Homogenization of Milk

Fat is less dense than water, causing it to float to the top of milk. This results in the thick layer of yellowish cream that rises to the top of unprocessed milk. Homogenization prevents this separation of water and fat. The mechanical process of homogenization pumps the milk under a high pressure of 2,000 to 2,500 pounds per square inch through fine holes, which breaks up the fat globules. This decreases the fat globule size to less than 2 microns. The now very small droplets of milk fat are surrounded by a lipoprotein membrane, which prevents them from joining together and separating out. The liquid and fat components of the milk are now, in effect, homogenized.

Most milk in the United States is homogenized. This purely mechanical process has no effect on nutrient content; however, sensory changes do occur, resulting in a creamier texture, whiter color, and blander flavor. Homogenized milk also coagulates more easily, making puddings, white sauces, and cocoa more viscous. Its increased surface tension gives it a greater foaming capacity. Homogenized milk is also more prone to rancidity caused by oxygen being added to the double bonds of the unsaturated fatty acids. Pasteurizing milk before homogenization inhibits rancidity because the lipase enzymes responsible for breaking down fat are inactivated.