
There are five main ways to preserve foods and remove microorganisms:
Chemicals
Drying
Refrigeration
Canning
Radiation
The History of HTST

There are various methods of pasteurization. In early 1900’s a batch method as used where a tank of milk was held at 145 degrees for 30 minutes. Pasteurization did not sterilize the milk and it still needed to be refrigerated afterwards. It did greatly reduce the number of bacteria in the milk so the chance of bacterial illness was minimized and the shelf life of the milk was increased. High Temperature Short Time continuous processes were developed between 1920 and 1927 and for some time the ability of the HTST process to produce safe milk was questioned.
There is also a UHT (ultra High temperature) method where the milk is heated well above boiling under pressure for just a few second. This product is essentially sterile and does not have to be refrigerated until it is opened. For most continuous processing, a high temperature short time pasteurizer is used. The heat treatment is accomplished using a plate heat exchanger. High Temperature Short Time Process