Starch Agar is a solid medium used for the differentiation of microorganisms based on their ability to hydrolyze starch. Meat Extract and Peptic Digest of Animal Tissue supply nitrogenous compounds, while Starch is the source of carbohydrates. Its hydrolysis is seen as a colorless zone surrounding the colonies, while a blue or purple area indicates lack of hydrolysis. Agar is the gelifying agent.