Fermentation

Fermentation is a biological process in which microorganisms break down sugars and other organic compounds to obtain energy without requiring oxygen, as in normal respiration. The products include substances such as ethanol, lactic acid, and carbon dioxide.

The term is also used in an industrial sense: food preparation and production methods in which bacteria, yeast, or fungi transform food, beverages, or chemical materials. Bread, yogurt, meat, beer, wine, and vinegar all depend on this process.

How it works

Initially, a microorganism breaks down sugar (usually glucose) through a process called glycolysis, which produces small amounts of energy stored in molecules called ATP. This process requires an electron carrier (NAD+) to be regenerated. In the absence of oxygen, the microorganism converts the products of glycolysis into something else—for example ethanol or lactic acid—so that NAD+ is restored and glycolysis can continue.

Common types

Alcoholic fermentation is carried out by yeast, particularly Saccharomyces cerevisiae; it produces ethanol and carbon dioxide, and forms the basis of beer, wine, and root beer production. Lactic acid fermentation is performed by lactic acid bacteria; it occurs in yogurt, meat, and preserved foods. There are also other types, such as acetic acid fermentation in vinegar (which requires oxygen for part of the process).

Uses

Fermentation is among the oldest food preservation techniques: the acids and alcohols produced reduce the growth of harmful microorganisms. It also changes the flavor and structure of food, and in some cases aids digestion. In modern industry, fermentation is used to produce medicines (such as certain antibiotics), enzymes, biofuel, and chemical compounds.

History

People used fermentation thousands of years before understanding its cause. In the nineteenth century, scientists—notably Louis Pasteur—showed that microorganisms were responsible for the process, disproving earlier theories that it was purely chemical. Subsequently, biochemistry explained the enzymes within cells that carry out the work.