Another question came in yesterday, asking what effect pasteurization has on cream, and more than that what effect ultra-pasteurization has. The answer is that any time you heat milk or cream up to any significant degree, you change its flavor. This results in a denaturing (science speak for “messing up”) of the whey proteins, which are partly responsible for milk’s flavor. That’s not to say pasteurization is a bad thing, it isn’t, for contrary to what a lot of raw milk advocates will tell you, milk can indeed become contaminated with a variety of microbes, some of which can make a person seriously ill. I’d never recommend buying any unless you are intimately familiar with the source (as in, you invite the cow over for cocktails on Saturdays).
Still, there are degrees of pasteurization, the general rule being that the lower the temperature the milk has been pasteurized at, the better. Standard pasteurization heats large batches of milk slowly to 145 degrees Fahrenheit for about 30 minutes. That’s enough to kill off anything dangerous, and ensure the milk is good for up to 18 days. The next step is known as high-temperature, short-time pasteurization, or HTST, in which a thin stream of milk is exposed to a more powerful heat source, raising its temperature to 162 degrees for 15 seconds. This process not only denatures some 10% of the proteins in milk, it creates a smelly gas know as hydrogen sulfide, imparting an off flavor that some people describe as “cooked”. Beyond that there’s ultra-high temperature pasteurization, or UHT, which heats milk to up to 300 degrees for just one second. It creates the effects you’d expect, though on the upside it allows the milk to be stored for fifty days or more without spoiling (very handy in an era where big dairies might be hundreds or even thousands of miles from their customers).
Personally, I think there’s a gigantic difference in taste between milk that’s merely pasteurized and either HTST or UHT milks. Where cream is concerned, there’s much less of a difference. The reason for that is because cream has far less protein in it than milk does, about 80% less. That means much less denaturing of those proteins, and fewer off flavors. I therefore won’t hesitate to buy ultra-pasteurized cream. Would I buy the plain pasteurized stuff if I could? You bet I would. But the fact is that merely pasteurized dairy products can be very hard to procure, even from many local dairies.