Manufacture of Alcohol

A primary industrial alcohol is ethanol, or ethyl alcohol (C2H5OH). Alcoholic fermentation is one of the oldest, best known and most important of industrial fermentations. In this process, ethyl alcohol is produced from carbohydrate materials (such as sugars) by yeasts. The process is extracellular. The overall biochemical change accomplished by the yeast is represented by the following equation.


This ability of the yeasts to convert sugars to alcohol and other end products of value has been exploited a great deal by brewers, bakers, distillers, wine makers, chemical manufacturers, vinegar manufacturers, etc.

(A) A Tubular Tower Fermenter
(B) Flow Chart of alcoholic fermentation

Manufacture of ethyl alcohol

1. Raw materials used : Molasses are one of the commonest raw materials used in the manufacture of alcohol. This is because they are cheap and readily available in large quantities.

2. Micro-organism used : Selected strains of the yeast Saccharomyces cerevisiae are commonly employed for fermentation. This is because (a) they grow vigorously, (b) they have high tolerance for alcohol and (c) they have a high capacity for producing a large yield of alcohol.

Steps involved in the process

It is a large scale biotechnological process requiring large scale tubular tower fermenters (bio-reacters) and involves the following steps.

a. Preparation of the medium : Water is added to the molasses to bring down the sugar concentration to the desired level (usually 30 to 40 percent). A measured quantity of acid is then added so as to adjust the pH on the acidic side.

b. Addition of yeast : After adjusting the desired temperature, a yeast ‘starter’ is allowed to be mixed thoroughly with the molasses ‘mash’ in the fermentation tank.

c. Fermentation : Fermentation by the yeast process starts and soon becomes vigorous. A large quantity of carbon dioxide is evolved during the process. The gas (by-product of the alcohol industry) is collected, purified and used in various other industries.

d. Separation of ethyl alcohol : Alcoholic fermentation is completed in about 48 hours. The fermented medium contains alcohol as well as other volatile constituents and unused constituents of the molasses. Therefore, separation of ethyl alcohol from other impurities is necessary. This is done by distillation.

e. Purification : Finally, alcohol is purified with the help of rectifying columns and stored in bonded warehouses.


Ethyl alcohol is also formed as one of the products of fermentation during the manufacture of alcoholic beverages such as beer, wine, whisky, rum and gin.


Different types of alcoholic beverages are obtained by making use of the fermentation activity of different strains of yeast Saccharomyces as shown in the following table.

Various products of alcoholic fermentation

Beverage
Substrate
Micro-organism (Saccharomyces)
Species/Strains
Alcohol %
01. Wine
Grape juice
S. ellipsoideus
10-12%
02. Beer
Cereals
S. cerevisae
4-8%
03. Rum
Black strap molasses
-
-
04. Whiskey
Cereals
-
51-59%
05. Sake
Starch (rice)
Aspergillus oryzae,
Lactobacillus and S. cerevisae

16%
06. Champagne
Grape juice
-
12-13%
07. Brandy
Wine
-
43-57%

Reference :
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