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What Is Fermentation & How Does it Differ From Glycolysis?

Fermentation and glycolysis are two major steps in producing energy. Glycolysis may exist without fermentation, because it is a prerequisite of the latter. Fermentation ensures the continuity of glycolysis in some situations. In its simplest definition, fermentation is an anaerobic cellular process in which foods are converted into simple compounds, which in turn produces chemical energy.

Cellular Respiration and Glycolysis
- There are two kinds of cellular respiration: aerobic (with oxygen) and anaerobic (without oxygen). In mammals, aerobic respiration is the primary means of obtaining energy from food. Cells store energy as potential energy in strong bonds of a compound molecule known as ̶0;adenosine triphosphate̶1; (ATP). Synthesis of ATP begins with glycolysis, which is the process of splitting glucose, a sugar obtained from food, into two 3-carbon molecules called pyruvate. For this to happen, glucose reacts with a chemical called NAD+ in a process called reduction-oxidation (redox) reaction, releasing and storing energy along the way.
Role of Fermentation in Energy Production
- Electrons released during redox reactions are ultimately taken up by oxygen to produce water. Without oxygen to receive the electrons, NADH (the reduced form of NAD+) is useless in redox reactions. The absence of oxygen does happen in some processes and this is where fermentation comes in. In fermentation, pyruvate reacts with NADH to regenerate NAD+, which can, again, participate in glycolysis to produce more ATP.
Physical Manifestation
- The cellular respiration of muscles can clearly describe fermentation. In this process, a byproduct called lactic acid is produced through the breakdown of pyruvate. When the oxygen supply cannot keep up with heavy or prolonged work, muscle cells switch to anaerobic respiration to obtain energy. It is the presence of lactic acid that makes the muscles sore during cramps and the morning after working out in the gym.
Other Uses
- Fermentation is commonly used in winemaking, brewing beer and treating tea leaves. It breaks down some unwanted chemicals and modifies other components to develop the flavor of the tea. It is also used in producing pharmaceutical citric acid. The fungus Aspergillus niger ferments a molasses substrate to form citrate.

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