Milk

Milk is a complex suspension engineered by mammals as a complete food for rapid growth. For the cook, it’s an emulsion of fat in water stabilized by phospholipid membranes, with two fundamentally different protein families that govern most of its behavior under heat and acid.

Composition

Cow milk is roughly 87–90% water, with the remainder split between fat (3.6–5.2%), protein (3.0–3.9%), lactose (4.8–4.9%), and minerals (0.7–0.8%). These proportions vary significantly by breed — Jersey cows produce the richest milk (5.2% fat), while high-volume Holsteins are leaner (3.6%). Sheep milk is dramatically richer than cow milk (7.5% fat, 6.0% protein), and buffalo milk richer still (6.9% fat), which is why mozzarella di bufala and pecorino have such different characters from their cow-milk equivalents.