Milk protein consists of 80% casein and 20% whey protein. There are four major types of
casein molecules: alpha-s1, alpha-s2, beta, and kappa. Milk, in its natural state, is
negatively charged. The negative charge permits the dispersion of casein in the milk.
Precipitation of casein can be done using acid or rennin.
When an acid is added to milk, the H+ concentration neutralizes the negatively
charged casein micelles. At pH 4.7, the isoelectric point (the point at which all
charges are neutral) of casein, an isoelectric precipitate known as acid casein is