[InclinedPlane]

There are actually three. Vat pasteurization is the oldest, it involves holding milk at 145 deg. F for half an hour. High temperature, short time (HTST) pasteurization involves bringing milk to 161 deg. F for 16 seconds. And Ultra-pasteurization, or the ultra high temperature (UHT) process, involves bringing the milk to 280 deg. F for 2 seconds.

Time is money, so vat pasteurized milk is more expensive than HTST milk which is more expensive than UHT milk. The downside of higher temperatures is that more of the flavor compounds tend to be destroyed in the process. This has a secondary effect of driving the milk producer towards lower milk quality, since it all tastes the same after the UHT process.