The ultra-high temperature (UHT) process consists of the sterilisation of food before packaging, after which the product is filled into pre-sterilised containers in a sterile atmosphere. The high temperatures involved in such a process can reach values as high as 137-140°C for a few seconds in order to eliminate all microorganisms. Milk can be made commercially sterile by subjecting it to temperatures in excess of 100° C, and packaging it in airtight containers. The milk may be packaged either before or after sterilization.

This technique is not only applied to milk; it can be applied to several products including juices, cream, yoghurt, wine, salad dressings, baby foods, tomato products and soups and stews. Therefore, if the label of a dairy product characterises it as UHT, it might mean that this process has been used to treat not only the milk, but also the whole product.