🧪 Casein

Casein is the main protein in milk. In cow's milk it makes up about 80% of all the protein. In milk it floats as tiny clusters called micelles. Calcium holds them together. These clusters are what make milk white and cloudy.

Casein is the basis of cheese and cottage cheese. If rennet is added to milk, the casein clusters stick together into a firm curd. If milk goes sour and becomes acidic enough, casein also separates out in flakes; that is how cottage cheese is made. Everything that does not become curd goes into the whey. Human milk has much less casein than cow's milk, and in a baby's stomach it forms a soft curd.

Casein is not only used in food. It was used to make glue, paints and even a plastic called galalith, which was used for buttons in the 20th century. Casein is one of the main milk allergens: allergy to it is more common in young children. There is “A2” milk, which has a different form of beta-casein. A 2009 EFSA review found no clear link between ordinary A1 casein and chronic diseases.