Fermentation, originally, the foaming that occurs during the manufacture of and , a process at least 10,000 years old. That the frothing results from the evolution of gas was not recognized until the 17th century. 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 and carbon dioxide are not the only products of fermentation. In the 1920s it was discovered that extracts of catalyze, in the absence of air, the formation of lactate from and that the same intermediate compounds formed in the fermentation of grain are produced by . An important generalization thus emerged: that fermentation reactions are not peculiar to the action of but also occur in many other instances of utilization. Which means dissolution of sugar, was originally defined around 1930 as the 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 to the synthesis of (ATP). The pyruvate may then be oxidized, in the presence of oxygen, through the , or in the absence of oxygen, be reduced to , alcohol, or other products. The sequence from glucose to pyruvate is often called the Embden–Meyerhof pathway after two German biochemists who, in the late 1920s and 1930s, postulated and analyzed experimentally the critical steps in that series of reactions.

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