Butterfat, or Milkfat, the natural fat of milk. It is the chief component of butter. Butterfat is composed mostly of a mixture of triglycerides, chemical compounds that contain fatty acids; the triglycerides in butterfat contain saturated fatty acids. It also contains vitamins A, E, and K. Butterfat forms small, round droplets or globules, 1/15,000 to 1/2,500 of an inch (.0017 to .01 mm) in diameter. They can be seen in milk placed under a microscope. Because butterfat has a density less than that of the other components of milk, it tends to rise to the top of a container of ordinary milk to form cream. In homogenized milk, the cream does not separate because its globules of butterfat have been broken up into extremely small droplets, forming a colloid.

Dairy farmers judge the "richness" of milk by its percentage of butterfat. The butterfat content is the main factor that determines the price—the more butterfat, the higher the price. Milk from different breeds of cattle contains a varying percentage of butterfat. Jersey milk, the richest, contains about 5.3 per cent. Dairy farmers regularly test the butterfat in the milk of their cows.