaporated milk composition is 4% fat and 20% nonfat solids, whereas nonfat evaporated milk contains 0.1% fat and 22% nonfat solids. Evaporated milk is mainly a retail canned product used by the consumer as a convenience ingredient in the preparation of meals, snacks, and desserts.

Manufacture of evaporated milk involves standardization of milk to a desired fat : nonfat solids ratio and preheating to 135°C (275°F) for 30 seconds. The milk is concentrated in a vacuum evaporator at 68.3°C to 82.2°C (155°F to 180°F) and homogenized at 65°C (14°F) and 20.7 MPa (3,000 psi), first stage, and 3.5 MPa (500 psi), second stage. It is then cooled to 10°C (50°F) and stabilized with disodium hydrogen phosphate to reduce age thickening during subsequent storage. The product is packaged in metal cans and sealed, followed by sterilization at 120°C (248°F) for 15 minutes.

In a more recent process, the product is vacuum-concentrated and stabilized with disodium hydrogen phosphate as in the conventional process. It is then sterilized at 140.6°C (285°F) for 15 seconds, cooled to 60°C (140°F), and homogenized at 41.3 MPa (6,000 psi). After cooling to 10°C (50°F), evaporated milk is packaged aseptically in appropriate containers.

Dry Milk Products

Table 1.7 gives the typical composition of dry milk products.

Table 1.7. Typical composition of dry milk products.

Adapted from Chandan (1997), Chandan and O’Rell (2006a)

Nonfat dry milk (NFDM) is the product resulting from the removal of fat and water from milk. It contains the lactose, milk proteins, and milk minerals in the same relative proportions as in the fresh milk from which it was made. It contains no more than 5% moisture by weight. The fat content does not exceed 1.5% by weight unless otherwise indicated. NFDM is used in dairy products, bakery goods, dry mixes, chemicals, and meat processing, and in homes for cooking.

NFDM is manufactured by spray drying condensed skim milk. Spray drying involves atomizing concentrated milk into a hot air stream 180°C to 200°C (356°F to 392°F). The atomizer may be a pressure nozzle or a centrifugal disc. By controlling the size of the droplets, the air temperature, and the airflow, it is possible to evaporate almost all the moisture while exposing the solids to relatively low temperatures. Spray drying yields concentrated and dry milk ingredients with excellent solubility, flavor, and color.

The spray drying process is typically a two-stage process that involves the spray dryer at the first stage with a static fluid bed integrated in the base of the drying chamber. The second stage is an external vibrating fluid bed. The product is moved through the two-stage process quickly to prevent overheating of the powder. The powder leaves the dryer and enters a system of cyclones that simultaneously cools it.

Roller drying is another process but is no longer widely used in the manufacture of most dry milk products. This process involves direct contact of a layer of concentrated milk with the hot surface of rotating rollers. It causes adverse effects of excessive heat on milk components. In this process, heat often causes irreversible changes such as lactose caramelization, Maillard reaction, and pro­tein denaturation. Roller drying typically results in more scorched powder particles and poorer powder solubility than spray drying. However, roller dried milk absorbs more moisture than spray dried powder and is preferred in some food applications such as bakery products.

Instant NFDM is a processed NFDM to improve its dispersion properties. It reconstitutes readily in cold water. The instantizing process involves agglomeration, a process of increasing the amount of air incorporated between powder particles. In one process, a small amount of moisture is incorporated in dry milk particles suspended in air, forming porous aggregates, followed by re-drying and grinding the agglomerated particles. The process results in dry milk with improved reconstitution properties. During reconstitution, the air is replaced by water and incorporated air enables a larger amount of water to come into contact immediately with the powder particles.

Dry whole milk is the product resulting from the removal of water from milk, and it contains not less than 26% nor more than 40% milk fat and not more than 5% moisture (as determined by weight of moisture on a milk solids-not-fat basis). It is manufactured by spray drying whole milk with an added wetting agent, soy lecithin. Reconstituted extra grade whole milk powder possesses a sweet, pleasant flavor. It may have a slight degree of feed flavor, a definite degree of cooked flavor, and no off-flavors. The product should be free of graininess on reconstitution and exhibit no burnt particles. Dry whole milk is used primarily in confectionary, dairy and bakery products.

Dry buttermilk