How does yeast produce gas?

Yeast is a microscopic being that needs sugar to live. It consumes sugar and instead produces a gas called carbon dioxide that is used, for example, in making bread: the gas makes the dough rise, making it lighter and fluffier when baked. For cooking you can use fresh or dry yeast.

Material:

•  A bag of dry yeast
• A little fresh yeast
• White granulated sugar
• A coffee jar
• A dropper
• A piece of plasticine

Process:

Dissolve a little sugar in the water, add yeast to it and stir well. Scoop up some of the mixture with the eyedropper and, with the piece of clay, hold the eyedropper to the inside of the jar. Add some lukewarm water so that the tip of the dropper is well below the surface. Gas bubbles will immediately begin to form in the mixture from the dropper, which will come out of the tip, and which you can count.

Now try to:

• Vary the temperature of the water in the jar
• Add more sugar to the solution
• Mix yeast with glucose instead of sucrose
• Use a different yeast, for example the one used in breweries