We have been making bread together (great boredom buster and it’s helping my 2nd grader understand fractions). Because of our bread baking we’ve observed that some breads come out more fluffy than others. This has led to a lot of questions, so I thought it would be fun to do a kitchen experiment to explain what is happening.

I’ve included a worksheet that has most of this information already on it. It has a download link below.

What You Need:

• clean soda or water bottle (a smaller one with a neck works best. We happened to have a conical flask purchased for a Harry Potter Party prop).
• 2 tsp. yeast
• 2 tsp. sugar
• 1 cup warm water
• 1 balloon
• 1 rubberband

What We Did

We started by observing yeast. I had my kids draw what it looks like. Then we watched this YouTube video that showed yeast under various microscope magnifications.

We drew a picture of what yeast looked like under a microscope. We talked about how yeast is a microorganism. Which means it is a very tiny living thing.

I told them how yeast is usually kept cool and dry until we are ready to use it. While it is cool and dry it is dormant. We are going to find out what is needed to make it active.

Next we experimented!

Add the water to your bottle.
Add the yeast, followed by the sugar and stir to dissolve.
Quickly cover the opening of the bottle with the balloon and use the rubberband to keep it on tight.

Watch

We observed what happened to the balloon. What we saw happening in the bottle, and how long it took. I asked them if they knew how the balloon got bigger. They guessed correctly that the yeast must be creating a gas. I explained that the yeast created a gas called Carbon Dioxide. I asked if they had ever heard that word before and they knew that it was the gas we breathe out when we exhale. They drew a picture of what they observed.

So How Does Yeast Make Bread Fluffy?

We took out a slice of bread and observed it. I pointed out the small bubbles in the bread, and we talked about how yeast is added to bread dough along with warm water and often some kind of food like sugar. This makes the yeast created carbon dioxide with causes the bubbles. Both of my kids were kind of grossed out at the thought of eating yeast and I explained that when the bread is cooked the yeast dies. The bubble they created expand as moisture in the bread turns to steam. We followed up this experiment by making a loaf of bread and paying attention to how much it rises. But I’ve also included a YouTube video time lapse here.