Inflate a Balloon with Yeast Experiment

Did you know that you can inflate a balloon WITHOUT blowing air into it? It’s true.

In this simple experiment, young scientists use yeast to magically inflate a balloon. How cool is that?!

Check out the simple step-by-step below and then snag our 30 Science Experiments that are kid-approved!

Getting Ready

We headed into the kitchen to grab all of our supplies for this science experiment:

• Clear plastic or glass bottle with a narrow neck (a water bottle or soda bottle work great)
• 2 Tablespoons dry yeast
• 1 Tablespoon sugar
• 2-3 Tablespoons lukewarm water
• Party balloon
• Bowl or mug full of lukewarm water

Inflating a balloon with yeast is a wonderful experiment to do with preschool and kindergarten aged children because all of the materials are nontoxic. It’s nice when the kids can help measure out ingredients without worrying about what they are touching.

My kids helped me measure the yeast, sugar, and warm water into a cup.

They stirred the ingredients and then used a funnel to pour the brown mixture into the bottle. We added a little bit more water to help the yeast mixture get through the neck of the funnel.

We quickly stretched a balloon over the mouth of the bottle.

After placing the bottle into a mug full of warm water, we sat back to observe.

Inflate a Balloon with Yeast

Almost immediately, we observed bubbles in the yeast mixture.

I explained to the kids that yeast is a microscopic fungus that converts sugar into carbon dioxide.

The bubbles they saw were tiny bubbles of carbon dioxide gas that the yeast was producing as it “ate” the sugar.

For yeast to be active, it needs to be warm and moist. That’s why we added lukewarm water and placed the bottle in more warm water.

We set our bottle of yeast on the table and watched it while we ate lunch and read books.

We checked in with our science experiment every 10 minutes or so to observe any changes. Every time we looked, we noticed that the balloon was getting bigger and bigger on top of the bottle! Why?

As the yeast continued to react, it converted more and more sugar into carbon dioxide gas.

This gas was trapped in the balloon, making it inflate as if by magic!

It took about an hour for our balloon to reach its maximum size.

The yeast bubbled up into the bottle quite a bit before it stopped reacting and shrank down again. Simple science at its best.

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