Ethanol Production by Microbial Fermentation

 Ethanol and concentrated alcoholic drinks by fermentation- used since long for consumption.

 Microbial Fermentation in early days. But now, chemical synthesis

 In 1906 when the Industrial Alcohol Act was passed, the production of industrial alcohol, ethanol, became commercially feasible on a large scale.

 There are various uses of alcohol such as, 

1. Ethanol is used as an organic solvent in many different products as paints, perfumes, markers inks, varnishes, soaps, and other products like explosives.

2. The most popular use of ethanol is as motor fuel and fuel additive (gasohol)- renewable source for environmentally friendly fuels.

4. Ethanol is used as a potent food preservative in homes.

5. Ethanol is used in making antiseptic soap and cosmetics as it is effective against bacteria, fungi, and many viruses, but is not much effective against bacterial spores.

6. Ethanol is routinely consumed in different forms around the world like beer, wine, gin, whisky, etc. Beer is the most popular ethanol beverage in the world.

7. Ethanol plays an important role in making drugs and pharmaceuticals.

8. Ethanol is used in the preparation of essences and flavorings

9. Ethanol is used as the fluid in thermometers.

10. Ethanol is used in preserving biological specimens.

 Microbial Fermentation 

• Ethanol fermentation is a biological process in which sugars are utilized to produce ethanol and carbon dioxide as metabolic waste products.
• This process is carried out by yeast cells that converts glucose to CO₂ and alcohol.
• C₆H₁₂O₆ (glucose) → 2 C₂H₅OH (ethanol) + 2 CO₂ (carbon dioxide)
• Before fermentation, one glucose molecule is converted into two pyruvate molecules by glycolysis. 

• Under aerobic condition, some species of yeast (e.g., Kluyveromyces spp.) will oxidize pyruvate completely to carbon dioxide and water which is termed as cellular respiration.
• These species of yeast will produce ethanol only under anaerobic condition.
• So ethanol fermentation is classified as anaerobic process.
• However, many yeasts such as Saccharomyces cerevisiae (baker's yeast), Schizosaccharomyces pombe (fission yeast) will produce ethanol even under aerobic conditions
  
  
• Microorganisms

Many yeasts and bacteria such as Zymomonas mobilis are suitable for ethanol production. But, all yeasts are not suitable for brewing. Choice of yeast for the alcohol production depends upon the composition of the medium, particularly the type of carbohydrate used in the medium.

.

Raw materials	Fermentation Strain
Starch and sugar	Saccharomyces cerevisiae
Lactose of whey	Candida pseudotropicalis
Sulfur waste liquor	Candida utilis

 Selected strain should 

ü  grow rapidly.

ü  tolerate high concentrations of sugar.

ü  be able to produce abundant amounts of alcohol

ü  be resistant to the produced high concentrations of alcohol. 

Ethanol Fermentation

 Three stages

1. Media Preparation
2. Fermentation
3. Product harvesting/Distillation

                                   (contd)

References

Principles of Fermentation Technology: ( Peter F. Stanbury, Allan Whitaker )

Industrial Microbiology: (By Casida L. E.New Age international (P) ltd publications)

A Text Book of Industrial Microbiology: (2nd edition By Wulf Crueger & Anneliese Crueger)