which has been found in multiple herds of cows around the US.

Not only that, but there have so far been at least three cases of bird flu in humans in the US this year, all of them in dairy workers working with infected cows.

But recent work from the FDA found that pasteurization can inactivate the virus in milk and inactivated viral particles have been found in pasteurized commercial milk from multiple states, but none of it contained active virus, because pasteurization likely inactivated it.

But what does pasteurization do to the milk?

Cow's milk contains water, proteins, sugars like lactose, lipids and minerals, and vitamins like riboflavin and phosphorus and B12, et cetera, et cetera, et cetera.

It does a body good, you know the drill.

It's technically an emulsion of oil in water with fatty droplets suspended in water.

All of those proteins and lipids and minerals and good stuff mean that it is an incredibly flexible food product.

Milk proteins are split into two main categories, casein and whey.

Casein is a family of related insoluble proteins that in milk often exists in a colloidal super molecule called a casein micelle, basically, they stick together in little hydrophobic clumps.

Casein is the main protein in most cheeses too, that gives them their structure.

Whey is also a family of proteins, this time soluble proteins, and we typically hear about them as the byproduct of cheese making.

There's a bunch of stuff in whey, alpha lactalbumin, beta lactoglobulin, immunoglobulins, soluble protein stuff.

When we pasteurize milk, we're also exposing the casein and the whey to heat and denature them.

Studies show that heating milk at high temperatures for long periods of time, denatures whey proteins, so that they can not only react with each other, but also with casein creating bigger globules of proteins.

But what happens at pasteurization temperatures and times?

A really nice study out of Brazil looked at side-by-side samples of raw, pasteurized and sterilized or ultra high temperature treated milk from a dairy factory in Brazil.

They looked at all kinds of potential changes in the milk, from moisture content to lactose content to calcium and other mineral and vitamin content, pH measures, fatty acid profile, you get the picture.

They found that protein, lactose, calcium, and phosphorus content stayed similar in the heat treated milks.

Homogenization and heat treatment seemed to disrupt the membrane of the fat globules, but overall, fatty acid profiles stayed relatively unchanged.

The pH was slightly increased, which reduced the amount of whey proteins associated with the casein micelles, but overall, these changes were small, really small.

One of the biggest changes after pasteurization was the decrease in total bacterial count.

Again, please don't drink raw milk, it is not worth it.

But there are some cheeses that are made with raw milk, and by the way, there are so many kinds of cheeses in the world, I'm going to have to generalize a little bit in some areas, so I apologize if I've left out your favorite epoisses or mimolette, mim-oh-lay?

I don't even know.

Mimolette.

The short version of cheese making is to turn warm milk into a lump of solid or solid-ish protein and fat, first by adding acid, either from acid producing bacteria or a mixture of enzymes called rennet, or things like lemon juice or citric acid for us home DIY-ers.

You can insert footage of me making mozzarella here.

It turned out okay.

This causes casein proteins to denature and start to clump together.

You can add more enzymes to further precipitate and break down the proteins, then remove the remaining whey liquid and then you could either heat it more or add mold spores or shape it or let it age, depending on the flavor that you want.

Now during my research into pasteurization, I went down like a cheese pull rabbit hole and I wanted to figure out how to make the best cheese pull and it turns out that pH is involved, so then I went out and I bought this like cheese pH meter, and that's gonna be just really useful in my kitchen all the time.

I'm just gonna test cheese pHs daily... New hobby.

pHs of a cheese can have big impacts on its texture.

The casein mesh that forms in the cheese making process is held together in part by calcium ions that allow it some give, gives a little stretch.

But the calcium can dissociate from the proteins if the acid level is too high.

So low acid cheese is like feta and goat cheese have lots of calcium gluing the casein together and they break really easily and they won't stretch.

But if the cheese has a higher acid content, like a gruyere or a blue cheese, the casein proteins can come apart too much and won't stretch well either.

You need a moderate acid cheese for a good cheese pull.

Now during cheese aging, the breakdown of fats in a process called lipolysis can help give cheeses their distinctive flavors.

Enzymes in the milk breakdown long fatty acids releasing free fatty acids that give cheeses their distinctive flavors.

For example, butyric acid, a very short fatty acid, is a common one and has a, "Baby vomit," or, "Rancid," scent distinctive of cheeses like provolone and feta.

I didn't come up with those descriptors.

But these free fatty acids can also produce buttery flavors, fruity flavors, all the good flavors that you want in cheese.

Lactose and proteins are also broken down in the ripening process and the resulting smaller sugars and amino acids can also carry their own flavors.

So does making cheese out of raw milk have any impact on this process?

And how do the proteins and lipids turn into something delicious?

The raw milk might have an impact on flavor.

Cheese connoisseurs often say that raw milk cheeses have more intense, stronger flavors, potentially due to higher levels of things like carboxylic acids, esters, and alcohols that come from fermentation of the milk by the microbiome of the raw milk.

But here's the thing, raw milk cheeses often have a high moisture content, a low acidity, and are aged at warmer temperatures, meaning that potentially pathogenic bacteria could thrive in the cozy warm cheese.

Here in the US, the FDA therefore stipulates that raw milk cheeses have to be aged for at least 60 days before being sold, with the idea that at this point, that cheeses would be too dry or acidic or salty for bacteria to thrive, giving time for all of that bad bacteria to die out before you eat it.

Again, if you suck all the water out of cells through evaporation or salt or denature their proteins with acid, they're not gonna be so good at making you sick anymore.

This makes a lot of sense for something like a raw milk cheddar, which gets hard and salty and inhospitable, but it makes a little less sense for a camembert, which keeps a pretty low acid and high moisture level.

Studies have shown that the levels of pathogenic bacteria do decrease in these kinds of cheese over time, but it doesn't always work.

And low levels of things like E. Coli, 0157:H7, and mycobacteria can still exist.

And in fact, just this year in 2024, there was an outbreak of E. Coli linked to raw milk cheddar sold in the US.

This is why some producers are arguing against the 60 day rule and for an approach that instead tests the cheese for pathogenic bacteria at multiple steps along the production pathway.

And this should probably apply to all cheeses!

Pasteurized milk cheeses can become contaminated during their production too, due to the fact that, again, you are letting a hunk of perfect microbial food sit around for a while before you eat it.

A CDC study looking at cheese related disease outbreaks between 1998 and 2011 found that of the 90 outbreaks, 42% happened in raw milk cheeses and 49% happened in pasteurized milk cheeses.

So should you swear off all raw milk cheeses because of the potential for contamination?

Honestly, I thought that I had, until I looked in my fridge and realized that a lot of the Parmesan and other cheeses I buy all the time are made with raw milk.

They're actually pretty common.

If aged properly, the risks of raw milk cheeses aren't zero, but they're low.

If you're out here eating things like oysters, which contribute to about 80,000 vibriosis cases per year, you're potentially at a higher risk of food poisoning from those than from raw milk cheese.

But not raw milk!

That is a much, much higher risk and just to really emphasize this point, in 1938, dairy was connected to 25% of disease outbreaks due to contaminated water and food, 25%.

Now that figure is down to 1%.

Pasteurization saves lives and stops the spread of preventable diseases and does not meaningfully change the nutritional value of the milk.

Stop it with the raw milk!

Stop it, stop.