Fermentation

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Ethanol ("alcohol") results by conversion (anaerobic glycolysis) of sugar materials in presence of yeasts, a so-called "alcoholic fermentation", either as spontaneous fermentation from the ubiquitously existing yeast (Saccharomyces) or by addition of special yeast. The fermentation is the basis for the production of alcoholic beverages. However, by fermentation only alcohol concentrations to maximally 18 per cent by volume are attainable. High per cent beverages ("spirits") as well as bioethanol (as fuel replacement) are received by distillation.

The summary fermentation equation C6H12O6 -> 2 C2H5OH + 2 CO2 is only a rough summary of a complex reaction sequence which was already set up in 1815 by Lavoisier. In a glycolyse reaction sequence glucose is first phosphorylated with ATP (Adenosine triphosphate) in presence of the enzyme Hexokinase to the Glucose-6-phospate, which reacts with the enzyme Phosphofructokinase to Fructose-6-phosphate, which leads with further ATP to the Fructose-1,6-diphosphate. With the enzyme Aldolase two C3-components results: Glyceraldehyde-3-phosphate and Dihydroxyacetone phosphate. The further fermentation process results in a hydride transmission by means of NAD+ (Nicotinamide-adenine-dinucleotide) under oxidation to 3- and 2-Phosphoglycerine acid, which supply under elimination of water Phosphoenol pyruvate. Dephosphorylation with ADP (Adenosine diphosphate) results in Pyruvic acide, which forms acetaldehyde under development of CO2 (carbon dioxide), leading finally with NADH (reduced form of the NAD+) to ethanol. The total balance can be described by the "idealized fermentation equation":

C6H12O6 + 2 ADP + 2 H3PO4  -> 2 C2H5OH + 2 CO2 + 2 ATP + 2 H2O

In practice, grains, plants, fruits, or vegetables are combined with water to create a liquid blend mash containing Polysaccarides. These are splitten by Amylase into Oligosaccarides an finally fermented by Maltase the Monosaccarides, in particular Glucose. Alternatively, also a thermal splitting can take place via graduated boiling with hot water at 65 to 95 oC, or simply directly from sugar-containing raw materials, like grape juice mash. The actual fermentation takes place with approx. 20 oC by the enymes contained in yeasts under air exclusion, thus anaerobic conditions, for the avoidance of the acetic acid fermentation. Fermentation takes place under development of carbon dioxide, thus preventing the income of air, since it is specifically heavier than the oxygen of air. After 2-4 days approx. 6 to 10 per cent alcohol content is reached (special yeasts up to 18 per cent) and the fermentation finished by the death of the yeast. In order to obtain higher alcohol contents, a following distillation is necessary.