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Fermentation of Ethanol

  • Yeast can break down glucose by anaerobic respiration to produce ethanol.
  • Sugar cane juices or glucose from maize starch can be used by the enzyme carbohydrase
  • Before use, the ethanol has to be distilled
  • The ethanol can be mixed with petrol to produce 'gasohol' which is better for the environment than conventional fuels.
  • Burning ethanol is a carbon neutral process as the plants release the carbon dioxide they took in whilst they were still growing.
  • However the fermentation of ethanol uses edible parts of the plant which could otherwise be used to feed starving people. It also uses deforested land to have enough space to grow the crops so this can't be done in other areas.


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Fermentation to produce Biogas

  • Biogas is about 70% methane and 30% Carbon Dioxide
  • Biogas is produced in a generator - or fermenter
  • Biogas uses different microorganisms which ferment plant and animal waste in anaerobic conditions.
  • Biogas generators need a variety of modifications in order to maintain tha rate of the respiring bacteria to break down the waste to produce biogas.
  • There are two types if generators: Batch Generators and Continuous Generators.
  • Human waste, food waste and animal waste can be digested by bacteria to produce biogas for a family or village.
  • The by-products of fermentation of these products can also be used to fertilise crops so it is not wasted. 
  • Biogas also reduces the amount of methane in the atmosphere as it is all contained in the generator for use as a fuel.
  • It is cheap and available
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Fermentation to produce Mycoprotein

  • Mycoprotein is produced by fusarium in a fermenter.
  • Glucose syrup acts as the culture medium is obtained by digesting maize starch with enzymes and is used as a food source for the microorganisms to grow and reproduce in.
  • The fungus respires aerobically so oxygen needs to be supplied.
  • There is also a stirrer to evenly distribute the temperature, Oxygen and food source.
  • The fermenter is initially sterilised to prevent other microorganisms growing in it.
  • The biomass is then harvested and purified, it has a very high amount of protein and is relatively low in fat. 
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A Basic Fermenter

  • There are temperature and pH monitors which enable us to ensure that the bacteria have the right conditions for respiration.
  • There is also a stirrer to evenly distribute the temperature, Oxygen and food source and keep the respiring bacteria in suspension.
  • The water cooled jacket removes any excess heat from the respiring bacteria to maintain the constant conditions needed.
  • Nutrients and air entering the fermenter are sterylised to prevent other bacteria growing in the fermenter.

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A Biogas Generator

  • All Biogas generators have: an inlet for the waste material to be fed in.
  • An outlet fo the digested material to be used as a fertiliser.
  • A biogas outlet leading straight to the home.
  • Some may be buried underground to maintain the constant warm temperatures-(around 30 degrees Celcius) more easily.


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