In milk, the fats form an emulsion with water, in which they are dispersed in small droplets. They stabilize the fat droplets by surrounding them with a water-favoring sheath. Coagulation of the droplets occurs because of a protein present in the milk, which links the droplets together and, as they coalesce, they form a head of cream. The skin is moderately impervious to steam, and enough pressure can build up beneath it to cause the milk to overflow from the vessel. Some of the protein is destroyed and creaming is reduced by heating the milk briefly to about 100 degrees C. Cream on the top of milk is less commonm now that homogenized milk is widely available.
Homogenized milk is formed by forcing milk through small openings under pressure.
This breaks the fat globules into smaller particles, resulting in a more viscous, whiter, blander tasting, and more stable emulsion. After incubation, the cream is churned. This breaks down the sheaths around the fat droplets, and they coalesce into a soft, solid mass. You may be able to smell butanedione by sniffing your armpits or someone's unwashed feet, because it is a contributor to the odor of fermenting perspiration. Deodorants act by killing the bacteria.