Beer is produced by the brewing and fermentation of starches, mainly derived from cereals — the most common of which is malted barley, although wheat, corn, and rice are also widely used. Most beer is flavoured with hops, which add bitterness and act as a natural preservative, though other flavourings such as herbs or fruit may occasionally be included. Alcoholic beverages fermented from non-starch sources such as grape juice (wine) or honey (mead) are not classified as beer.