Write a note on Fermentation.

Ans. Fermentation is the anaerobic decomposition of sugars, starches and other carbohydrates by the enzymes action of micro organisms. The power of micro organisms especially the yeast, to bring about fermentation is of great industrial value especially in alcohol preparation. The fermentative properties of yeast are used in beer and baking industries.

The various species of bacteria also have the capacity of fermenting particular carbohydrates. Certain species of bacteria can decompose cellulose, others can decompose some polysaccharides such as insulin, dextrin and starch. Few species can attack on the saccharides such as sucrose, maltose and lactose (Milk sugar).

As a result of fermentation by bacteria various organic acids are formed and often gases are also produced. The lactic acid bacteria produces lactic acid causing the souring milk.

Formation of acetic acid by acetobactor, butyric acid by clostridium butyrium are also common examples of bacterial fermentation.

Importance: The fermentative processes (Production of acids and alcohol, etc.) are of great importance in household and in industries. Retting of jute, tobacco curling, tanning of leather are other common examples of the industrial uses of fermentative processes brought about by the microbes.

(i) Retting of Jute: It is done by immersing the stalks of Jute in pond water, where tissues particularly their pectic substances swell up by absorbing the water.

(ii) Tobacco Curling Tobacco leaves are curled and fermented to improve the colour, texture and aroma of finished products. Certain bacteria such as Bacillus megatherium, Bacillus subtilis, etc. play a vital role in fermentation of tobacco leaves.

(iii) Ethyl alcohol: This is produced by fermentable carbohydrates by the enzymatic activity of yeast such as Saccharomyces cerevisiae.

(iv) Beer: This is prepared by enzymatic action of Aspergillus oryzae on starch.

Starch → Sugar → Alcohol

(v) Wine: This is prepared by the action of yeast on the fruit juices.

(vi) Rum: Rum is produced by the fermentation of molasses with the help of Saccharomyces cerevisiae.

(vii) Vinegar : This is produced by the conversion of sugary material to alcohol anaerobically through saccharomyces ellipsoideus. So formed alcohol is converted into acetic acid aerobically through some species of Acetobacter.

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