Dairy industries Milk. Milk is a food containing • • • • •
Sugar Fats Proteins Vitamins Minerals (such as calcium)
Milk is processed to: • •
Make it last longer Kill germs that might cause disease
Milk processes are: •
• • •
•
Evaporated milk o Much of the water in the milk is evaporated out o The heat treated milk is put in an evaporator, where it is concentrated Skimmed milk o The fat is taken out of the milk Semi-skimmed milk o Most of the fat is taken out of the milk but some is left Pasteurised milk o the milk is heated to 72ºC for 15 seconds then cooled rapidly to under 5ºC o Pasteurisation destroys most disease-causing microbes. o This milk will keep for 5 days in a fridge UHT milk. o This milk is heated to over 135ºC for 2-5 seconds. o This changes the taste of the milk o UHT treatment preserves milk and prolongs shelf life by destroying the microbes which cause milk to sour. o
It will keep at room temperature in a sealed container for a long time
Tests are carried out on milk for bacteria (germs) to test for fitness to drink. o o o o
The resazurin test is used to demonstrate the presence of bacteria. Blue resazurin is added to the milk The milk is heated to 40ºC for 20 minutes If the resazurin turns pink the milk is unfit to drink
Yoghurt. • Bacterial cultures can be added to pasteurised milk to make yoghurt. o o
Making yoghurt is a method of preserving milk. Bacterial cultures are added to the milk.