What is alcoholic fermentation

The microbial breakdown of carbohydrates takes place under anaerobic (oxygen-free) conditions via the fermentation process. Microorganisms constantly need new energy to maintain and divide cells. By utilizing saccharides (carbohydrates), the universal energy carrier ATP can be obtained through various reactions. If the cell has enough oxygen molecules in its environment, two effective processes take place with the citric acid cycle and the respiratory chain. If, however, there is a lack of oxygen, the cells cannot generate energy through these processes. Fermentation can still be used to produce ATP.

For 8,000 years, humans have made use of the breakdown processes of yeast. Beer and wine are ultimately the product of fermented carbohydrates like barley, wheat, or (in the case of wine) grapes. The fermentation process produces ethanol, better known as alcohol, as a by-product. For the yeast, however, ethanol is only a metabolic end product, i.e. it is useless for its own metabolism, which is why the yeast cells release it to the outside.
Ethanol also acts as a cell poison. From a concentration of approx. 20%, the yeast cells die, so high-proof alcoholic beverages can only be obtained through additional distillation.

The production of energy under anerobic conditions has far-reaching consequences for the cells. Only 2 ATP molecules are produced from one glucose molecule. For comparison: aerobic respiration produces 38 ATP. The yeast cells inevitably slow down their reproduction in an oxygen-free environment.