Fermentation
Main article: Ethanol fermentation See also: Yeast in winemakingEthanol for use in alcoholic beverages, and the vast majority of ethanol for use as fuel, is produced by fermentation. When certain species of yeast (e.g., Saccharomyces cerevisiae) metabolize sugar in reduced-oxygen conditions they produce ethanol and carbon dioxide. The chemical equations below summarize the conversion:
- C6H12O6 → 2 CH3CH2OH + 2 CO2
- C12H22O11 + H2O → 4 CH3CH2OH + 4 CO2
Fermentation is the process of culturing yeast under favorable thermal conditions to produce alcohol. This process is carried out at around 35–40 °C. Toxicity of ethanol to yeast limits the ethanol concentration obtainable by brewing; higher concentrations, therefore, are usually obtained by fortification or distillation. The most ethanol-tolerant strains of yeast can survive up to approximately 15% ethanol by volume.
To produce ethanol from starchy materials such as cereal grains, 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 mashed, the amylase converts the remaining starches into sugars. For fuel ethanol, the hydrolysis of starch into glucose can be accomplished more rapidly by treatment with dilute sulfuric acid, fungally produced amylase, or some combination of the two.
Read more about this topic: Chemical Derivatives Of Ethanol, Production
Famous quotes containing the word fermentation:
“Unquiet souls!
MIn the dark fermentation of earth,
In the never idle workshop of nature,
In the eternal movement,
Ye shall find yourselves again.”
—Matthew Arnold (1822–1888)
“Two principles, according to the Settembrinian cosmogony, were in perpetual conflict for possession of the world: force and justice, tyranny and freedom, superstition and knowledge; the law of permanence and the law of change, of ceaseless fermentation issuing in progress. One might call the first the Asiatic, the second the European principle.”
—Thomas Mann (1875–1955)
“A tree is made to live in peace in the color of day and in friendship with the sun, the wind and the rain. Its roots plunge in the fat fermentation of the soil, sucking in its elemental humors, its fortifying juices. Trees always seem lost in a great tranquil dream. The dark rising sap makes them groan in the warm afternoons. A tree is a living being that knows the course of the clouds and presses the storms because it is full of birds’ nests.”
—Jacques Roumain (1907–1945)