UHT

Ultra-high temperature processing (UHT), ultra-heat treatment, or ultra-pasteurization is a food processing technology that sterilizes liquid food, chiefly milk, by heating it above 135 °C (275 °F) – the temperature required to kill spores in milk – for 1 to 2 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 HTST pasteurization (high temperature/short time), in which the milk is heated to 72 °C (162 °F) for at least 15 seconds.

UHT milk packaged in a sterile container, if not opened, has a typical unrefrigerated shelf life of six to nine months. In contrast, HTST 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 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 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 Sweden, Tetra Pak launched tetrahedral paperboard cartons in 1952. 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.

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