Production of Ethanol by Fermentation

Alcohol, chemically ethanol (C2H5OH) has been produced by fermentation for thousands of years.

Microbes used:
Certain yeasts and bacteria are employed for alcohol fermentation, the type of the organism chosen mostly depends on the nature of substrate used.In yeast Sacchromyces cervisea is widely used and in bacteria Zymomonas mobilis is most frequently used for alcohol fermentation.

Raw Materials used for Alcohol Fermentation
There are large number of raw materials which can serve as substrate for alcohol fermentation. They are broadly categorized as

1. Sugary Raw Materials
2. Starchy Raw Materials
3. Cellulosic Raw Materials

Sugary raw materials includes Molases, whey, glucose, sucrose, etc.
Starchy raw materials includes Wheat, Rice, Maize, Potato.
Cellulosic raw materials includes Wood, agricultural wastes, etc.

Pre-Treatment
Most of the raw materials of alcohol fermentation requires some degree of pretreatment. The actual process depends on the chemical composition of the raw materials.
Sugary raw materials require mild ot no pretreatment while cellulosic raw material need extensive pretreatment. This is because cellulosic substance have to be subjected to acidic or enzyme hydrolysis to release monosaccharide units that are needed for alcohol production.

Biosynthesis of Ethanol

Glucose gets broken down to pyruvate by glycolysis under anaerobic conditions (in the absence of oxygen), pyruvate is converted to acetaldehyde by the enzyme pyruvate decarboxylase. Acetaldehyde is then reduced by alcohol dehydrogenase to form ethanol.

Regulation of Synthesis
Ethanol at high concentration in the medium inhibits its own biosynthesis, this is particularly observed when yeasts are fermentation organisms. it is generally seen that the growth of yeast ceases at 5% ethanol concentration. zymomonas mobilis can tolerate even higher alcohol concentration.

Production Process of Ethanol