Beer is a low-alcohol beverage made by malting cereals (principally barley), adding flavor with hops and then fermenting the mixture. Yeast is added to start the fermentation process, which results in alcohol and carbon dioxide. The carbon dioxide, which is not allowed to escape, results in the characteristic fizz. Since beer has a high percentage of water, the quality or the source of the water plays a major role in the flavor and character of beer. There are many types of beer including lager, light, ale, stout and porter. Beer is used in cooking to add flavor to stews, soups and breads.