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.