Fermentation Process of Alcohol Production

BACKGROUND

Alcohol

Alcohols are vital industrially and commercially. Commercial alcohol includes Methanol, Ethanol, Isopropanol, and Ethylene Glycol. Ethanol is used as a solvent, as a fuel additive, in medicines, lotions. Ethanol is generally referred as common alcohol.¹ 

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Ethanol is produced by fermentation of sugars. Fermentation is a chemical breakdown of a substance by bacteria, yeasts or other microorganisms. The fermentation of carbohydrates into alcohol is one of the oldest processes of fermentation.

The fermentation starts by mixing source of sugar, yeast, water and then allowing yeast to act in oxygen free environment. This anaerobic environment forces the yeast to shut down the burning of sugar & allows them to ferment alcohol.

So the basic objective of the test is to carry out the production of Ethanol by the process of fermentation.

REQUIREMENTS

Chemicals:     Corn steep glucose, Glucose

Apparatus:     Fermenter, Centrifuge, Flask

PROCEDURE

Process of Alcohol Production

Commercially fermentation is the initial step for production of wine, beer, cider.

Ethanol fermentation

Ethanol fermentation is a biological process that converts sugars such as glucose / sucrose into cellular energy producing ethanol and CO₂ as by-products.² Fermentation is the process where yeasts breakdown into alcohol and carbon dioxide. Yeasts perform the conversion in the absence of oxygen because of which alcoholic fermentation is considered as an anaerobic process.³ 

For fermentation process yeast such as Saccharomyces cerevisae is used.⁴ Raw material that can be served as substrate is Glucose/ sucrose.⁵ The raw materials at first requires mild/no pre-treatment before fermentation.⁶

Media preparation

After the selection of the desired yeast (Saccharomyces cerevisae) and its isolation in pure form, the inoculum is prepared under aseptic conditions. The yeast is first cultured in flask to increase the size of the inoculums as it will be suitable for inoculation.

Fermentation

For fermentation, continuous fermentation is used. For continuous fermentation, the growth of microbes is maintained in the Fermenter for a long period of time; in the meantime the media is added at regular intervals.⁷ Temperature & pH is maintained at 21-26^oC & 4.0-4.5 respectively.

The product from the Fermenter is collected again & again to avoid overflow, but the fermentation never stops & thus continues for a long period of time with addition of nutrients and harvesting the metabolites at regular intervals. Ethanol gets evaporated at temperature above 27^oC.

Firstly aeration is required for good growth of organisms; later anaerobic condition is created by withdrawal of oxygen coupled with the production of carbon dioxide. Then as the fermentation is complete, the fermentation broth contains ethanol in the range of 6-9% in volume which represents about 90-95% conversion of substrate to ethanol.

Glucose + Yeast = Ethanol + Carbon dioxide

Recovery of ethanol

The mass is separated by centrifugation in a centrifuge. Ethanol from fermentation broth can be recovered by distillations. For a concentration above 95%, distillation method is adopted. For 100% alcohol a specific type of distillation known as azeotropic distillation is used.⁸

For this an azeotrope mixture of Benzene, water, alcohol is first prepared after which the mixture is distilled by gradually increasing the temperature. By this technique, firstly benzene-ethanol-water then releases leaving behind only 100% alcohol.

CONCLUSION

100% alcohol is left after release of benzene-ethanol-water.

Glycolysis and alcoholic fermentation. (Source:
http://www.icr.org/article/172/)

Ethanol fermentation. (Source: http://slideplayer.com/slide/8809068/)

REFERENCES

1. G. Van den Thillart, Verhagen Maria, Waarde V.A.”Ethanol formation and pH regulation”. 1993: 157-170.
2. Raj SB, Ramaswamy S. “Yeast alcohol dehydrogenase structure and catalysis”. 53:5791-803.
3. Dengis, Pascale B, Nelissen L.R. Paul G. “Mechanisms of Yeast Flocculation: Comparison of top & bottom fermenting starins”.Applied and Environmental Microbiology: 1995: 718-728.
4. Omura F. Targeting of mitochondrial Saccharomyces cerevisiae to cytosol and its effect on vicinal diketone formation in brewing. Applied microbiology and biotechnology. 2008:503-513.
5. Fleet G. The microbiology of alcoholic beverages. Microbiology of fermented foods: 1997: 217-262.
6. Barnett J. “History of research on yeast; Louis Pasteur & his contemporaries: 2000. 1850-1880.
7. Nevoigt, Elke, Pilger, Schimdt.” Genetic engineering of brewing yeast to reduce the content of ethanol in beer”. 2002: 225-232.
8. Kister, Henry Z. “Distillation Design”. 1992: 1^st edition

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