Chemistry

 

Fermentation

Fermentation is the process by which complex organic compounds are split into simpler ones by "ferments" or enzymes. A number of important chemicals and antibiotics are produced by this process. The most familiar example is the fermentation of glucose into ethyl alcohol ("alcohol").

Alcoholic Fermentation

The original use of fermentation was to produce alcoholic drinks. The first alcoholic beverage is believed to be mead, made from fermented honey. Wine made from fruit or rice are other examples of early use.

Note: The basis for scientific understanding of this process, that is, that it depends on the presence of yeast, a micro-organism, was the work of Louis Pasteur (1822-1895). Other chemists determined that it is the enzymes released by yeast that carry out the actual fermentation.

Using Sugar and Starch

While cane sugar (sucrose) could be used as the starting point, in practice less expensive sources of sugar are used. For example, potato starch, grain, or black strap molasses are used. The steps in fermenting starch to alcohol are shown in the following table.

 

Enzyme	From	Action	Formula
diastase	Malt (germinating barley)	Hydrolysis of starch to maltose. Note: The temperature required for this reaction is about 50o C. (122o F.).	(C6H10O5)n + H2O ---> 2(C6H12O6)
maltase	Yeast	Hydrolysis of maltose to glucose. Note: This reaction is carried out at warm room temperature (about 27o C. or 81o F.).	C12H22O11 + H2O ---> 2(C6H12O6)
zymase	Yeast	Fermentation of glucose to ethyl alcohol and carbon dioxide. Note: This reaction is carried out at warm room temperature (about 27o C. or 81o F.). The process requires a few hours, after which the alcohol is recovered by distillation.	C6H12O6 ---> C2H5OH + 2CO2

Alcoholic Concentrations

Alcoholic concentration is expressed using the terms defined in the following table.

Term	Definition
100% proof	50% alcohol by volume
Alcohol	188 - 192 proof
Pure ethyl alcohol	190 proof
Absolute alcohol (water-free alcohol)	200 proof