<P> Fermentation is sometimes carried out in two stages, primary and secondary . Once most of the alcohol has been produced during primary fermentation, the beer is transferred to a new vessel and allowed a period of secondary fermentation . Secondary fermentation is used when the beer requires long storage before packaging or greater clarity . When the beer has fermented, it is packaged either into casks for cask ale or kegs, aluminium cans, or bottles for other sorts of beer . </P> <P> The basic ingredients of beer are water; a starch source, such as malted barley, able to be saccharified (converted to sugars) then fermented (converted into ethanol and carbon dioxide); a brewer's yeast to produce the fermentation; and a flavouring such as hops . A mixture of starch sources may be used, with a secondary starch source, such as maize (corn), rice or sugar, often being termed an adjunct, especially when used as a lower - cost substitute for malted barley . Less widely used starch sources include millet, sorghum and cassava root in Africa, and potato in Brazil, and agave in Mexico, among others . The amount of each starch source in a beer recipe is collectively called the grain bill . </P> <P> Water is the main ingredient of beer, accounting for 93% of its weight . Though water itself is, ideally, flavorless, its level of dissolved minerals, specifically, bicarbonate ion, does influence beer's finished taste . Due to the mineral properties of each region's water, specific areas were originally the sole producers of certain types of beer, each identifiable by regional characteristics . Regional geology accords that Dublin's hard water is well - suited to making stout, such as Guinness, while the Plzeň Region's soft water is ideal for brewing Pilsner (pale lager), such as Pilsner Urquell . The waters of Burton in England contain gypsum, which benefits making pale ale to such a degree that brewers of pale ales will add gypsum to the local water in a process known as Burtonisation . </P> <P> The starch source, termed as the "mash ingredients", in a beer provides the fermentable material and is a key determinant of the strength and flavour of the beer . The most common starch source used in beer is malted grain . Grain is malted by soaking it in water, allowing it to begin germination, and then drying the partially germinated grain in a kiln . Malting grain produces enzymes that convert starches in the grain into fermentable sugars . Different roasting times and temperatures are used to produce different colours of malt from the same grain . Darker malts will produce darker beers . Nearly all beer includes barley malt as the majority of the starch . This is because its fibrous hull remains attached to the grain during threshing . After malting, barley is milled, which finally removes the hull, breaking it into large pieces . These pieces remain with the grain during the mash, and act as a filter bed during lautering, when sweet wort is separated from insoluble grain material . Other malted and unmalted grains (including wheat, rice, oats, and rye, and less frequently, corn and sorghum) may be used . Some brewers have produced gluten - free beer, made with sorghum with no barley malt, for those who cannot consume gluten - containing grains like wheat, barley, and rye . </P>

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