Production of alcohol by yeast and bacteria

1. Production of alcohol:

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3. Introduction:
 Alcohol chemically ethanol (C2H5OH) produced by fermentation.
 Brazil was the first country to produce ethanol in large scale by
yeast fermentation utilizing sugarcane.
 Alcohol used as motor fuel is referred to as green petrol.


4. History:
 For centuries alcohol has always played an important, and
sometimes decisive role in warfare.
 Back in the days of Ancient Greece and later Ancient Rome it
was quite normal to give soldiers a daily ration of alcohol.

5. Microorganisms used for alcohol production:
 Yeast: Saccharomyces cerevisiae (Sugar)
 Bacteria: Zymomonas mobilis (Starch)
 The type of organism chosen mostly depends on the nature of
the substrate.

6. Raw Materials:
 There are large number of raw materials that can serve as
substrates for alcohol fermentation.
 Sugary materials: Glucose, Sucrose, Molasses.
 Starch materials: Wheat, rice, Maize and potato.
 Cellulose materials: Wood and agricultural wastages.

7. Pre-treatment of raw materials:
 The sugary materials not require pre-treatment.
 While the cellulosic materials need extensive pre-treatment.
 The cellulose materials subjected to acidic or enzymatic hydrolysis
to release monosaccharide units.

8. Preparation of Nutrient solution or media:
 Molasses is used for fermentation, it is diluted with water and
sugar concentration maintained between 10-18% per 100 ml.
 Ammonium salts like ammonium sulfate or phosphate are add
to the nutrient solution or media.
 The pH of the medium adjusted to 4-5 adding sulfuric or lactic
acid.

9. Preparation of inoculum:
 The selected microorganism isolated in pure form and cultured
in small size flask or fermenters.
 Under controlled condition the size of the inoculum increases
which can be used for inoculation.

10. Biosynthesis of ethanol:
 Glucose break down into Pyruvate. (Glycolysis)
 Under anaerobic conditions pyruvate converted in to
acetaldehyde by the enzyme pyruvate decarboxylase.
 Acetaldehyde form alcohol by the enzyme Alcohol
dehydrogenase.

11. pyruvate decarboxylas
Alcohol dehydrogenase.

12. Fermentation:
 Batch fermentation generally used now at most places continuous
fermentation is used.
 Because yield is very high when compare to batch fermentation.

13.  The ideal pH is 4.0-4.5.
 The initial temperature is 21-27 °C.
 The temperature raises during the fermentation up to 30 to 37°C.
 The fermentation process to be complete 2-3 days under these
conditions.

14. Glucose to alcohol conversion profile:
 One gram of glucose converted in to 0.511 grams of ethanol.
 It is estimated that for 100g pure glucose:
 48.5 g of ethanol
 46.5 gms of CO2 and
 1.3g of biomass is produced after fermentation yeast.

15. Recovery of ethanol:
 The cell mass is separated by centrifugation.
 Ethanol is purified by successive distillations.
 It is easy to obtain 95% ethanol concentration.

16. Beer Fermentation:

17.  It is generally prepared from malted barley but other starchy
grains, e.g..Wheat, maize, rice are also used as raw materials.
 Yeasts especially Saccharomyces cerevisiae are used in the
fermentation process.
Beer Fermentation:

18. Major steps are involved in the manufacture of beer:
Step: 1: Malting:
 The malt is prepared by first soaking the grains in water and
then allowing it to germinate at 17°C.
 After the germination is completed, the grains are dried at
65°C.

19. Mashing:
 After malting, the pure barley malt is mixed with other grains such
as corn, rye, wheat, etc.
 It is called ‘ground malt’.
 The ground malt mixed with warm water at about 70°C.
 .

20.  Mashing brings about partial hydrolysis resulting in the digestion
of starch and protein;
 The partially hydrolysed solution of mash is filtered and this
filtrate is called ‘beer wort’.
 Beer wort serves as a rich nutrient medium for the
microorganisms.

21. Fermentation: