category: food preservation

Pasteurization, de.: Pasteurisation, Pasteurisieren, fr.: pasteurisation, it.: pastorizzazione, es.: pasteurización

Pasteurization is named after the French chemist Louis Pasteur (1822 - 1895). It is a process to prolong the expiration date of mostly liquid foods. In this process liquids are heated to a temperature below 100°C for a short time. This temperature differs depending on the used method and pasteurized food but never lies above 100°C. Pasteurization is used for foods where longer heating (as for example in sterilization) would negatively affect proteins, vitamins, minerals or colour.

Pasteurization removes most heat-sensitive microorganisms such as yeasts or moulds. Pasteurized foods are not sterile though, microorganisms are only reduced but not killed completely. Therefore they keep longer but are still perishable.

Pasteurization is for example used for milk, pickles, fruits and fruit juices. The process is best for foods that are supposed to be "fresh", and only keep for a certain time or for sour products with a pH level of 4.5 and below. Products with a pH of 4.5 and below are usually pickles and keep quite well. Sterilization does not take more time than pasteurization, only the temperature is higher! The heating time is determined by the heat transfer in the product (convection - conduction). Beer is pasteurized to kill the yeast needed in brewing.

Pasteurizing solid foods

The necessary temperature for pasteurization is only specified for milk. For pickles no specific temperature is determined. Foods are heated in open systems that cannot get hotter than 100°C.

Pasteurizing milk

The pasteurization of milk kills not only microorganisms but also lactobacillales. These bacteria contribute to the curdling of fresh milk. Pasteurized milk is easier to digest.

There are three pasteurization techniques:

• High temperature/short time (HTST) at 62 - 65°C for 30 minutes
• Batch pasteurization at 72 - 75°C for 15 to 30 seconds
• Higher heat/shorter time (HHST) at 85°C for 4 to 10 seconds