The Germans are only allowed to use four ingredients when brewing beer, if they want it to conform to the country's beer purity law: malted grain (almost always barley), hops (a flower that serves as a flavoring agent), water and yeast. Malt determines the body of the beer, and it overall taste and mouthfeel. While barley is the grain used most often, wheat is also used in certain types of beer. Malt also provides the yeast with food in the form of sugar, which the yeast then transforms into alcohol and carbon dioxide.