Lactic Acid Fermentation


This illustration shows that during glycolysis, glucose is broken down into two pyruvate molecules and, in the process, two N A D H are formed from N A D superscript plus sign baseline. During lactic acid fermentation, the two pyruvate molecules are converted into lactate, and N A D H is recycled back into N A D superscript plus sign baseline.
Lactic acid fermentation is common in muscle cells that have run out of oxygen. Source: OpenStax Biology 2e

OpenStax Biology 2e

The fermentation method used by animals and certain bacteria, such as those in yogurt, is lactic acid fermentation. This type of fermentation is used routinely in mammalian red blood cells, which do not have mitochondria, and in skeletal muscle that has an insufficient oxygen supply to allow aerobic respiration to continue (that is, in muscles used to the point of fatigue). In muscles, lactic acid accumulation must be removed by the blood circulation, and when the lactic acid loses a hydrogen, the resulting lactate is brought to the liver for further metabolism. The chemical reactions of lactic acid fermentation are the following:

The enzyme used in this reaction is lactate dehydrogenase (LDH). The reaction can proceed in either direction, but the reaction from left to right is inhibited by acidic conditions. Such lactic acid accumulation was once believed to cause muscle stiffness, fatigue, and soreness, although more recent research disputes this hypothesis. Once the lactic acid has been removed from the muscle and circulated to the liver, it can be reconverted into pyruvic acid and further catabolized for energy.


Clark, M., Douglas, M., Choi, J. Biology 2e. Houston, Texas: OpenStax. Access for free at:


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