Ethanol fermentation

Ethanol fermentation, also called alcoholic fermentation, is a biological process which converts sugars such as glucose, fructose, and sucrose into cellular energy, producing ethanol and carbon dioxide as by-products. Because yeasts perform this conversion in the absence of oxygen, alcoholic fermentation is considered an anaerobic process. It also takes place in some species of fish (including goldfish and carp) where (along with lactic acid fermentation) it provides energy when oxygen is scarce.

Ethanol fermentation is the basis for alcoholic beverages, ethanol fuel and bread dough rising.

Biochemical process of fermentation of sucrose

The chemical equations below summarize the fermentation of sucrose (C12H22O11) into ethanol (C2H5OH). Alcoholic fermentation converts one mole of glucose into two moles of ethanol and two moles of carbon dioxide, producing two moles of ATP in the process.

C6H12O6 + 2 ADP + 2 Pi → 2 C2H5OH + 2 CO2 + 2 ATP

Sucrose is a sugar composed of glucose linked to fructose. In the first step of alcoholic fermentation, the enzyme invertase cleaves the glycosidic linkage between the glucose and fructose molecules.

C

12

H

22

O

11

+

H

2

O

→

Invertase

2

C

6

H

12

O

6

{\displaystyle {\ce {C12H22O11{}+H2O->[{\text{Invertase}}]2C6H12O6}}}

Next, each glucose molecule is broken down into two pyruvate molecules in a process known as glycolysis. Glycolysis is summarized by the equation:

C6H12O6 + 2 ADP + 2 Pi + 2 NAD+ → 2 CH3COCOO− + 2 ATP + 2 NADH + 2 H2O + 2 H+

CH3COCOO− is pyruvate, and Pi is inorganic phosphate.