Yeast promotes alcoholic fermentation, consists largely of cells of a fungus (as the saccharomyces, Saccharomyces cerevisiae), and is used as a leavener in baking. It gives the characteristic flavor in bread and other yeast-leavened products. Dry, compressed, and cream yeast are all used in baked goods. Carbon dioxide is generated as a result of the breakdown of fermentable sugars in the dough. The carbon dioxide creates gas bubbles in dough within the protein matrix allowing it to rise. Dough maturation occurs by the chemical reaction of yeast-produced alcohols and acids on protein of the flour, and by the physical stretching of the protein by carbon dioxide gas. This results in the light, airy physical structure associated with yeast-leavened products. It gives the characteristic flavor in bread and other yeast-leavened products. It is activated with moisture and carbohydrates. It is most active at 35-40ºC (95-104ºF) and is inactivated at 55ºC (131ºF).