Fermentation is a significant chemical process that occurs in our bodies. It is a way to get energy without oxygen, which is why it is called anaerobic, a term that means "occurring in the absence of free oxygen".
Fermentation occurs in the cytoplasm, a liquid that fills the cell. This liquid is made of water, salts, and various other molecules. Glucose and two ATP (cellular energy) units are consumed by the glycolysis, and the glucose is turned into four ATP units and two NADH.
There are two types of fermentation, alcoholic fermentation, and lactic acid fermentation. These types of fermentation produce the same amounts of ATP and NADH, but they also produce two different compounds, ethyl alcohol and lactic acid. In one cycle, alcoholic fermentation produces two units of ethyl alcohol and the lactic acid fermentation produces two units of lactic acid.
This type of producing energy takes place when our bodies need. When we don't have enough oxygen for aerobic respiration, our cells switch to anaerobic respiration and lactic acid builds up in our muscles, causing cramps.
Alcoholic fermentation is how wine and beer are made. However, aerobic respiration is more efficient than this kind of cellular respiration because it produces 36 ATP per cycle instead of four.