This is a very simple and fast demonstration, however I think is a nice one and you can show it to your kids, I'm sure they are going to be impressed and they will learn something about bread making.
Step 1: Saccharomyces cerevisae and CO2
Saccharomyces comes from Greek meaning sugar mould and Cerevisiae comes from the Latin meaning of beer.
Bread making is known since ancient times (archeologists have found evidences of bread making in ancient Egypt.) and Saccharomyces cerevisae is responsible for many of the desirable characteristics in bread.
When Saccharomyces is added to the dough, it changes sugars present in the flour or added to the dough, giving off carbon dioxide (CO2) and alcohol (ethanol). The CO2 is trapped as tiny bubbles in the dough and expands the flour's gluten proteins, and as a result, causes the dough to rise, while alcohol is rapidly evaporated during baking. This process is called fermentation and is the way for gaining energy for many microorganisms
So, in bread making, the carbon dioxide is the more important of the two products, with the evolving gas causing the bread dough to rise. On the other hand, in beer and wine-making, the alcohol is the important product, although the carbon dioxide may be used in beer and champagne.
Shacharomyces is not only important for food and beverage production but for genetic investigation.
Because of the importance of this yeast in Industry and the role of CO2 in breadmaking, I think it could be interesting to use it for the Science Fair contest so I designed this simple experiment to demonstrate the production of CO2 during Saccharomyces cerevisae sugar fermentation.
To do this, we are going to make a very simply home apparatus to collect the CO2 produced during fermentation and then, will conduct it into a red cabbage solution which will act as a pH indicator.
We will need a pH indicator to demonstrate the presence of CO2 because when we make CO2 solution in water it forms carbonic acid (H2CO3), so we can detect the formation of this acid using a pH indicator.