12.4.4 Methods of making milk safe
Remember that raw milk should not be consumed without treatment to protect consumers from milkborne diseases. The following methods are recommended:
This is the most widely practised domestic method of making milk safe. Milk must be boiled for 30 minutes and then cooled to below 10ºC. It must be protected from contamination by flies, dust, etc. Boiling in this way can prevent the transmission of bovine TB and brucellosis.
This method ensures that all microorganisms and their spores are killed, but it also affects the nutritional quality of the milk as the process destroys vitamins, especially vitamin C. Sterilisation is carried out by raising the temperature to between 110ºC and 130ºC for at least 20 minutes.
In the drying process all the water is removed by evaporation and what remains is solid, dry milk (powdered milk). The powder is not sterile, but once dry, it can be stored for extended periods.
Why does drying make it safe to store powdered milk?
Bacteria and other microorganisms need water to survive. Drying prevents the growth and reproduction of microorganisms that could contaminate the milk. But it must also be stored correctly. It must be kept in an air-tight container to ensure it remains dry and free from dust and dirt.
What is pasteurisation?
Pasteurisation is a process of heat treatment of food that kills most pathogenic micoorganisms without altering the nutritional value.
Pasteurisation is not sterilisation but it is a process in which all pathogenic microorganisms, many other non-spore forming bacteria and many enzymes in the milk are destroyed or inactivated without much affecting the nutritive value and the chemical nature of the milk. In practice one expects to find no faeco-oral bacteria and not more than 10,000 microorganisms of any type per millilitre of pasteurised milk. You learned the details of pasteurisation in Study Session 10.