Sunday, 15 May 2011


This practical can be done as a demo or class experiment provided you have enough materials for the whole class.

Fermentation is the process of breaking down of food by micro-organisms using anaerobic respiration. Yeast is a single-celled fungus, and reproduces by growing buds out of the cell and feeds itself on sugars like glucose. In the process of fermentation, the yeast makes alcohol (Ethanol) and carbon dioxide. To illustrate it better, consider the equation below

The Equation:


• boiling tubes / (you may use conical flask)
• boiling tube bung and delivery tube
• yeast
• sugar
• 1000ml beaker
• 100ml beaker
• limewater
• test tube

a. Using the 100ml beaker, put a spoonful of yeast and sugar, and add 50ml of warm water ( not boiling water, otherwise it would kill the organism)
b. Mix them properly until the yeast and sugar are dissolved.
c. Pour enough amount of the mixture into the boiling tube.
d. Put the bung and delivery tube and run this into the test tube with limewater.
e. Observe the colour of the limewater. It should turn cloudy due to carbon dioxide that is given off by the mixture.

NOTE: It is more exciting to collect the carbon dioxide using balloons. It is preferable to use conical flask instead of the boiling tube. Increase the amount of the mixture and put it in the conical flask. Collect the carbon dioxide by putting on the balloon at the opening and wait for 20-30 minutes to see the balloon slowly starting to inflate. You can leave it for few hours but not overnight. It may burst out and will surely create a mess. The mixture has an odd smell.

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