Why Does Dough Puff Up When You Bake It? (2024)

When you think of bread, what comes to mind? Soft, fluffy slices that wrap perfectly around peanut butter and jelly? Warm dinner rolls covered in butter? A fungus fermenting and creating gas and other by-products?

The first two suggestions might have come to mind, but we doubt that many of you think of a fungus when you hear the word “bread." Without millions and millions of fungi, though, bakers would never be able to create the delicious breads we love to eat.

It's true! If you've ever baked bread at home, you know that one thing required is patience. After you mix all the ingredients together, you have to wait for a while for the dough to rise before you can bake it into yummy bread. Why do you have to wait? What's going on that causes the bread dough to puff up and rise?

The answers to these questions all revolve around one key ingredient: yeast. You've probably heard of yeast, but you might not know exactly what yeast is. If you've baked bread at home before, you probably know that yeast often comes in small packets you can buy at the grocery store.

Those little packets of yeast are filled with billions of single-celled fungi that scientists call Saccharomyces Cerevisiae (“sugar-eating fungus"). That's right! One of the key ingredients in most types of bread is a fungus!

Before you say “Ewww!" though, remember that fungi can be very helpful, as well as tasty. Those mushrooms on your pizza? Those are fungi! Also, some of your favorite cheeses are ripened with the help of certain molds.

Yeast cells that come in those little packets from the grocery store are living organisms. When packaged, they just happen to be in a dormant state, which means they're inactive. Just add them to some warm water, though, and they come alive!

In bread dough, the yeast cells mix with warm water and begin to feed on sugars, such as sucrose, fructose, glucose, or maltose, which come from the sugar and flour in the dough. As yeast cells feed on sugars, they produce carbon dioxide gas and ethyl alcohol in a chemical process known as fermentation.

The carbon dioxide gas released by the process of fermentation gets trapped in the sticky, elastic dough, causing it to “puff up" or rise. This can take a while, though, which is why you need patience when you're baking bread! Likewise, the ethyl alcohol produced gives the bread its unique smell and taste.

Heat can speed up the process of fermentation, which explains why bread continues to rise in the first few minutes of baking in the oven. Once the bread gets too hot, though, the yeast cells will die. The pockets of carbon dioxide gas left behind leaves tiny holes all throughout the bread, giving it its unique texture and softness.