🌡️ Pasteurization

Pasteurization is heating milk to kill harmful germs. The most common method is quick pasteurization: 72–75 °C for 15–20 seconds, then cooling straight away. There is also long pasteurization: 63 °C for 30 minutes. Pasteurized milk keeps in the fridge for about 7–10 days.

The heat destroys the germs that cause tuberculosis and brucellosis, as well as salmonella, listeria, campylobacter, the dangerous E. coli O157:H7 and others. But not all bacteria: the spores of many of them survive. So pasteurized milk still has to be kept cold. To check whether pasteurization worked, they test for an enzyme called alkaline phosphatase: if it is destroyed, the heating was enough. The food value hardly changes: of the vitamins, only vitamin C drops noticeably, and milk has little of it anyway.

Pasteurized or sterilized milk? Pasteurization is a gentle heating that leaves spores alive, so the milk needs the fridge; sterilization goes above 100 °C and gives months of shelf life with a “cooked” taste. Pasteurized or UHT? UHT heats milk to at least 135 °C for a few seconds and the pack in an aseptic seal stays stable at room temperature. Pasteurized or boiled? Boiling at home is usually unnecessary, since the harmful germs were already killed at the dairy. Pasteurized or raw? Only the heating step differs, and the FDA warns about the danger of raw milk.

On the pack, look for the word “pasteurised” (or “pasteurized”), a use-by date and the instruction to keep refrigerated. Milk marked “UHT” or “sterilised” is a different treatment and is sold on ordinary shelves. Pasteurized milk is sold chilled in supermarkets, convenience shops and at dairies. Cream, kefir, yogurt, curd cheese and many cheeses are made from pasteurized milk, so the same word can appear on those labels.

The method is named after Louis Pasteur. In 1865 he patented heating wine to stop it from spoiling. In 1886 the German chemist Franz von Soxhlet suggested pasteurizing the milk sold to the public. Later, pasteurizing milk became compulsory in many cities and countries. Pasteurized milk is used to make drinking milk, cream, kefir, yogurt, curd cheese and many cheeses.