Heat treatment and pasteurization

March 11, 2022
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This page describes the purpose of pasteurization and the pasteurization conditions used in milk processing. The history of pasteurization provides the background for the implementation and benefits of pasteurization, as well as the basic principles of the conditions used.

Purpose of pasteurization
Improve the safety of consumers' milk by destroying the possible pathogenic microorganisms in milk. Improve the quality of milk products by destroying spoilage microorganisms and enzymes that reduce the quality and shelf life of milk.

Pasteurization conditions
Coxiella burnetii is an organism that causes human Q fever. It is recognized as the most heat-resistant pathogen in milk. Milk can be pasteurized using a treatment time and temperature higher than the minimum temperature required.
Pasteurization can be carried out in batches or continuously. Barrel pasteurizer consists of a closed barrel with temperature control. The milk is pumped into the cylinder, the milk is heated to the appropriate temperature and maintained at that temperature for an appropriate time, and then cooled. The cooled milk is then pumped out of the barrel and transported to other processing lines, such as filling stations or cheese barrels. Batch pasteurization is still used in some smaller processing plants. The most commonly used process for liquid milk is the continuous process. The milk is pumped from the raw milk silo to a storage tank, which sends the milk to the continuous pasteurization system. Milk continuously flows out of the tank through a series of thin plates, which heat the milk to the appropriate temperature. The milk flow system is set up to ensure that the milk is maintained at the pasteurization temperature for an appropriate period of time before flowing through the cooling area of the pasteurizer. The cooled milk then flows to the rest of the processing line, such as the filling station. There are many choices of temperature and time for continuous processing of frozen liquid milk. Although processing conditions are defined for temperatures above 200 ° F, they are rarely used because they give the milk an unwanted cooking flavor.

Pasteurization history
The health benefits of heating or boiling milk have been recognized since the early 19th century and were used to reduce infant milk borne diseases and mortality in the late 19th century. With the industrialization of society at the turn of the 20th century, the increase of milk production and distribution has led to the outbreak of milk borne diseases. With the commercialization of pasteurization and the improvement of dairy farm management practice, these diseases have actually been eliminated. In 1938, dairy products were the source of 25% of food and water-borne diseases, which can be traced back to the source, but now they account for far less than 1% of all food and water-borne diseases.
Pasteurization is the process of heating a liquid below its boiling point to eliminate microorganisms. The grade a pasteurized milk Ordinance (PMO), administered by the U.S. Department of health, the Department of human services and the Department of public health, and the food and drug administration, defines pasteurization standards for dairy and processing plant design, milking practices, milk handling, hygiene, and grade a dairy products.

The initial pasteurization condition is called rapid pasteurization. The milk is heated to 155 to 178 ° f (68.3 to 81 ° C) for a moment and then cooled. The pasteurization conditions were adjusted to 143 ° f (61.7 ° C) for 30 minutes or 160 ° f (71.1 ° C) for 15 seconds to inactivate Mycobacterium bovis.

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