xanthan gum is a polysaccharide (a complex form of sugar). it is added to certain foods, such as salad dressings, to make them thicker. it is also added to cosmetics to keep the ingredients from separating. to make xanthan gum, workers add a kind of bacterium, "xanthomonas campestris", to glucose or sucrose. they let the mixture ferment for a while, and then add isopropyl alcohol to separate the polysaccharide from the mixture. they dry the polysaccharide, grind it into a powder, then add it to a liquid. the xanthan gum is then ready to use.