Dairy Processing (Food Cycle Technology Source Book)

Excerpt. © Reprinted by permission. All rights reserved. Dairy Processing Food Cycle Technology Source Books By UNIFEM Practical Action Publishing LtdCopyright © 1996 The United Nations Development Fund for Women (UNIFEM) All rights reserved. ISBN: 978-1-85339-335-8 Contents PREFACE, vii, ACKNOWLEDGEMENTS, viii, INTRODUCTION, 1, 1 Milk processing, 3, 2 Traditional methods and products, 9, 3 Improving milk processing technologies, 26, 4 Socio-economic considerations, 42, 5 Case studies, 49, GLOSSARY OF TERMS, 58, EQUIPMENT SUPPLIERS, 59, INSTITUTIONS, 60, REFERENCES AND FURTHER READING, 62, CHAPTER 1 Milk processing The perishable nature of milk means that some form of processing is necessary to extend its shelf-life, transform it into different products to expand its market and to generate income by adding value. Ordinary heat treatment or pasteurization, while destroying harmful bacteria, does not make milk absolutely free from spoilage organisms. In a tropical climate, milk becomes unfit for human consumption within a day or two. Processing milk into dairy products makes it more stable for storage over extended periods of time. In the tropics where ambient temperatures are high and refrigeration is not readily available, milk may be concentrated by boiling or made into butter, ghee or other products which keep better at room temperatures. When there is an abundant local supply, storage and marketing may have a low priority, leading to wastage. Processing helps eliminate wastage and also adds value. In many tropical areas, there is a cultural reluctance to use fresh milk, which probably derives from safety considerations. In Africa and Asia, lactose intolerance (an inability to digest milk sugar) is common. The consumption of fermented cheeses and yoghurts, in which the lactose has been converted into lactic acid, has helped reduce the problem. The limited market for liquid milk is a problem which can thus be remedied by creating a demand for processed milk products. Through community milk centres, such processing can create jobs, while at the home level it provides added income for the family. General methods of milk processing While there are numerous ways of processing milk that vary in detail, they can be classified into three broad areas. These areas may overlap and a combination of the two main methods may be used to make a better preserved product. The first general method involves increasing the acidity (or lowering the milk pH). This slows down, or may prevent, the growth of spoilage micro-organisms and the action of enzymes (natural substances that cause changes in flavour, etc.). Increasing the milk's acidity can be achieved by: * lactic acid fermentation: beneficial micro-organisms ferment the milk sugar, turning lactose to lactic acid. * the addition of organic acids: for example, vinegar or lime juice. The second method involves lowering the moisture content to a level which is sufficiently low to control the growth of microorganisms and the action of enzymes, so making the product more stable. Moisture content can be lowered by: * evaporation of water using heat; * curdling the milk and removing the whey, or watery part, as in the case of cheese; * mechanical separation of the fat by churning, in the making of butter; * adding salt and sugar to bind part of the water as in the salting of cheese or making milk sweets; * sun or air drying of products such as cheeses or milk casein, the milk protein; * mechanical drying, for example roller and spray-dried milk powders. The third method simply involves heating to produce either pasteurized or sterilized milk. Milk composition Milk contains the essential nutrients in the right proportions necessary to support a young mammal in the first stages of its life. It is a good source of carbohydrate, fat and protein as well as many vitamins and minerals. The composition of milk varies from one species to another. In most countries, the principal source of milk is