CARBON DIOXIDE AND YEAST EXPERIMENTS

Most children have no idea what yeast is, or how it is used. When I explain to them that bread, rolls, and cake are made from yeast the kids got interested.

 I start by telling them that yeast is a living organism, a fungus.  As a living  organism it needs the same things to live as humans and it gets old just like we do. Its life span is only 6 months after its container has been opened and it must be kept in the refrigerator..  Then I ask what people needed to keep alive. Almost always the kids will guess oxygen, food, and water.  When I tell them that the the yeast needs the same oxygen, food and water to live and just like them the yeast breathes out the gas carbon dioxide. Yeast also needs warmth to grow. If one element is missing the yeast will not grow.  Lets' do an experiment to prove that 1. yeast needs oxygen and gives off carbon dioxide, 2. yeast needs sugar for food , 3. water to grow, and 4. warmth.

We set up 3 small soda bottles. In one bottle with the blue balloon we put yeast and water, no food.  In another bottle with the yellow balloon we put fresh yeast, sugar, and water.  In the third bottle with the green balloon we put old yeast, sugar, and water. We put different colored balloons to be able to keep track of which experiment it was.  We used 1 tablespoon yeast, and sugar and 1/4  water in each.

We set the bottles on the top of the stove and put the oven temperature to 200 degrees because it was winter and my house temperature is only  64 degrees. Yeast needs 75 degrees. A lamp would give warmth also.

The yellow balloon bottle with the new yeast, sugar and warm water is growing big because it has food is creating the gas carbon dioxide. Just like people yeast needs food to grow bigger.

The new yeast with food continued to produce carbon dioxide and grow bigger.

·        The balloon of the bottle of old yeast (green) just stood up but did not grow. This proves that new yeast is needed to make bread rise.  The balloon of the bottle of yeast without food (blue) only stood up but did not grow proving that yeast needs food to grow and produce carbon dioxide--just like people.

·        The total time we needed for this experiment was 2 hours.