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{{sci-outline}}{[biology}} Fermentation is a biological process undergone by many different organisms, but most notably in yeastWikipedia, bacteria, and human muscle cells. It occurs when any of these attempt cellular respirationWikipedia but lack the oxygen to complete the entire process, and the results depend on the organism.

In yeast[edit]

Yeast are famous for fermentation, mostly because it makes beer and bread. Fermentation and cellular respiration are quite a bit more complicated than this, but the basic steps are as follows:

  1. Yeast is placed in a location without oxygen (the dough in the case of bread and an airtight bottle if making beer).
  2. Since it cannot undergo cellular respiration without oxygen, the yeast instead produces the energy it needs to survive through ethanol fermentation. This is when glucose (or another carbohydrate) is converted into two moles of ATP, considerably less than the amount produced during cellular respiration, and produces 2 moles of ethanol and 2 of carbon dioxide as a byproduct.