Ultra-high temperature processing (UHT), ultra-heat treatment, or ultra-pasteurization is a food processing technology that sterilizes liquid food by heating it above 140 °C (284 °F) – the temperature required to kill bacterial endospores – for two to five seconds. UHT is most commonly used in milk production, but the process is also used for fruit juices, cream, soy milk, yogurt, wine, soups, honey, and stews. UHT milk was first developed in the 1960s and became generally available for consumption in the 1970s. The heat used during the UHT process can cause Maillard browning and change the taste and smell of dairy products. An alternative process is flash pasteurization, in which the milk is heated to 72 °C (162 °F) for at least fifteen seconds.

UHT milk packaged in a sterile container has a typical unrefrigerated shelf life of six to nine months. In contrast, flash-pasteurized milk has a shelf life of about two weeks from processing, or about one week from being put on sale.

The most commonly applied technique to provide a safe and shelf-stable milk is heat treatment. The first system involving indirect heating with continuous flow (125 °C [257 °F] for 6 min) was manufactured in 1893. In 1912, a continuous-flow, direct-heating method of mixing steam with milk at temperatures of 130 to 140 °C (266 to 284 °F; 403 to 413 K) was patented. However, without commercially available aseptic packaging systems to pack and store the product, such technology was not very useful in itself, and further development was stalled until the 1950s. In 1953, APV pioneered a steam injection technology, involving direct injection of steam through a specially designed nozzle which raises the product temperature instantly, under brand name Uperiser; milk was packaged in sterile cans. In the 1960s, APV launched the first commercial steam infusion system under the Palarisator brand name.

In 1952, in Sweden, Tetra Pak launched tetrahedral paperboard cartons. They made a commercial breakthrough in the 1960s, after technological advances, combining carton assembling and aseptic packaging technologies, followed by international expansion. In aseptic processing, the product and the package are sterilized separately and then combined and sealed in a sterile atmosphere, in contrast to canning, where product and package are first combined and then sterilized.

In 1983, the UK Parliament passed the Importation of Milk Act 1983, following a successful appeal to the European Court of Justice that prevented the government from banning the importation of UHT milk.

In June 1993, Parmalat introduced its UHT milk to the United States. In the American market, consumers are uneasy about consuming milk that is not delivered under refrigeration, making them reluctant to buy it. To combat this, Parmalat is selling its UHT milk in old-fashioned containers, unnecessarily sold from the refrigerator aisle. UHT milk is also used for many dairy products.^{[citation needed]}

In 2008, the UK government proposed to produce nine units out of every ten as UHT by 2020, which they believed would significantly cut the need for refrigeration, and thus benefit the environment by reducing greenhouse gas emissions. The milk industry opposed this, however, and the proposition was abandoned.^{[citation needed]}

Ultra-high-temperature processing is performed in complex production plants, which perform several stages of food processing and packaging automatically and in succession: