Producing Ethanol by Fermentation

Ethanol (C2H5OH) is a type of alcohol found in alcoholic drinks like beer and wine, but it also has other uses such 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 then undergoes anaerobic respiration, using glucose to produce ethanol and carbon dioxide. This reaction takes place slowly, usually over the course of several days or even weeks.

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 reaches around 15%, the yeast dies and the mixture becomes 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

To ensure successful fermentation, the following conditions are required:

  • Sugars need to be dissolved in water and yeast must be added
  • The temperature of the mixture should be 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.