Alcoholic Fermentation Yeasts and a few other microorganisms use alcoholic fermentation, which produces ethyl alcohol and carbon dioxide. A summary of alcoholic fermentation after glycolysis is

Alcoholic fermentation is used to produce alcoholic beverages. It is also the process that causes bread dough to rise. When yeast cells in the dough run out of oxygen, the dough begins to ferment, giving off tiny bubbles of carbon dioxide. These bubbles form the air spaces you see in a slice of bread. The small amount of alcohol produced in the dough evaporates when the bread is baked.

Lactic Acid Fermentation Most organisms carry out fermentation using a chemical reaction that converts pyruvic acid to lactic acid. Unlike alcoholic fermentation, lactic acid fermentation does not give off carbon dioxide. However, like alcoholic fermentation, lactic acid fermentation also regenerates NAD⁺ so that glycolysis can continue. Lactic acid fermentation after glycolysis can be summarized as

Certain bacteria that produce lactic acid as a waste product during fermentation are important to industry. For example, prokaryotes are used in the production of a wide variety of foods and beverages—such as cheese, yogurt, buttermilk, and sour cream—to which the acid contributes the familiar sour taste. Pickles, sauerkraut, and kimchi are also produced using lactic acid fermentation.

Humans are lactic acid fermenters. During brief periods without oxygen, many of the cells in our bodies are capable of producing ATP by lactic acid fermentation. The cells best adapted to doing that, however, are muscle cells, which often need very large supplies of ATP for rapid bursts of activity.

FIGURE 9–8 Fermentation In alcoholic fermentation, pyruvic acid produced by glycolysis is converted into alcohol and carbon dioxide. Lactic acid fermentation converts the pyruvic acid to lactic acid. Compare and Contrast What reactants and products do the two types of fermentation have in common?

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