How does pasteurization kill bacteria on milk

  pasteurization [pastøriˈziːrʊŋ] or Pasteurization refers to the brief heating of substances to 60 to 90 ° C to kill microorganisms.

The process was named after the French chemist Louis Pasteur. He had recognized that brief heating of food and other substances kills most of the microorganisms contained in them. If the said substances are in a closed area, no new microorganisms can penetrate into them. This method was demonstrated very impressively with the help of the Pasteur flask. In the case of food, this can significantly increase the shelf life of food today. At the same time, spontaneous generation was refuted with this attempt.

Due to the short duration of the heat and the moderate temperature, most food spoilers such as lactic acid bacteria and yeast as well as many pathogenic bacteria such as salmonella are reliably killed without significantly changing the taste and consistency of the food. Durable bacterial spores like those of Clostridium botulinum, the pathogens of paratuberculosis and mold spores survive this treatment at least partially. For this reason, the germ load of the raw material should be kept as low as possible.



Pasteur's proof that food spoilage is clearly caused by living beings and is not a purely chemical process, as many of his contemporaries assumed, can serve as a preliminary test for developing the process. To prove this, he poured freshly cooked bouillon into two glass flasks. He left one of them unlocked, on the other he put a double-curved glass tube, a so-called fermentation tube, which allows gas to be exchanged with the environment, but prevents particles from entering. He boiled the bouillon again in both glass flasks and then observed the development of the contents of both flasks over a longer period of time. The contents of the unsealed flask spoiled more quickly, while the bouillon in the flask with the fermentation tube remained edible for a longer time.

Pasteurization of milk and dairy products

The best known is the pasteurization of milk, which is heated to 72 to 75 ° C for 15 to 40 seconds and then immediately cooled again. Pathogenic germs in the milk are killed in the process. However, some natural flora remains. So it is not aseptic. Pasteurized milk stored at 6 to 7 ° C can be enjoyed unopened for about 6 to 10 days.

In Germany and the EU, European law (Council Directive 92/46 / EEC of June 16, 1992 Sanitary regulations for the production and marketing of raw milk, heat-treated milk and milk-based products) Pasteurization is required by law for all traded milk types except raw and preferred milk, raw milk cheese must be labeled as such and, in the opinion of many medical professionals, should be avoided as a preventive measure by pregnant women and people with weakened immune systems. In Australia and New Zealand, with a few exceptions such as Roquefort, only pasteurized or thermized dairy products have been allowed on the market since 1994.

Other uses

Other foods such as wine, fruit juice or beer are also often pasteurized by the food industry or made from pasteurized ingredients and put on the market. In combination with pasteurization, acidic products with a pH value of less than 4.5 can be preserved in such a way that refrigerated storage is not necessary. This group includes many fruit and vegetable juices or canned foods.

In addition to food, other products can also be pasteurized, such as sewage sludge or liquid manure.

Alternative procedures

Other methods of preservation are sterilization, ultra high temperature heating, boiling down, tyndallization and thermization.

Category: Food Chemistry