Alcoholic fermentation

The alcoholic fermentation is a Chemical reaction Exothermique which transforms fermentable Sucre S by Levure S into alcohol and Carbonic gas with release of Chaleur:

C ₆ H ₁₂ O ₆ ==> 2C₂H₅ OH + 2CO₂ + 22 calories.

Secondary products are formed: most important are the Glycérol, the Succinic acid , the acetic Acid and the pentanol.

This process is divided into three parts:

There exists a great number of yeast species used for the Fermentation. Most known is the Brewers' yeast. One can also use Moisissure S.

One obtains Ethanol, which may undergo beneficiation like Carburant of substitution or basic commodity for the Chemical industry and of solid residue . This last contains the vegetation wastes partially or not hydrolized and yeasts. It thus has a content increased of Protéine S and can be used for the animal Alimentation.

The interest compared to the traditional production of ethanol (C2H4 + H2O ==> C2H5OH) is that one uses biomass instead of using oil, and that the energy expenditure to produce ethanol by biological way is of 0.5 J per joule obtained in the form of ethanol, whereas it is of 2 J/J by the traditional way.

In the case of the Wine, sugars of the Must, under the action of yeasts are transformed into ethanol (the yeasts are microscopic mushrooms). The phenomenon is accompanied by a carbonic gas release and a rise in temperature.

The yeasts also produce:

of the secondary compounds: higher alcohols, Glycerol S (glycerin), Succinic acid, Acid acetic (it is the volatile Acidity)…
of the aromatic substances: odors of Banane, of English candies, which take part in the characteristics of the wines early products (Beaujolais wine, Coteaux of the Lyonese, Gamay de Touraine…)

The flavors resulting from the Grape or varietal Arôme S are known as primary educations; they are known as secondaries when resulting from fermentation; those which develop during the breeding or of the evolution in Bouteille, are known as tertiary sectors.

The yeasts omnipresent in nature, are stuck on the Pruine of the skin of the grape, on the wine material of the wine storehouses. When they are of poor stock or of insufficient number, the vinificator with recourse to addition of yeast.

Alcoholic fermentation can occur only under certain conditions:

Temperature:

too cold (10°C), the process is very slowed down even incomplete
too hot (32 36 ° C), the yeasts die, the medium becomes inapt for their survival

Oxygen: Although fermentation is an anaerobic phenomenon, the yeasts need oxygen to multiply

Alcohol: It is a Antiseptique, even for the micro-organisms which produced it. Passed a certain concentration (of 14 with 16°), it acts like a Poison for yeasts. The drinks moreover alcoholic high degree are produced by Distillation.

See too

Fermentation of the beer

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