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Pasteurization of Milk

In the Introduction to Raw Milk blog, we briefly touched on pasteurization.  Here, we will cover the specifics of the process, and why it is a vital step in ensuring the safety of the foods you consume.  Pasteurized foods can become contaminated after the process if they are not handled properly (including kept refrigerated).   

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Milk flasks

Louis Pasteur, Father of Pasteurization

The process of pasteurization was developed by Louis Pasteur in France in 1862 to prevent the spoilage of beer and wine.  He then applied the same process to milk.  Many public health agents call this the second greatest break-through in preventing communicable diseases, just behind vaccinations.  Incidentally, Pasteur was also responsible for developing vaccines for rabies, small pox, tuberculosis, and anthrax.

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What foods can be pasteurized?

Pasteurization can be used for many food items.  The most familiar is milk.  Other foods, such as apple juice, sauerkraut, almonds, eggs, and vinegar are commonly pasteurized.  The process varies slightly, based on the type of food, and the desired end product.  The goals of pasteurization are to destroy any harmful microorganisms in the foods and to extend the shelf life of the products.  Pasteurization is not sterilization, so spoilage is delayed, but not eliminated.  The process destroys harmful microorganisms that cause milk to spoil, as well as inactivates lipase, which breaks down fat, leading to rancidity.  Processed correctly, foods do not lose any of their nutrient value.  We will discuss High-Temperature-Short-Time (HTST) Treatment, Low-Temperature-Long-Time (LTLT) Treatment, and Ultrapasteurization of milk.

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Pasteurization Steps

Current protocols for milk are set to destroy Coxiella burnetii (causative bacteria of Q fever).  Previous protocols were set to kill Mycobacterium bovis (causative bacteria of TB).  HTST pasteurization is 161°F (72°C) for 15 seconds.  LTLT pasteurization is 145°F (63°C) for 30 minutes.  Ultrapasteurization is 280°F (138°C) for 2 seconds. 

To get an idea of the steps in the process, we will walk through HTST, as this is the most common process used in commercial creameries.  First, the milk will pass through a clarifier.  A clarifier is a large centrifuge that is used to remove any solid material from the milk, such as blood or somatic cells.  It cannot remove small particles like bacteria.  The clarifier is sometimes used to separate the cream from the milk in the same step.

The next step is the HTST unit.  The milk will flow in pipes through the unit.  Milk is maintained at the specified temperature for the specified time.  As the milk flows out of the unit, it will pass by the regenerator plate.  This plate serves to cool the pasteurized milk and transfer the heat to the incoming raw milk. 

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Homogenization

The pasteurized milk then moves to the homogenizer.  Milk is pumped through small openings under high pressure.  This causes the fat globules to break into small particles that will remain suspended in the milk (the cream will not rise). 

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Effective Pasteurization

To ensure that the pasteurization process was effective, alkaline phosphatase is measured in the end product.  The time-temperature relationship for proper pasteurization will also inactivate alkaline phosphatase.  Therefore, this is an easy test to perform, instead of trying to culture the milk to determine if there are any viable bacteria.

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Enjoy a glass of pasteurized milk!

Milk safety has come a long way in the last 140 years.  You can rest assured that the milk you are enjoying is safe, wholesome, and delicious!

References

Hubbert, William T., et al. Food Safety and Quality Assurance: Foods of Animal Origin. 2nd ed., Blackwell Publishing, 1996.

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