By Harold McGee
Milk fat accounts for much of the body, nutritional value, and economic value of milk. The milk-fat globules carry the fat-soluble vitamins (A, D, E, K), and about half the calories of whole milk. The higher the fat content of milk, the more cream or butter can be made from it, and so the higher the price it will bring. Most cows secrete more fat in winter, due mainly to concentrated winter feed and the approaching end of their lactation period. Certain breeds, notably Guernseys and Jerseys from the Channel Islands between Britain and France, produce especially rich milk and large fat globules. Sheep and buffalo milks contain up to twice the butterfat of whole cow’s milk.