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'''Ethanol''', also known as [[grain alcohol]] is a flammable [[chemical compound]] with a strong [[odor]], and is the [[alcohol]] found in [[alcoholic beverage]]s. In common usage, it is often referred to simply as alcohol. The chemical formula is variously represented as EtOH, CH<sub>3</sub>CH<sub>2</sub>OH, C<sub>2</sub>H<sub>5</sub>OH.
'''Ethanol''', also known as [[grain alcohol]] is a flammable [[chemical compound]] with a strong [[odor]], and is the [[alcohol]] found in [[alcoholic beverage]]s. In common usage, it is often referred to simply as alcohol. The chemical formula is variously represented as EtOH, CH<sub>3</sub>CH<sub>2</sub>OH, C<sub>2</sub>H<sub>5</sub>OH.
==Process==
==Process==
Ethanol for use in [[alcoholic beverage]]s, and the vast majority of ethanol for use as fuel, is produced by fermentation: when certain species of [[yeast]] (most importantly, ''[[Saccharomyces cerevisiae]]'') [[metabolism|metabolize]] [[saccharide|sugar]] in the absence of [[oxygen]], they produce ethanol and [[carbon dioxide]]. The overall chemical reaction conducted by the yeast may be represented by the chemical equation
: [[glucose|C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>]] → 2 CH<sub>3</sub>CH<sub>2</sub>OH + 2 [[carbon dioxide|CO<sub>2</sub>]]
The process of culturing yeast under conditions to produce alcohol is referred to as [[brewing]]. Brewing can only produce relatively dilute concentrations of ethanol in water; concentrated ethanol solutions are [[toxicity|toxic]] to yeast. The most ethanol-tolerant strains of yeast can survive in up to about 15% ethanol by volume.
During the fermentation process, it is important to prevent oxygen from getting to the ethanol, since otherwise the ethanol would be oxidised to [[acetic acid]] (vinegar). Also, in the presence of oxygen, the yeast would undergo [[aerobic respiration]] to produce just [[carbon dioxide]] and water, without producing ethanol.
In order to produce ethanol from starchy materials such as [[cereal grain]]s, the starch must first be broken down into sugars. In brewing [[beer]], this has traditionally been accomplished allowing the grain to germinate, or [[malt]]. In the process of germination, the seed produces [[enzyme]]s that can break its starches into sugars.