How is milk pasteurised and why is it necessary? [3 MARKS]

Reason out:1.5 Marks
Explanation: 1.5 Marks

In pasteurisation, milk is first heated to about 70 degree Celsius for 15 to 30 seconds. Then, it is suddenly chilled and stored. This prevents the growth of microbes. Pasteurisation deactivates the microbes and reduces the enzyme activity by reduction of temperature.
Making the milk go through a huge variation in temperature in a short time helps to prevent the growth of dangerous bacteria such as Salmonella, E.coli, Listeria. These are responsible for causing numerous foodborne illnesses.

Pasteurisation is necessary to increase the shelf life of milk and keep it microbe-free. It is one of the most important food-preservation method.