Where does milk come from? Unless you live near a dairy farm it comes from the supermarket and it comes already homogenized and pasteurized. You know and use them, but what exactly do these two terms mean? Here’s what you should already know about milk.
When you see milk with only 2% fat you wouldn’t be criticized for thinking that 98% of the fat has magically been removed. But that would be wishful thinking because actually only about 50% of the fat has been removed, which is still a good thing. The fat content of cow milk varies by cow type, diet and other factors, but is usually somewhere around the 4% mark. I suppose that putting “2% fat” on the label is a lot more appealing than “50% less fat”. So why don’t they write “4% fat” instead of “whole” milk? I guess that’s why I’m not in advertising.
If you leave fresh cow’s milk standing for 12 to 24 hours it will separate with a high-fat cream layer rising above a low-fat milk layer because milk fat is less dense than water (thus, “cream rises to the top”). To prevent this separation, milk can be homogenized. Homogenization is when milk is pumped at high pressures through very narrow tubes to break up the fat globules, making it more difficult for them to separate from the rest of the milk. The smaller fat globules are however more vulnerable to being broken down further by enzymes in the milk, which can produce a sour taste. Therefore homogenization goes hand-in-hand with pasteurization.
Pasteurization is a process that kills bacteria that can cause serious infections in humans. The process is named after French scientist Louis Pasteur who invented it in the nineteenth century. Milk is heated to a high temperature for short time and then immediately cooled. The standard process is 72 °C (note that water boils at 100 °C) for 15 seconds, which will render milk safe to drink for up to three weeks. Some vitamins and minerals are also lost, but the health benefits of pasteurization far outweigh the lost nutrition.
Taking it a step further is UHT or Ultra Heat Treatment milk. Homogenized milk is heated to 138 °C for up to three seconds and immediately cooled down and packaged. An unopened container of UHT milk can last for up to six months without refrigeration. There is an even further loss of vitamins and a noticeable taste difference compared with normal Pasteurized milk, but it’s good to have handy for emergencies.