Processing Methods for Pasteurized Milk
Pasteurization is the process by which dairy products are heated to destroy various pathogens, or bacteria. Almost all milk and dairy products in the United States and Canada are pasteurized now, with various unpasteurized cheeses and milk often being illegal. There are four basic methods in the modern world used to pasteurize milk.
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Batch Method
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The batch method, also called the vat method, is the oldest form of pasteurization. It is not used as often as the HTST method, which is mentioned below. With the vat method, a large tank of milk is heated to 155 degrees Fahrenheit (69 degrees Celsius) for 30 minutes. The batch of milk is constantly stirred to make sure all parts of it are heated properly. This method is mainly used on milk that will be used for cheeses, ice cream, buttermilk and yogurt.
High Temperature Short Time Pasteurization
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High temperature short time (HTST) pasteurization is the most common type of pasteurization in the United States. Metal plates and hot water are used to quickly heat milk to at least 161 degrees Fahrenheit for no less than 15 seconds. The milk is then rapidly cooled. This is a process that is much faster and energy efficient than the batch method, but some critics claim that it gives the milk an overcooked taste. HTST can process large amounts of milk in short periods of time, which is the main reason that it is the most commonly used method of pasteurization.
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Higher Heat Shorter Time
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Higher heat shorter time is actually a variant of high temperature short time pasteurization. The equipment used to heat the milk is different, and the difference is that the milk is heated to a much higher temperature and remains there for a short period of time. Milk processed by the higher heat shorter time method can be ultra pasteurized, which means it is heated to no less than 280 degrees Fahrenheit. Ultra pasteurized products have a much longer shelf life than other types of pasteurized milk, but they still require refrigeration.
Aseptic Processing
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Aseptic processing is also called ultra high temperature (UTI) pasteurization. The milk is heated using sterile equipment, and then the pasteurized milk is aseptically put into sealed packaging. This packaging is hermetically sealed, which means it is air tight. The entire process is aseptic, which is where it gets its name, and that means that the milk is treated in such a way that it is free of microorganisms. The results of this type of processing are that the milk does not need to be refrigerated until after it is opened. Temperature and processing time varies according to the exact products being made and the specific type of equipment being used.
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References
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