Fermentation

Fermentation is the conversion of certain sugars, usually by microorganisms. The strict definition implies a transformation of sugar in the absence of oxygen.

Dough fermenting

Many things can be fermented. Generally, the product of fermentation is more digestible, has a longer shelf life, or produces a desirable molecule, such as alcohol in the case of alcoholic fermentation.

We owe much of our understanding of fermentation to Louis Pasteur.

Yeast

Baker's yeast is responsible for several types of fermentation that humans enjoy. The scientific name for yeast is Saccharomyces cerevisiae. It is a single-celled, microscopic fungus. Yeast is added to bread dough to make it rise and make the bread lighter, as it traps carbon dioxide. The same yeast can be used to produce beer, making the resulting beverage alcoholic. This is a way to preserve grain by altering it.

Types of fermentation

Lactic fermentation

This fermentation occurs in many organisms, but also in our muscles. When we exert ourselves—for example, during a fast run—and there isn't enough oxygen in the muscle, this fermentation takes place. In this case, the muscle uses this process because it needs the energy from a sugar called glucose. Under normal circumstances, glucose is used in the presence of oxygen, which provides a lot of energy to the cells. When energy is needed urgently and the muscle lacks sufficient oxygen, it ferments the glucose, producing lactic acid. This acid is responsible for cramp in the muscles after intense exercise, but not for side stitches.

Alcoholic fermentation

Some organisms are capable of using sugars to produce ethyl alcohol. For this to happen, there must be plenty of sugar and no oxygen: this is why wine is made in barrels. Baker's yeast is also called "brewer's yeast" because it can produce alcohol.

Why fermentation?

Fermentation is a way for living organisms to produce the energy they need to survive, even when there is little or no oxygen. From a chemist's perspective, fermentation is an "incomplete oxidation". Most cells in our body are capable of fermentation to some degree. There are even types of yeast that do not need oxygen at all to survive: they do not breathe!

		Did you know?
	The human body is also capable of fermentation!
Muscle cells are the only cells in the human body that are capable not only of respiring, like the rest of the body, but also of fermenting when there is no, or not enough, oxygen available for respiration. This happens particularly during intense, rapid physical exercise: the breathing rate increases to supply the body with more oxygen, which the muscles need. But sometimes, when the exercise is very fast, the oxygen doesn't have time to reach the muscles, and the muscle cells must find another way to produce energy: they ferment. Like the bacteria found, for example, in yogurt, muscle cells are able to convert sugar into lactic acid and energy when there isn’t enough oxygen. This allows them to "hold out" until the body adapts and oxygen arrives. However, this poses a problem: the acid produced in this way prevents the muscle from functioning normally, and if there is too much of it, it will cause a very painful muscle contraction known as a cramp. To avoid cramps, it is therefore important to breathe properly during physical exercise.

Some fermented products

• beer (alcoholic fermentation)
• yogurts (lactic fermentation)
• sauerkraut (lactic fermentation)
• vinegar (acetic fermentation)
• shrimp paste
• Kombucha (acetic fermentation)

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Source : This page has been adapted from the page « Fermentation » on Vikidia in French. (Authors list)