Xanthan gum is a polysaccharide secreted by the bacterium Xanthomonas campestris, used as a food additive and rheology modifier, commonly used as a food thickening agent (in salad dressings, for example) and a ster (in cosmetic products, for example, to prevent ingredients from separating). It is composed of pentasaccharide repeat units, comprising glucose, mannose, and glucuronic acid in the molar ratio 2:2:1. It is produced by the fermentation of glucose, sucrose, or lactose. After a fermentation period, the polysaccharide is precipitated from a growth medium with isopropyl alcohol, dried, and ground into a fine powder. Later, it is added to a liquid medium to form the gum.