Question

How is ethanol produced by fermentation?
A. Using anaerobic conditions at 30⁰C
B. Using anaerobic conditions at 450⁰C
C. Using steam at 30⁰C
D. Using steam at 450⁰C

Answer 1

Hint: Here, we need to recall fermentation and conditions involved in ethanol production. Fermentation: The chemical breakdown of a substance by bacteria, yeasts, or other microorganisms, typically involving effervescence and the giving off of heat is called fermentation.

 Complete step by step answer:
Ethanol or ethyl alcohol can be prepared on a commercial scale by the fermentation of sugar (present in molasses and grapes or rice, barley, maize etc.). The reactions taking place are catalysed by certain enzymes and in yeast. In the making of wine, grapes are the source of both sugar and yeast which brings about fermentation. When grapes are crushed, sugar and enzyme interact and the fermentation process starts. Fermentation takes place under anaerobic conditions i.e., in the absence of air at a temperature 30- 35⁰C. Carbon dioxide is evolved during the reaction with brisk effervescence- As a result, it seems as if the solution is boiling but actually it is not. The chemical reactions involved in process of fermentation are as follows:
Fermentation of sugar (sucrose):
\[{C_{12}}{H_{22}}{O_{11}}{\text{ + }}{{\text{H}}_2}O{\text{ }}\xrightarrow{{Invertase}}{\text{ }}{{\text{C}}_6}{H_{12}}{O_6}{\text{ + }}{{\text{C}}_6}{H_{12}}{O_6}\]
Sucrose Glucose Fructose
${{\text{C}}_6}{H_{12}}{O_6}{\text{ }}\xrightarrow{{Zymase}}{\text{ 2}}{{\text{C}}_2}{H_5}OH{\text{ + 2C}}{{\text{O}}_2}$\[\]
                  Ethanol
Fermentation of starch: Instead of sugar or grapes, the alcoholic fermentation can also be carried with barleys, potatoes, corn etc. which contains starch in them with general formula$(C6H10O5)n$. Unlike sucrose, starch has no taste. Its fermentation proceeds as follows:
${{\text{(}}{{\text{C}}_6}{H_{10}}{O_5})_n}{\text{ + n}}{{\text{H}}_2}O{\text{ }}\xrightarrow{{Diastase}}{\text{ n}}{{\text{C}}_{12}}{H_{22}}{O_{11}}$ (Maltose) , ${{\text{C}}_{12}}{H_{22}}{O_{11}}{\text{ + }}{{\text{H}}_2}O{\text{ }}\xrightarrow{{Maltase}}{\text{ 2}}{{\text{C}}_6}{H_{12}}{O_6}$

Hence, correct answer is (A)

Note:
The action of enzyme zymase causing the conversion of monosaccharide (${{\text{C}}_6}{H_{12}}{O_6}$) to ethyl alcohol is inhibited once the percentage of alcohol exceeds 14 percent. It is therefore desirable to carry alcoholic fermentation in dilute solution. Alcoholic fermentation must be carried in the absence of air. In case of air or oxygen vessels, ethanol is oxidised to ethanoic acid which can spoil the taste of alcohol.