Pasteurization
What are some of the various heat treatments that are performed on milk prior to cheese making?
Milk Ecology
I’m no expert on food safety or food regulations. This post is intended to address the basics of pasteurization and its various forms.
Milk, fresh from the cow, is a treasure trove of microbes and enzymes. Some of these could impart desirable qualities to cheese during ripening and aging. Some of these could also impart undesirable qualities. It’s important to remember milk is a very good growth medium for many different microbes. If steps aren’t taken to ensure consistent high quality milk throughout the cheese making process, some undesirable microorganisms (like pathogens) could grow and proliferate.
TopPurpose
One purpose of milk pasteurization is to help ensure a safer milk supply. Without proper care and hygiene, baddies like Listeria monocytogenes, Campylobacter jejuni, Mycobacterium tuberculosis, and Coxiella burnetii could grow and proliferate. Heating milk upfront, before cheese making, lowers the levels and chances of these bugs taking root and growing down the line. Milk pasteurization isn’t a silver bullet that can absolutely prevent the presence and growth of these pathogenic microbes. Without proper care and hygiene anything can happen, crap in—crap out. Pasteurization can also help lower the numbers of undesirable spoilage microorganisms and enzymes.
Coxiella burnetii - a heat-resistant microbe that can be found in milk. Pasteurization aims at destroying this bug. Source: Wikipedia
Aside from safety, another reason pasteurization is used is to help with consistency. By pasteurizing milk, the “canvas” is being partially cleaned allowing for more control and predictability. Having fewer microbes, good or bad, in the starting milk could mean the cheese maker has a better idea of what is going to happen to his/her cheese. Another way to think about it: removing competition for the microbes the cheesemaker added.
With all that being said, heating milk not only destroys the bad, but can also destroy some good as well. There are desirable flavor-generating microbes and enzymes that may be knocked out by the pasteurization process. The cheese maker has to make a judgement call to determine what is best for the cheese and what the regulatory ramifications may be.
Pasteurization is sometimes used as a catchall term to describe a few different heat treatments. Read on…
TopHTST
High-Temperature Short-Time pasteurization is a pasteurization technique commonly used in large-scale cheese making facilities. This process is also called “continuous” pasteurization or sometimes “flash” pasteurization. The regulations prescribe that milk is heated to 72°C for 15 seconds. The machinery to accomplish this is very complex and expensive, which is why it isn’t seen in small-scale operations very often.
An example of a HTST setup
Source: Sprinkman
LTLT
Low-Temperature Long-Time pasteurization is a pasteurization technique commonly used in small-scale and artisanal operations. This process is also called “batch” pasteurization or “vat” pasteurization. The regulations dictate milk is heated to 63°C for 30 minutes. This process doesn’t use as complex of equipment as HTST pasteurization; it’s akin to heating a really big pot of milk.
An example of a LTLT setup
Source: Schuller
Thermalization
Thermalization is a heating step some cheese makers use on their milk prior to cheese making. Here the milk is heated, but not as hot or as long as in HTST or LTLT pasteurization. This milk is sometimes called “thermized” milk or “heat-treated” milk. Legally, this milk is still considered raw. A cheese maker would use this process as a compromise between the effects of pasteurized milk and raw milk. However, the cheese maker must still abide by the 60 day rule.
Top60 Day Rule
Raw milk cheeses (including those made with heat-treated milk, see above) must be aged for at least 60 days at 35°F or higher. The idea behind this is that 60 days would allow enough time for some of cheese’s built-in safe guards to combat any potential growth of harmful microbes. Some of these safe guards include: acid development, salt content, and competing bacteria. All of these can help keep cheese safe from potential pathogen growth to some degree. But again, there is no substitute for high quality milk and good manufacturing practices.
Many young/fresh cheeses traditionally made with raw milk may not be optimal after 60 days
Source: Wikipedia
UHT
Ultra-High Temperature milk is not used for cheese making. UHT milk is sometimes called “Ultra Pasteurized” milk. In this process, milk is heated much more harshly than in the other processes we have discussed. This intense heat treatment usually means the milk has a longer shelf-life and can be shelf-stable when aseptically packaged. The intense heat used in this process can negatively affect the structure of milk causing cheese making to be impractical. A side effect of this intense heat treatment can be seen in UHT milk near the end of its shelf-life, age gelation.
Shelf-stable dairy creamers are an example of UHT products
Source: Wikipedia
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