Milk is composed of many proteins. The main groups are casein and whey proteins. Caseins are very digestible when compared to otherfood proteins, making it a very important human food. Casein is negatively charged in its natural state. This negative charge permits the casein to disperse in milk. When you add an acid, the H+ concentration neutralizes the negatively charged casein. When you acidify milk, its pH is allowed to reach 4.6, which brings casein to its isoelectric point. The isoelectric point is the point at which all charges are neutral. When casein loses its negative charge, it precipitates as curds. This acid casein is the basis forthe manufacture of cottage
cheese and cream cheese. Acid casein is also used in the chemical industry; in the production of adhesive products, textiles, and cosmetics; and as a binding agent in food products.