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Milk Pasteurization Techniques

Louis Pasteur is considered the father of modern microbiology, and with good reason. We take it for granted today that microorganisms such as bacteria can cause disease, but it was Pasteur who both demonstrated this with irrefutable laboratory evidence, and developed techniques to combat microbe-borne disease. His first major success was single-handedly rescuing the French silk industry by identifying the microscopic culprits responsible for killing silkworms and developing techniques to keep the worms disease-free. He is, of course, even more famous for devising methods to kill disease-causing organisms in milk.

HTST
- The most common milk pasteurization procedure is high temperature/short time pasteurization, or HTST. In this procedure, milk is raised to a temperature of 72 degrees Celsius (161.5 degrees Fahrenheit) for a minimum of 15 seconds. If milk is labeled "pasteurized," it has most likely undergone HTST pasteurization. HTST pasteurized milk has a refrigerated shelf life of two to three weeks.
UHT
- UHT is ultra-high temperature pasteurization. Milk is brought to a minimum temperature of 138 degrees Celcius (280 degrees Fahrenheit) for at least two seconds. Milk must be treated with this procedure to legally be labeled "ultra-pasteurized." Ultra pasteurized milk has a much longer shelf life than HTST milk, and can still safely be consumed for up to two to three months
Sterilization
- It's important to make a distinction between pasteurization and sterilization. Sterilization is an effort to destroy all microbes present in a sample. Pasteurization aims to vastly reduce the number of viable microorganisms, but not to destroy them all, which would require a longer time and/or temperature and would entail undesired chemical changes. HTST pasteurization achieves a 5-log reduction (0.00001 times the original) in the number of viable microorganisms in milk.
Microorganisms
- Before Louis Pasteur developed the techniques that bear his name, the potential for food-borne illness in milk was very high. Some of organisms present in raw milk include Staphylococcus aureus, Mycobacterium tuberculosis, Salmonella, Coxiella burnetii and E. coli. Both UHT and HTST methods are considered sufficient to reduce the numbers of these organisms so that they do not present a significant threat.
Home Pasteurization
- Consumers who wish to pasteurize their raw milk at home can heat milk to 74 degrees Celsius (165 degrees Fahrenheit)) in a double boiler for 15 seconds while stirring constantly to ensure even heating. After 15 seconds have elapsed, they should cool it to 63 degrees Celsius (145 degrees Fahrenheit) by setting the top of the double boiler in cold water. They should cool it further by adding ice to the water until the temperature of the milk falls below 4 degrees Celsius (40 degrees Fahrenheit) Milk should be stored below 4 degrees Celsius until used. Home pasteurizers should not use a microwave oven. Microwaves may raise the average temperature to the sufficient level, but they do not produce even heating, and relying on the microwave to kill dangerous microbes may result in exposure and disease.

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