Growing bread yeast in plastic baggies is a fun way for your child to practice some easy math and learn about the living organisms that make bread puffy.
What You'll Need
- Plastic zipper baggies
- Active dry yeast (four 2 ½ tsp. packages)
- Salt
- Sugar
- Water
- Magnifying glass (optional)
How to Make Yeast Balloons
Step 1: Help your child label four zipper baggies as follows:
- "Sugar + warm water"
- "Sugar + cold water"
- "Sugar + salt + warm water"
- "No sugar + warm water"
Step 2: Let your young scientist add a package of yeast (or 2 tsp.) to each plastic bag. Ask her to smell the yeast. Does it feel dry? Look at the yeast under a magnifying glass, if you have one. Remind your child that yeast is a living thing and that we use it to make baked goods like bread and pizza dough puff up.
Step 3: Have your child add 2 tsp. of sugar to each of the three bags that say "sugar" and 1 tsp. of salt to the bag that says salt.
Step 4: Ask her to find the 1 cup mark on a liquid measuring cup. Then have her find the ½ cup mark and fill the measuring cup with ½ cup of water.
Step 5: Help your child read the labels to decide whether to add warm (not hot) or cold tap water to each bag. Assist by holding the bags open as she adds ½ cup water to each baggie. Seal the bags, squeezing out as much of the extra air as possible and let them sit on a tabletop or counter at room temperature. (The yeast will grow faster in a warm room than a cold one.)
Step 6: Ask your child to guess what will happen when the yeast starts to grow. Have her check the bags every 15 minutes. When the baggies start to puff up, it means that the yeast are growing. Let her take pictures of the baggies or draw what is happening.
Note: Keep an eye on the experiment. If a bag gets so puffy that it looks like it might explode, be sure to open it to let some pressure out and avoid a mess!
Step 7: After an hour or so, talk about the results of the experiment. Ask your child questions such as, “Which ingredients help yeast grow best? Was there an ingredient that kept them from growing well? Do yeast cells grow faster in warm or cold water? What do you think makes the bags puff up and how does this tell you that the yeast is growing? Can your child find the tiny holes left by yeast in a piece of bread?”
The Science Behind the Fun
In 1857, a famous scientist named Louis Pasteur proved that tiny living organisms called yeast are responsible for making bread rise.
The yeast cells used to make bread are shaped like balloons and footballs. They love to eat sugar and starches and as they grow, they make carbon dioxide gas. In bread dough, the gas forms lots of tiny bubbles that pop during baking, leaving tiny holes.
In this experiment, the yeast eats sugar and the carbon dioxide gas they create is trapped in sealed plastic bags, making them blow up like balloons.
You can find more experiments like this one at kitchenpantryscientist.com, and in my books Kitchen Science Lab for Kids (Quarry Books) and Outdoor Science Lab for Kids (Quarry Books).
© Quarry Books, 2016/Kitchen Science Lab for Kids
Featured Photos Credit: © Quarry Books
