What is fermentation?

We explain what fermentation is, what types of fermentation can be used and the different uses it has.

1. What is fermentation?

It is called fermentation to an incomplete oxidation process , which does not require oxygen to take place, and that throws an organic substance as a result. It is a catabolic process type, ie, transformation of molecules complex and simple molecules to generate chemical energy in the form of ATP (adenosine triphosphate).

Fermentation is a process of glycolysis (breakdown of the glucose molecule) that produces pyruvate (pyruvic acid) and that the lack of oxygen as a receptor of electron surplus NADH (nicotin adenine dincleótido) produced, used for this purpose an organic substance which must be reduced in order to reoxidate the NADH to NAD +, finally obtaining a derivative of the initial substrate that oxidizes. Depending on the final substance, there will be various types of fermentation.

This process was discovered by the French chemist Louis Pasteur , who described it as “Life without air” ( La vie  sans l’air ), since it can be carried out in the absence of oxygen by microorganisms such as  bacteria ,  yeasts , or Some metazoans and protists. In this process, then, neither the mitochondria nor the structures linked to the cellular respiration process are involved. 

Compared to aerobic respiration , fermentation  is not a very efficient method of obtaining energy : only 2 molecules of ATP are produced per molecule of glucose consumed, while breathing is obtained from 36 to 38.

However, it is carried out by various cells of our body to alleviate the moments of absence of oxygen, as occurs in muscle cells that ferment glucose when the oxygen intake is not enough to continue breathing.

2. Fermentation types

According to the substance obtained at the end of the fermentation process, we can classify it into:

• Alcoholic fermentation . Carried out mainly by yeasts, it produces from certain sugars an amount of alcohol ethanol, carbon dioxide and ATP. This is the process used to produce alcoholic beverages.
• Acetic fermentation . Own bacteria of the genus  Acetobacter , transforms ethyl alcohol into acetic acid, that is, alcohol in vinegar. It is, however, an aerobic process, so it can occur in wines exposed to the air .
• Lactic fermentation . It consists of a partial oxidation of glucose, carried out by lactic bacteria or by animal muscle cells (when they run out of oxygen to breathe). This process generates ATP but byproducts lactic acid, which produces, when accumulated, the painful sensation of muscle fatigue.
• Butyric fermentation . Discovered by Pasteur, it consists of the conversion of glucoses into butyric acid and gas, the latter gives it a typically unpleasant smell. It is carried out characteristically by the bacteria of the genus  Clostridium  and requires the presence of lactose.
• Fermentation  butanodiólica . It is a variant of lactic fermentation, carried out by enterobacteria that release carbon dioxide and generate butanediol, a colorless and viscous alcohol.
• Fermentation  Propionic . Acetic acid , carbon dioxide and succinic acid are involved in this process , and propionic acid, a corrosive substance with a pungent odor, is obtained from all of them.

3. Fermentation Uses

Numerous human industries take advantage of fermentation to obtain certain substances . For example, in the cheese food industries, propionic fermentation processes are carried out, or in the preservation of many types of foodstuffs the presence of lactic acid, which acts as a preservative, is due to lactic fermentation.

Something similar occurs with the alcoholic industry, both of wines, beers or other types of spirits, which require a manufacturing process involving alcoholic fermentation. On the contrary, if some liquors such as wine are left uncovered for a long time, the added oxygen will start the acetic fermentation and the drink will start to pick up.