Here is your short paragraph on Fermentation.
When the yeast cells grow in the sugarcane juice, toddy juice, or grape juice, then because of the activity of zymase enzyme the fermentation takes place.
The sugar decomposes producing alcohol and carbon dioxide. In the abundance supply of oxygen the alcohol is formed in less quantity. On the other hand when there is scarcity of oxygen the large quantity of alcohol is produced.
The conversion of sugars into alcohol is termed alcoholic fermentation. The alcohol forming yeasts that grow at the top of the fermenting liquid are known as ‘top yeasts’. The other yeasts which grow in the lower portions are known as ‘bottom yeasts’. Though yeasts grow in less supply of oxygen yet fermentation does not take place in total absence of oxygen and most of the yeasts are intermediate between aerobic and anaerobic types. During fermentation besides the production of alcohol and carbon dioxide other substances like glycerol, ethers, fatty acids, acetic acid and succinic acid are also produced in small quantities.
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The important fermenting yeasts are the wine yeast (Saccharomyces ellipsoides); the beer and bread yeasts (S. cerevisiae); the ginger beer yeast (5. piriformis)-, the same wine yeast of Japan (S. sake); African beer yeast (5. pmbe), etc.
Systematic Position G W. Martin (1961):
The yeasts are rich in enzymes and vitamins arid therefore, they make a valuable food and useful as medicine. The cubes or cakes with inactive starch as the base are made from the yeasts. Yeast tablets cure the stomach troubles. Certain pathogenic yeasts have also been reported.
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C6H12O6 + Zymase 2C2H5OH + 2CO2 + Zymase + Energy.