Editing Ethanol (section)

=== Fermentation ===
{{more citations needed section|date=November 2024}}
{{Main|Ethanol fermentation|Cellulosic ethanol}}
{{See also|Yeast in winemaking}}
Ethanol in [[alcoholic beverage]]s and fuel is produced by fermentation. Certain species of yeast (e.g., ''[[Saccharomyces cerevisiae]]'') metabolize sugar (namely [[polysaccharide]]s), producing ethanol and carbon dioxide. The chemical equations below summarize the conversion:

{{block indent|[[glucose|{{chem|C|6|H|12|O|6}}]] → 2 {{chem|CH|3|C|H|2|O}}H + 2 CO<sub>2</sub>}}
{{block indent|[[sucrose|{{chem|C|12|H|22|O|11}}]] + {{chem|H|2|O}} → 4 {{chem|CH|3|C|H|2|O}}H + 4 CO<sub>2</sub>}}

Fermentation is the process of culturing yeast under favorable thermal conditions to produce alcohol. This process is carried out at around {{convert|35|-|40|C|F}}. Toxicity of ethanol to yeast limits the ethanol concentration obtainable by brewing; higher concentrations, therefore, are obtained by [[Fortified wine|fortification]] or [[distillation]]. The most ethanol-tolerant yeast strains can survive up to approximately 18% ethanol by volume.

To produce ethanol from starchy materials such as [[cereal]]s, the [[starch]] must first be converted into sugars. In brewing [[beer]], this has traditionally been accomplished by allowing the grain to germinate, or [[malt]], which produces the [[enzyme]] [[amylase]]. When the malted grain is [[mashing|mashed]], the amylase converts the remaining starches into sugars.

Sugars for [[ethanol fermentation]] can be obtained from [[cellulose]]. Deployment of this technology could turn a number of cellulose-containing agricultural by-products, such as [[corncob]]s, [[straw]], and [[sawdust]], into renewable energy resources. Other agricultural residues such as sugarcane bagasse and energy crops such as [[switchgrass]] may also be fermentable sugar sources.<ref>{{cite web | last=Clines | first=Tom | name-list-style=vanc | title=Brew Better Ethanol | publisher=Popular Science Online | date=July 2006 | url=http://www.popsci.com/popsci/energy/6756226d360ab010vgnvcm1000004eecbccdrcrd.html | archive-url=https://web.archive.org/web/20071103083747/http://www.popsci.com/popsci/energy/6756226d360ab010vgnvcm1000004eecbccdrcrd.html | archive-date=3 November 2007}}</ref>