1. High temperature methods
Pasteurisation and UHT
During pasteurisation liquid is heated and held at a high temperature for a short time.
Pasteurisation is mainly used to process milk, fruit juices and other liquids.
Different liquids are heated to different temperatures for different amounts of time.
Milk is usually heated to 72C for 15 seconds and then cooled rapidly to below 10C which extends the shelf life by days. But only kills some bacteria.
During UHT liquid is heated to a very high temperature for a short time . Milk is heated to 133C for 1 second and this extends the shelf life by months. There is no change to the flavour and kills of all the bacteria.

2. Sterilisation
During sterilisation food is heated to high temperatures for longer than pasteurisation or UHT.
When sterilising milk is heated to 110C and held for 30 minutes, which extends the shelf life by months. In milk the flavour is changed because of caramelisation of the milk sugar lactose. Most bacteria are destroyed.

3. Canning
Canning is a form of sterilisation. Food can be packed in cans or bottles and then sterilised.
Sterilised and then packed into sterile containers.
The advantages of canning are that food
Has a very long shelf life
Can be kept at ambient room temperature.
Once the can is opened it should be treated like fresh food.