Pasteurization, used to slow microbial growth in food, is a process of heating food or liquid to a specific temperature for a definite length of time and then cooling immediately. Louis Pasteur was the creator of the process and completed his first test with Claude Bernard in April 20, 1864. The process was conceived as a way to prevent wine and beer from souring. Mostly, commercial-scale sterilization of food is uncommon due to its poor affects on taste and quality of product. Most dairy products are superheated to ensure toxic microbes are destroyed.
As first suggested by Franz von Soxhlet, in 1886, pasteurization is typically associated with milk. Although linked to food allergies it is the main reason that milk has such an extended shelf life. Milk that has been pasteurized through the High Temperature Short Time process gives the milk two to three weeks. Ultra pasteurized milk can last even longer with shelf lives up to two or three months. Ultra heat treatment along with sterile handling and aseptic packaging milk can be stored, un-refrigerated, for 6-9 months. However, ordinary milk should have a shelf life of only 10 to 16 days unopened.
If milk is brought to a boil it can cause curdling, therefore when pasteurizing milk it is usually brought to a temperature below boiling. There are three types of pasteurization although only two are typically used. High Temperature/Short Time and “Extended Shelf life” treatment are the two commonly used. During HTST milk is forced between metal plates or through pipes heated on the outside by hot water. Milk labeled pasteurized is treated with the HTST method. When labeled with “ultra-pasteurized” the milk has been treated with the UHT method.
National food safety agencies are usually in control of standardizing pasteurization methods. Milk must be HTST pasteurized in order to qualify for the “pasteurization” label. Depending on the fat content and the usage of the dairy product the standards can change. Canada’s standards require milk to be heated to at least 72 degrees Celsius for at least 16 seconds and then cooling it to 4 degrees Celsius.
HTST pasteurization is designed to kill 99.999% of the number of viable micro-organisms in milk. This is adequate for destroying almost all yeasts, mold, and common spoilage bacteria. The milk must be heated evenly, at a consistent temperature, and for the correct time for pasteurization to be successful.
Pasteurization has become the subject of increased scrutiny due to pathogens that are both widespread and heat resistant including one linked to Crohn’s Disease. However, pasteurization can prevent diphtheria, salmonellosis, strep throat, scarlet fever, listeriosis, brucellosis, and typhoid fever.