Beer is one of the oldest alcoholic drinks in the world​,​[1][2][3] the most widely consumed​,​[4] and the third most popular drink after water and tea.[5](p 1) Beer is produced by the brewing and fermentation of starches from cereal grains—most commonly malted barley​,​ although wheat​,​ maize (corn)​,​ rice​,​ and oats are also used. The fermentation of the starch sugars in the wort produces ethanol and carbonation in the beer.[6] Most modern beer is brewed with hops​,​ which add bitterness and other flavours and act as a natural preservative and stabilising agent. Other flavouring agents​,​ such as gruit​,​ herbs​,​ or fruits​,​ may be included or used instead of hops. In commercial brewing​,​ natural carbonation is often replaced with forced carbonation