UHT (Ultra-high temperature) and HTST (High Temperature Short Time) are two pasteurization methods. The main difference between UHT and HTST milks is the intensity of the heat treatment which influences the shelf life of dairy products.
What is meant by shelf life? Shelf life refers to the period that milk can be stored before it starts to spoil. It is influenced by several factors such as the manufacturing processes, the way the product is packaged, storage conditions and whether the product has been opened, etc.
UHT is a processing technique used to make dairy products stay fresher, longer. UHT means that the milk is heated to about 140°C (284 °F) for around 4 seconds. This method eliminates essentially all the bacteria in milk. The average shelf life of UHT milk is 40-65 days if unopened and refrigerated appropriately. After opening, UHT milk should be kept refrigerated between 1°C to 4°C (33.8°F-39.2°F) and consumed within 7-10 days.
On the other hand, dairy products pasteurized using the HTST method are heated to about 72 °C (161.6 °F) for around 15 seconds to remove certain bacteria. Unopened HTST pasteurized milk products have a shelf life of 12–22 days. Once opened, HTST milk should be kept refrigerated between 1°C to 4°C (33.8°F-39.2°F) and consumed within 7-10 days.