🌡️ Pasteurization

Pasteurization is heating milk to kill harmful germs. The most common method is quick pasteurization: 72–76 °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 5–10 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; only the amount of vitamins B1, B12 and C drops a little.

The method is named after Louis Pasteur. In the 1860s he heated young wine to 50–60 °C to stop it from spoiling. In 1886 the German chemist Franz von Soxhlet suggested treating milk the same way, and in the 1880s the first industrial pasteurizers were made in Germany. 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.