Difference between revisions of "Ethanol"

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=== Fermentation ===
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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
  
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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.
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: [[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>]]
  
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Ethanol is also a [[biofuel]] made from [[alcohol]] and is an [[oxygenate]] that is added to [[gasoline]] to increase the [[octane]] rating. The product is produced through the [[fermentation]] of [[corn]], or other cellulosic material.  
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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.
  
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==Process==
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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.
  
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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.
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==Co-products==
 
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A co-product of the fermentation process is [[distillers grains]] which can be used as cattle feed. Distillers grains is termed either [[wet distillers grains]] or [[dried distillers grains]] or simply [[DDGs]]. Wet distillers grains have a very short shelf life as they are susceptible to microorganisms that can pollute the material and render it unfit for cattle consumption.   
 
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==Ethanol Industry==
 
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In the [[United States]] ethanol is most commonly made through the fermentation of corn. Other countries, such as [[Brazil]] use sugar as a [[catalyst]] for the fermenting process. Currently, the US has the highest production numbers for ethanol in the world, but some analysts forecast China as being a potential world player in the ethanol market. [[China]] currently uses [[casava]] and [[wheat]] among other material for producing ethanol.  
 
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[[Category:Chemistry]]
 

Revision as of 20:44, April 5, 2007

Fermentation

Ethanol for use in alcoholic beverages, and the vast majority of ethanol for use as fuel, is produced by fermentation: when certain species of yeast (most importantly, Saccharomyces cerevisiae) metabolize 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

C6H12O6 → 2 CH3CH2OH + 2 CO2

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 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 grains, 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 enzymes that can break its starches into sugars.

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