How does fermentation work?

Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the process in which glucose is broken down anaerobically.

The process of fermentation is complex and involves several stages. Here's a simplified explanation of how fermentation works:

1. Glycolysis: The first stage of fermentation is glycolysis, which occurs in the cytoplasm of the cell. During glycolysis, one molecule of glucose is broken down into two molecules of pyruvate, along with a small amount of ATP (adenosine triphosphate) and NADH (nicotinamide adenine dinucleotide).

2. Pyruvate Decarboxylation: Pyruvate, produced during glycolysis, undergoes a chemical reaction called pyruvate decarboxylation. This reaction removes a carbon atom from pyruvate in the form of carbon dioxide (CO2), resulting in the production of acetaldehyde (in the case of ethanol fermentation) or acetyl-CoA (in the case of lactic acid fermentation).

3. Reduction: In the next step, the acetaldehyde or acetyl-CoA is reduced to form the final product of fermentation. In ethanol fermentation (performed by yeast), acetaldehyde is reduced to ethanol using NADH as an electron donor. In lactic acid fermentation (performed by some bacteria), acetyl-CoA is reduced to lactic acid using NADH as an electron donor.

4. Regeneration of NAD+: During the reduction step, NADH is utilized as an electron donor. To maintain the cellular balance, NADH must be regenerated back to NAD+ to keep the fermentation process going. This regeneration is achieved through various mechanisms, such as transferring electrons to an electron transport chain or using other metabolic pathways.

Overall, fermentation enables cells to generate ATP and produce specific end products (such as ethanol or lactic acid) without requiring oxygen. It plays a crucial role in various industries, including food production (e.g., brewing and yogurt making), beverage production, and biotechnology.