# Fermentation

The fermentation is a biochemical reaction consisting in releasing from energy starting from Sucre (of the Glucose most of the time). The science of fermentation is the Zymologie. Fermentation does not require a Dioxygène (Pasteur: “fermentation it is the life without the air”), it can thus take place in medium Anaérobie. It is distinguished, by its energy poor yield, of the cellular Respiration, which requires, it, of the Oxygène (medium Aérobie). During breathing, the final acceptor of the electrons coming from the reduced cofacteurs NADH, H+ are transferred to oxygen, whereas in the case of fermentation, the electrons are transferred to compounds from the metabolic ways, such as the pyruvate involving the formation of lactic acid or of ethanol following the organizations and the conditions of cultures.

More exactly, for the Wine, in fact the Levure S are on the Pruine which, after Pressurage (wine rosy white and ) or during the cuvaison (red wines) will transform the Sucre present in the bay S of Raisin into alcohol.

## History

Fermentation precedes the control by the man by the processes of this one, indeed the fruits ferment without any human intervention.

## Chemical reactions

One distinguishes two great types of reactions of fermentation by the nature of the products (waste) of the reaction.

### Ethyl fermentation

In the case of ethyl fermentation (or alcoholic), the reaction releases from ethanol:

$\ rm \left\{C_6H_ \left\{12\right\} O_6+2 \, ADP + 2 \, pi \ rightarrow 2 \, C_2H_5OH + 2 \, CO_2 + 2 \, ATP\right\}$

The Glucose, the Adenosine diphosphate (ADP) and the Phosphore produce ethanol, carbon dioxide and Adénosine triphosphate (ATP)

### Lactic fermentation

The lactic Fermentation, as for it, releases from the Lactic acid , one also names it (homolactic fermentation):

$\ rm \left\{C_6H_ \left\{12\right\} O_6+2 \, ADP + 2 \, pi \ rightarrow 2 \, C_3H_6O_3 + 2 \, ATP\right\}$

Glucose, adenosine diphosphate (ADP) and phosphorus produce Lactic acid and adenosine triphosphate (ATP).

This type of fermentation relates to in particular the transformation of fresh cheese or yoghourt milk.

As comparison, in the presence of dioxygene, breathing produces 36 molecules of ATP starting from a molecule of glucose, that is to say 18 times more than fermentation, but it mobilizes a more complex enzymatic apparatus (see the Cycle of Krebs). In all logic, fermentation is privileged as long as there exist great quantities of sugar and little oxygen. On the other hand, as soon as sugar rarefies and that oxygen is available, intervenes breathing (or specialized companies).

Let us note that there exist other types of fermentation (fermentation butyric, acetic, sulfitic,…).

The mixed acid Fermentation is another type of fermentation which relates to primarily the enterobacteries.

## Physiological roles

### Ethyl fermentation

The alcoholic Fermentation is carried out by many organizations (Bactérie S, Levure S) living in a permanent or occasional way in mediums deprived of oxygen. The property of certain yeasts to transform the Sucre into ethanol is used by the man in the production of alcoholic drinks and for the manufacture of the Pain. The ideal temperature of fermentation is of 35 °C with 40 °C.

The alcoholic drinks are obtained by fermentation natural of the sweetened solutions. It is about a natural chemical reaction (biochemical) obtained thanks to the micro-organisms (bacteria, moulds, mushrooms) and with the yeasts which thanks to their enzyme, the zymase, break up natural fruit juices into ethanol and carbonic gas bubbles.

The yeasts present at the surface of the fruits or are naturally added with musts (fruit juice) which one makes ferment.

Concretely, to cause the process of fermentation, it is enough to leave the fruit in contact with the air by taking care to crush the biological protective membranes (skin,…), which is done while crushing or by crushing the fruit. The yeasts suspended in the air are amply sufficient to produce the fermentation of the pulp in a few days. One can also add yeasts in order to accelerate this natural process, like that or brewers' yeast (of the bread) also, by maintaining the temperature in the surrounding of 37°C, fermentation occurs in approximately one hour.

### Lactic fermentation

The lactic Fermentation is very much used in cheese dairy. The yoghourts are obtained starting from boiled, cooled, sown milk with a stock definite of bacterium ( L. Bulgaricus for example) and incubated from 3 to 4 hours with 40 °C. The manufacture of sauerkraut is carried out by lactic fermentation in the presence of 2 to sodium chloride 3%. The process is stopped when the acid content lactic reaches approximately 1,5%. Lactic fermentation is favoured during the ensilage of the agricultural produce, because produced acidity prevents the development of other micro-organisms which can cause the putrefaction of the ensiled products. The presence of lactic leavens in the intestinal flora is very favorable to a good performance of the intestine. Lastly, during the anaerobic processes governing the muscular contraction, the glycogen which is a glycosylé polymer releases from glucose thanks to an enzyme, the glycogen phosphorylase, glucose joined then glycolysis and forms 2 equivalents of pyruvate. Those are then transformed into lactic acid by a lactase déshydrogénase, which is oxidized later on during the processes aerobic. Lactic fermentation is a chemical reaction being able to proceed in the event of deprivation of oxygen in the muscular cells. The Muscle S needing a great quantity of energy in the event of physical-activity, consume a great quantity of sugar and especially, of oxygen. Glucose and oxygen necessary to the cellular reaction of Respiration are stored in the cell and are renewed by blood circulation. The quantity of oxygen brought can not be sufficient, that is to say in the event of short and intense effort (taking into account the time between the flow of rest and the flow in full effort), or even whereas the maximum oxygen capacity is already reached (during the final sprint ), whereas sugar remains available; the muscular cells carry out lactic fermentation then to produce energy.

The increase in the concentration in ions lactates in the muscular cells is one of the reasons of tiredness after an intense activity. Indeed, these ions lactates change the intracellular pH and modify in fact the enzymatic operating conditions of the cell which cannot work any more correctly. It is also important to note that the production of these ions lactates is not related to the Crampe S as one can often read it.

## Industrial processes of fermentation

• For the wine grower, the four main objectives of the alcoholic Fermentation of a grape juice are the following:

1. To ensure complete and fast fermentation sugars.

2. To avoid the production of volatile Acidity during the first third of fermentation.
3. To avoid the production of sulfur compounds with unpleasant odors during all fermentation.
4. To lead to the aromatic and gustatory objective, in particular by the choice of selected yeast.

The control of the alcoholic Fermentation of a Moût of grape requires to control the factors influencing directly the life and the survival of a yeast population. They can be gathered around 13 point-keys whose control constitutes the good practices of fermentation.

• See also Fermentation of the beer.

• In the field of the treatment of the organic Waste and the production of renewable energy, there exists the Méthanisation. Methanisation makes it possible to transform any organic matter (organic pollution, manure, household waste fermentable) into Biogaz. It consists mainly of 4 phases:

1. Hydrolysis of polymers of sugars, proteins or lipids in monomers.

2. Acidogènese which allows the transformation of these monomers into volatile fatty-acids.
3. Acétogènese which produces acetate.
4. Méthanogènese for the production of methane and CO2.

## Sources

• Methanisation Site of information on methanisation and biogas
• sympatico.ca
• www.icv.fr

## More

Simple: Fermentation

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