What is fermentation?

Fermentation is a chemical process where molecules like glucose are broken down without oxygen. This process, used for millennia in making wine and beer, creates frothing from carbon dioxide release. Louis Pasteur defined fermentation as changes from yeasts and microbes growing without air, noting that ethyl alcohol and carbon dioxide aren't the only results. Today, fermentation means the enzyme-driven, energy-releasing pathway in cells that anaerobically breaks down molecules such as glucose. Enzymes for this process are in the soluble part of the cytoplasm. The reactions that create ATP and pyruvate are shared in sugar transformation across muscles, yeasts, some bacteria, and plants.

How does fermentation differ from regular respiration?

Fermentation and cellular respiration are both processes that organisms use to derive energy from foodstuff molecules. Fermentation is an anaerobic process where molecules like glucose are broken down without oxygen. In contrast, respiration uses oxygen to break down foodstuff molecules into carbon dioxide and water. During fermentation, an organic compound is broken down into smaller organic molecules, which accept electrons released during the breakdown of the energy source. This process yields only two molecules of ATP per glucose molecule. Respiration, on the other hand, transfers electrons from sugar molecules to an inorganic molecule, such as oxygen, yielding a maximum of 38 ATP molecules per glucose molecule.

What are the main types of fermentation?

Fermentation is a chemical process that breaks down molecules like glucose anaerobically. Industrial fermentation uses microorganisms under specific conditions to produce various products. Main types of fermentation: * Alcoholic fermentation Yeast fermentation of sugars produces alcohol, carbon dioxide, and glycerol. The brewing industry has used this process for millennia to produce ethanol, an important biofuel. * Acetic acid fermentation Specific bacteria oxidize alcohol to produce acetic acid, essential in creating vinegar. This process is also known as acetification. * Lactic acid fermentation Certain bacteria produce lactic acid through carbohydrate fermentation, which is vital for manufacturing pickles, yogurt, and cheese. * Other fermentation processes Various Clostridium species create organic compounds like acetone, isopropanol, and butyric acid on an industrial scale.

How is yeast involved in fermentation?

Yeast plays a vital role in fermentation by converting sugars into ethanol and carbon dioxide. Saccharomyces cerevisiae strains are especially important in the production of beer, wine, and bread. In brewing and winemaking, yeast ferments sugars from malted grains or fruits, yielding alcoholic beverages. The carbon dioxide produced contributes to the effervescence of beer and sparkling wine. In baking, carbon dioxide released during fermentation causes dough to rise, while the ethanol evaporates during baking. Sourdough starters, used in bread making, contain S. cerevisiae and wild yeast strains, along with lactic acid bacteria.

What are some everyday products made using fermentation?

Fermentation is a chemical process that breaks down molecules like glucose anaerobically. This process has been used for thousands of years in the creation of various products. Everyday products made using fermentation:

Why is fermentation important for living things and industry?

Fermentation is a chemical process that breaks down molecules like glucose anaerobically. For living organisms, fermentation provides energy. Bacteria use fermentation and respiration to metabolize sugars, with fermentation being an anaerobic process that breaks down organic compounds into smaller molecules, yielding ATP. Industrially, fermentation produces various products, including alcohol, glycerol, carbon dioxide, lactic acid, and acetic acid. Yeast fermentation of sugars yields alcohol, glycerol, and carbon dioxide. Bacterial fermentation produces butyl alcohol, acetone, lactic acid, monosodium glutamate, and acetic acid. Mold fermentation produces citric acid, gluconic acid, and small amounts of antibiotics and vitamins. The brewing industry relies on yeast to produce ethanol, and specific bacteria oxidize alcohol to acetic acid in vinegar production.

fermentation

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An ethanol production plant with large metal silos and white smoke rising from a stack, set behind a field of dry corn in South Dakota.

Diagram showing the steps of glycolysis, beginning with glucose and ATP, progressing through intermediates like glucose 6-phosphate and fructose 6-phosphate, and ending with the production of pyruvate, ATP, and NADH. A detailed inset highlights the enzymatic reactions and energy transfers from glyceraldehyde 3-phosphate to pyruvate.

Illustration of a flame overlaid on a vintage distillery, with drawings of wheat, sugar, and bubbles around it.

Figure 1: A schematic representation of the biogeochemical cycle of carbon.

fermentation and distillation process for producing whiskey

Illustrated diagram of the carbon cycle showing how carbon moves as carbon dioxide through the atmosphere, water, living organisms, rocks, and soil. It depicts processes like photosynthesis, respiration, sedimentation, volcanic activity, fossil fuel use, and carbon sequestration, with arrows indicating the flow between air, water, plants, animals, rocks, and industrial sources.

Behind the scenes: How Samuel Adams beer is made

A man wearing a hairnet and gloves pours a dark liquid into a lighter-colored vat.

The process of making sparkling wine explained

Quick Facts

Key People:: Louis Pasteur; Hans von Euler-Chelpin; Sir Arthur Harden; Eduard Buchner

Related Topics:: cap; bottle fermentation; bottom fermentation; malolactic fermentation; tank fermentation

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fermentation

chemical reaction

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Top Questions

What is fermentation?
Fermentation is a chemical process where molecules like glucose are broken down without oxygen. This process, used for millennia in making wine and beer, creates frothing from carbon dioxide release. Louis Pasteur defined fermentation as changes from yeasts and microbes growing without air, noting that ethyl alcohol and carbon dioxide aren't the only results.

Today, fermentation means the enzyme-driven, energy-releasing pathway in cells that anaerobically breaks down molecules such as glucose. Enzymes for this process are in the soluble part of the cytoplasm. The reactions that create ATP and pyruvate are shared in sugar transformation across muscles, yeasts, some bacteria, and plants.
2 Britannica Sources
1. fermentation
2. bacteria: Bacteria in industry
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How does fermentation differ from regular respiration?
Fermentation and cellular respiration are both processes that organisms use to derive energy from foodstuff molecules. Fermentation is an anaerobic process where molecules like glucose are broken down without oxygen. In contrast, respiration uses oxygen to break down foodstuff molecules into carbon dioxide and water.

During fermentation, an organic compound is broken down into smaller organic molecules, which accept electrons released during the breakdown of the energy source. This process yields only two molecules of ATP per glucose molecule. Respiration, on the other hand, transfers electrons from sugar molecules to an inorganic molecule, such as oxygen, yielding a maximum of 38 ATP molecules per glucose molecule.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What are the main types of fermentation?
Fermentation is a chemical process that breaks down molecules like glucose anaerobically. Industrial fermentation uses microorganisms under specific conditions to produce various products.

Main types of fermentation:
* Alcoholic fermentation Yeast fermentation of sugars produces alcohol, carbon dioxide, and glycerol. The brewing industry has used this process for millennia to produce ethanol, an important biofuel.
* Acetic acid fermentation Specific bacteria oxidize alcohol to produce acetic acid, essential in creating vinegar. This process is also known as acetification.
* Lactic acid fermentation Certain bacteria produce lactic acid through carbohydrate fermentation, which is vital for manufacturing pickles, yogurt, and cheese.
* Other fermentation processes Various Clostridium species create organic compounds like acetone, isopropanol, and butyric acid on an industrial scale.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How is yeast involved in fermentation?
Yeast plays a vital role in fermentation by converting sugars into ethanol and carbon dioxide. Saccharomyces cerevisiae strains are especially important in the production of beer, wine, and bread.

In brewing and winemaking, yeast ferments sugars from malted grains or fruits, yielding alcoholic beverages. The carbon dioxide produced contributes to the effervescence of beer and sparkling wine. In baking, carbon dioxide released during fermentation causes dough to rise, while the ethanol evaporates during baking. Sourdough starters, used in bread making, contain S. cerevisiae and wild yeast strains, along with lactic acid bacteria.
4 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What are some everyday products made using fermentation?
Fermentation is a chemical process that breaks down molecules like glucose anaerobically. This process has been used for thousands of years in the creation of various products.

Everyday products made using fermentation:
- Leavened baked goods The baker's yeast, Saccharomyces cerevisiae, ferments sugars like glucose and produces carbon dioxide, which leavens the dough, and ethanol, which adds to the aroma.
- Alcoholic beverages Beer is made through the fermentation of sugars derived from malted grains, while wine results from the fermentation of fruits. Distilled spirits are made by fermenting a grain mash or fruit juice with yeast and then concentrating the alcohol through distillation.
- Kombucha This beverage is made of fermented green or black tea and contains a number of microorganisms, including a variety of yeasts and bacteria.
- Cultured dairy products Yogurt and sour cream are made through bacterial fermentation.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Why is fermentation important for living things and industry?
Fermentation is a chemical process that breaks down molecules like glucose anaerobically. For living organisms, fermentation provides energy. Bacteria use fermentation and respiration to metabolize sugars, with fermentation being an anaerobic process that breaks down organic compounds into smaller molecules, yielding ATP.

Industrially, fermentation produces various products, including alcohol, glycerol, carbon dioxide, lactic acid, and acetic acid. Yeast fermentation of sugars yields alcohol, glycerol, and carbon dioxide. Bacterial fermentation produces butyl alcohol, acetone, lactic acid, monosodium glutamate, and acetic acid. Mold fermentation produces citric acid, gluconic acid, and small amounts of antibiotics and vitamins. The brewing industry relies on yeast to produce ethanol, and specific bacteria oxidize alcohol to acetic acid in vinegar production.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

fermentation, chemical process by which molecules such as glucose are broken down anaerobically. More broadly, fermentation is the foaming that occurs during the manufacture of wine and beer, a process at least 10,000 years old. The frothing results from the evolution of carbon dioxide gas, though this was not recognized until the 17th century. French chemist and microbiologist Louis Pasteur in the 19th century used the term fermentation in a narrow sense to describe the changes brought about by yeasts and other microorganisms growing in the absence of air (anaerobically); he also recognized that ethyl alcohol and carbon dioxide are not the only products of fermentation.

Anaerobic breakdown of molecules

In the 1920s it was discovered that, in the absence of air, extracts of muscle catalyze the formation of lactate from glucose and that the same intermediate compounds formed in the fermentation of grain are produced by muscle. An important generalization thus emerged: that fermentation reactions are not peculiar to the action of yeast but also occur in many other instances of glucose utilization.

Glycolysis, the breakdown of sugar, was originally defined about 1930 as the metabolism of sugar into lactate. It can be further defined as that form of fermentation, characteristic of cells in general, in which the six-carbon sugar glucose is broken down into two molecules of the three-carbon organic acid, pyruvic acid (the nonionized form of pyruvate), coupled with the transfer of chemical energy to the synthesis of adenosine triphosphate (ATP). The pyruvate may then be oxidized, in the presence of oxygen, through the tricarboxylic acid cycle, or in the absence of oxygen, be reduced to lactic acid, alcohol, or other products. The sequence from glucose to pyruvate is often called the Embden–Meyerhof pathway, named after two German biochemists who in the late 1920s and ’30s postulated and analyzed experimentally the critical steps in that series of reactions.

Double exposure of science laboratory test tubes with bokeh and chemical reaction

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Types of Chemical Reactions

The term fermentation now denotes the enzyme-catalyzed, energy-yielding pathway in cells involving the anaerobic breakdown of molecules such as glucose. In most cells the enzymes occur in the soluble portion of the cytoplasm. The reactions leading to the formation of ATP and pyruvate thus are common to sugar transformation in muscle, yeasts, some bacteria, and plants.

Industrial fermentation

Industrial fermentation processes begin with suitable microorganisms and specified conditions, such as careful adjustment of nutrient concentration. The products are of many types: alcohol, glycerol, and carbon dioxide from yeast fermentation of various sugars; butyl alcohol, acetone, lactic acid, monosodium glutamate, and acetic acid from various bacteria; and citric acid, gluconic acid, and small amounts of antibiotics, vitamin B₁₂, and riboflavin (vitamin B₂) from mold fermentation. Ethyl alcohol produced via the fermentation of starch or sugar is an important source of liquid biofuel.

The Editors of Encyclopaedia Britannica

This article was most recently revised and updated by Meg Matthias.

fermentation

Anaerobic breakdown of molecules

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Industrial fermentation