I’d been a raw milk drinker for years. Yet I hadn’t expected to respond so negatively to the glass of Horizon organic milk my friend poured for me. After all, that’s what I’d drunk for years before making the switch to raw milk from grass-fed cows.

“Yuck. This tastes burnt!” I said.

That’s when I saw it. The milk had been ultra-high temperature pasteurized. In fact, more than 80% of the organic milk sold in the U.S. is UHT pasteurized. It’s why I don’t drink most store-bought organic milk.

What is UHT Milk?

The official U.S. government definition of an ultra-pasteurized dairy product stipulates “such product shall have been thermally processed at or above 280° F for at least 2 seconds, either before or after packaging, so as to produce a product which has an extended shelf life.”

Get this. UHT milk has a shelf life of 6 to 9 months (until opened). When the world’s foremost UHT milk processor, Parmalat, first introduced UHT milk to the U.S. market back in 1993, they hit a snag. Americans distrust milk that hasn’t been refrigerated. We like our milk cold, and UHT milk doesn’t need to be refrigerated.

So, milk producers got creative. They could extend the shelf life of their product and not advertise that they were doing it. They’d sell the milk in normal packaging, in the refrigerator aisle, and none of us would be the wiser.

Now, almost all of the organic milk and the majority of conventional milk available in U.S. supermarkets is UHT processed.

What’s wrong with UHT processing?

The introduction to a 2005 study published in the Journal of Dairy Science highlighted the current problems with UHT processing from an industry point of view:

Often, heat treatment causes milkfat globule membrane proteins and whey proteins to unfold such that buried sulfhydryl (-SH-) groups, normally masked in the native protein, are exposed to the outer surfaces (Hoffmann and van Mill, 1997). In turn, these processes produce extreme cooked flavors, often attributed to changes in the sulfhydryl and disulfide content of the protein fraction (Swaisgood et al., 1987). Conventional pasteurization methods have long been in place and with the advent of UHT technology, the sterilization of fluid milk was achieved using higher temperature treatments for shorter periods. However, shelf-stable milk has met with limited acceptability by the consumer, especially in the United States, due in part to a high cooked flavor. Several attempts to improve the quality of UHT-treated milk products proved successful to varying degrees. Previously, Swaisgood and coworkers used immobilized sulfhydryl oxidase to reduce the thiol content of UHT-heated skim milk and described an improved flavor after enzymatic oxidation to form protein disulfide bonds (Swaisgood et al., 1987). Other studies have showed that altering UHT processing parameters, such as indirect vs. direct steam injection systems, cooling rates, and long-term storage conditions have a significant impact on sensory attributes (Browning et al., 2001). Most recently, epicatechin, a flavonoid compound, was added to UHT milk prior to heating, and the results revealed partial inhibition of thermally generated cooked aroma (Colahan-Sederstrom and Peterson, 2005).

So for decades, UHT processors have known that UHT processed milks results in a “high cooked flavor,” and they’ve done all kinds of experimenting to get rid of the nasty taste and smell (even resorting to adding flavonoid compounds to the milk to try to negate the off-flavor).

Okay, so it tastes funny compared to raw milk. And maybe it smells funny too. But what makes UHT processing any worse than regular old pasteurization?

Let’s start where the milk does — raw. The components of raw milk are extremely fragile. The milk proteins are complex and three dimensional, meant to be broken down when digested by special enzymes that fit into the proteins like pieces of a jigsaw puzzle.

When you rapidly heat milk, it denatures the proteins, flattening them so the enzymes can’t do what they’re supposed to do. In other words, it makes the milk protein significantly harder to digest! Look at what happens when milk is ultra-pasteurized at high temperatures versus when it is pasteurized at low temperatures:

“Whey protein denaturation plateaued at about 88% following a UHT heat treatment of 149°C for 10 s. However, it reached about 88% with a vat heat treatment of 82°C for 5 min and reached 95 to nearly 100% after 10 to 15 min. Vat processing under pasteurizing conditions at 63°C for 30 min resulted in less than 10% denaturation.” (source)

Now, that’s scary. No wonder more and more people are starting to think of themselves as intolerant to casein (the protein found in milk).

Not only do pasteurization and UHT processing kill off the enzymes present in milk needed to digest the casein, the casein itself is altered to the point of being indigestible!

So now you know why I don’t buy organic milk at the store — even when I run out of raw milk — unless it’s low-temperature pasteurized. If you want more help deciding how to prioritize your milk purchases, check out this post on Healthy Milk: What To Buy.