Casein Acid Hydrolysate is a hydrolysate of Casein prepared by its reaction with hydrochloric acid at high temperature and pressure followed by a neutralization with sodium hydroxide. Casein is the main protein of milk, and a rich source of amino nitrogen. It is very rich in amino acids and contains a small amount of L-Cystine. Tryptophan and vitamins are destroyed by the acid treatment. It is used as a source of nitrogenous compounds in microbiological culture media.