What is Fermentation?

Fermentation can be explained in a number of ways. This article will elaborate the process of fermentation as a technique of biochemistry. The term fermentation has been derived from the Latin word “fervere” that simply means “to boil”. In biochemistry, fermentation is a technique of deriving energy from the oxidation of various organic compounds, like carbohydrates.

This process involves the use of an organic compound as an endogenous electron acceptor. This is exactly opposite to the process of respiration where the donation of electrons takes place by an exogenous electron acceptor (for example—oxygen) through an ETC i.e. electron transport chain.

The process
Louis Pasteur (French chemist) was the world’s first zymologist, who connected yeast to the process of fermentation in year 1859. Pasteur gave the original definition of fermentation as respiration without the air. An anaerobic environment is not at all necessary for fermentation. For example, yeast cells prefer fermentation over the oxidative phosphorylation, even in the presence of the abundant oxygen; but for this fermentation process to carry on, sugars must be readily available for consumption.

For the process of fermentation, the sugars are the most commonly available substrates. The typical examples of the fermentation products are lactic acid, hydrogen and ethanol.

In fact, much more exotic compounds can also be produced by the process of fermentation, for example, acetone and butyric acid. Brewing industries produce ethanol by using the fermentation properties of yeast. All alcoholic drinks are produced by the microbial fermentation and this process also produces large quantities of carbon dioxide. Fermentation also occurs in the mammalian muscles during the periods of heavy exercise. When oxygen supply becomes limited, it leads to the production of lactic acid in the cells.

Energy source in anaerobic conditions
Almost all fermentation products possess chemical energy (i.e. they are not fully oxidized). But in the initial forms they are not at all useful, as they cannot be further metabolized without using oxygen or for the metabolizing they need other highly-oxidized electron acceptors. As a result, the production of ATP i.e. adenosine triphosphate, through fermentation is less efficient as compared to the production of ATPs through oxidative phosphorylation. But in fermentation, the pyruvate is fully oxidized into carbon dioxide. For the fermentation to carry on, the water must be warm. But it should not be hot, otherwise yeast cells will die.

Ethanol fermentation (conducted by some types of bacteria and yeast) breaks down the pyruvate into carbon dioxide and ethanol. It is very important in brewing, wine-making and bread-making. The fermentation process involves the simultaneous production of various products. But in a particular industry usually only one of the products is desired, for example—the alcohol is baked out in the bread-making and the carbon dioxide is released into the atmosphere in the alcohol production or it will be used for carbonating the beverage. Moreover, when the ferment possesses a high concentration of pectin, then extremely minute quantities of methanol can also be produced.

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