Yeast makes bread and some cakes fluffy by eating sugar and releasing carbon dioxide gas—the same gas that’s in fizzy drinks! 🌬️
This process is a type of biological leavening called fermentation. Here’s a simple breakdown of how it works.
How Yeast Makes Bread Fluffy 🍞
- Yeast is Alive: Yeast is a tiny, living, single-celled organism (a type of fungus) that is dormant until it gets warm and wet.
- It Gets Hungry: When you mix yeast into dough with flour and water, it “wakes up” and starts to eat the simple sugars available in the flour.
- It “Burps” Gas: As the yeast feeds on the sugar, it releases two byproducts:
- Carbon Dioxide (
) Gas: This is the key to making bread rise.
- Alcohol (Ethanol): This mostly bakes off in the oven but adds to the bread’s final flavor and aroma.
- Carbon Dioxide (
- Gas Gets Trapped: The flour in the dough contains proteins that, when kneaded, link together to form an elastic, stretchy network called gluten. This gluten network acts like a balloon, trapping the tiny bubbles of carbon dioxide gas the yeast produces.
- Dough Rises: As the yeast produces more and more gas, these bubbles inflate the gluten network, causing the entire ball of dough to expand and “rise.”
- Baking Sets the Shape: When you put the dough in a hot oven, the heat causes the gas bubbles to expand rapidly (giving the bread one last “puff”), and then it sets the gluten structure in place. This leaves behind a light, airy, and fluffy texture full of tiny holes.
What About Cakes? 🎂
This is a great question, as it highlights an important difference in baking!
While some traditional cakes like Babka, Panettone, or Savarin do use yeast, the fluffy texture in most cakes you’re familiar with (like a birthday cake, cupcake, or sponge cake) is not created by yeast.
Instead, most cakes get their fluffiness from chemical leaveners:
- Baking Powder
- Baking Soda
These powders work much faster than yeast. As soon as they get wet (and in the case of “double-acting” baking powder, heated in the oven), they create a chemical reaction that releases carbon dioxide gas.
Just like with yeast, this gas creates bubbles in the batter that get trapped, causing the cake to rise and become light and fluffy. The main difference is that cake batters are not kneaded to develop gluten; in fact, the goal is to keep them tender, not chewy like bread.