Almost all of the milk that is sold to consumers is pasteurized. This is done to increase the shelf life of the milk and to remove or slow the growth of harmful microorganisms (bacteria, fungi etc.). Pasteurization has been used since the 12th century in China, but the modern methods were created by Louis Pasteur in 1862. The pasteurization of milk was invented by Franz von Soxhlet in 1886. Today there are various different techniques used depending on the desired shelf life of the product.
How is milk pasteurized?
The most common form of pasteurization is used to treat the milk found in the refrigerator at your local store. This milk has a shelf life of about 2-3 weeks and is treated with a process called High Temperature Short Time (HTST). This is also known as Flash pasteurization, where milk is pumped through tubes where it is heated to 71.7 °C (161 °F ) for about 15-20 seconds. It is then quickly cooled and is ready to be bottled. Some countries now require the temperature to be slightly higher for this process and 72 °C has been made the minimum temperature set by the national food safety agencies.
For long life milk, also known as UHT milk, is treated with a process called Ultra-high temperature processing (also known as UHT or ultra-heat treated). As the name suggests, this milk is heated to 135 °C (275 °F) for at least 1 second. This is effective in killing microorganisms in the milk and means that this milk has a long shelf life. In fact, it can be stored unrefrigerated for 6-9 months. This type of milk is popular in Europe and is gaining popularity in many other countries, but the consumers from the United States have been resistant to purchasing unrefrigerated milk.
Disadvantages of pasteurized milk
The advantages of pasteurization are obvious, but there are also some concerns. For example, the process does not destroy harmful microorganisms that are heat resistant. Pasteurized milk is also lower in some vitamins, enzymes and beneficial bacteria. However, no viable alternative to pasteurization has been developed.