How to Use Yeast Bubbling in Experiments

Perform a simple experiment by mixing two tablespoons of sugar, a sachet of baker's yeast and a cup of hot-but-not-boiling-water in a plastic bottle. Stretch a balloon over the neck of the bottle and give the bottle a gentle shake. The balloon will inflate over 10 or 15 minutes.

Test that the gas being produced is carbon dioxide by repeating the experiment above but instead of capping the bottle with a balloon, put a hose over the end and seal with tape. Put a test tube in a fish tank full of water. Fill it with water, invert and draw to the surface to suspend a water column.

Position the end of the rubber hose not joined to the bottle in the water underneath the test tube. The bubble from the yeast will fill the test tube. When it is half-full, remove the test tube, but keep it inverted. Insert a burning length of paper. The carbon dioxide will cause it to extinguish.

Investigate how the temperature affects the rate of gas production. Repeat the procedure in the previous step, but use a measuring cylinder instead of a test tube. Measure how much gas the yeast produces in three minutes by looking at how much water it displaces from the tube. Repeat the experiment, using water at different temperatures to mix with the yeast. See how this influences the rate of gas production.

Repeat the procedure given above, but don't change the temperature of the water. Instead, change the amount of sugar you use each time, varying by half a teaspoon for each experiment.