Homogenized milk is a type of milk that has undergone a process to mix and disperse milk fat globules in order to prevent milk from separating and give it a more homogeneous texture. The process of homogenization subjects the milk to high pressure to break up the fat globules, which become very small (less than 2 microns) and are covered by a membrane composed of lipids and proteins, as well as by casein micelles. This membrane prevents the fat from collecting at the surface of the milk and allows its permanent dispersion in a very fine emulsion. Homogenization creates a more uniform texture, a more pleasant flavor, and a whiter color. It also makes the milk creamy and prevents a layer of cream from forming in the milk, a quality that made homogenized milk popular with consumers as early as the 1920s. Homogenization gives milk a longer shelf life, better foamability, and improved capabilities as a cooking ingredient. The homogenization process is purely mechanical and does not affect the nutritional value of milk, but rather modifies its sensory characteristics. Most commercial milk sold in supermarkets is homogenized, and it is not mandatory for small dairy farms to homogenize their milk.