Milk, Cream, and Homogenized Milk

Cow’s milk contains 3.5 percent total fat, primarily in the form of small globules that are on the order of 5 micrometers in size, but that can be as small as 0.1 micrometer and as big as 10 micrometers. The fat globules are less dense than water, and after the milk has been cooled for twelve to twenty-four hours, they will float to the top as cream. This process is rapid because it is enhanced by the tendency of the fat globules to bind to whey protein. It would take much longer for small globules to rise to the surface. Cream forms on milk from goats and sheep much more slowly because the fat globules are smaller and it is harder for them to bind together.