Producing Ethanol by Fermentation

Ethanol (C2H5OH) is a type of alcohol found in alcoholic drinks, such as beer and wine. It also has other uses, such as serving as a fuel for vehicles and as a solvent. Ethanol can be produced naturally through the process of fermentation, which involves the conversion of sugars into ethanol and carbon dioxide.


During fermentation, plant material containing sugar (glucose) is mixed with yeast, which is a single-celled fungus that contains the necessary enzymes for the reaction. The yeast undergoes anaerobic respiration, converting glucose into ethanol and carbon dioxide. This reaction usually takes several days or even weeks to complete.

The chemical equation for the fermentation of glucose is:

Glucose + Enzymes Ethanol + Carbon Dioxide

C6H12O6 + Enzymes 2C2H5OH + 2CO2

The rate of fermentation is affected by temperature. Fermentation occurs faster at higher temperatures. However:

  • If the temperature is too low, fermentation will take place very slowly or may not occur at all.
  • If the temperature is too high, the enzymes become denatured, so fermentation stops.

Yeast can only survive in a certain concentration of ethanol. Once the concentration of ethanol reaches around 15%, the yeast dies, making the mixture vulnerable to oxidation by air. This can cause the ethanol to turn into ethanoic acid, giving the mixture a sour taste similar to vinegar. To avoid this, the reaction vessel is emptied and the process is restarted.

The production of ethanol by fermentation is a batch process, which means it is produced in a series of batches rather than continuously.

Conditions Required for Fermentation

For successful fermentation, the following conditions must be met:

  • Sugars should be dissolved in water, and yeast must be added
  • The mixture’s temperature should be maintained between 25 and 35°C
  • An airlock is used to allow carbon dioxide to escape and prevent air from getting in, so that the yeast can continue to respire anaerobically.

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