🌡️ UHT processing

UHT processing (ultra-high temperature) is very strong and very short heating: 135–150 °C for a few seconds. In practice it is most often 137–142 °C for 4–6 seconds. The milk is first warmed to 70–80 °C, then instantly brought to the right temperature and cooled straight away. This heating kills not only microbes but also their spores.

There are two ways to heat it. In direct heating, clean steam is fed into the milk, and the extra water is then removed in a vacuum chamber. In indirect heating, the milk is heated through the steel wall of a heat exchanger. Then the milk is filled aseptically: a sterile product into sterile packaging, in a sterile environment. An unopened carton keeps without a fridge for up to 6 months, sometimes longer.

The technology was developed from the late 19th century, but it became widespread in the 1960s–1970s, together with aseptic packaging. This milk tastes a little “cooked”, but milder than sterilised milk. In nutrition it is close to pasteurised milk. Countries drink it very differently: in 2007, it made up more than 95% of drinking milk in Belgium, Spain and France, but about 2% or less in Denmark, Greece and Ireland.