What is usually put in bread to make it swell?

Here's how it works:

* Yeast is a living organism that feeds on sugar.

* When yeast is added to dough, it ferments the sugar, producing carbon dioxide gas.

* This gas gets trapped within the dough, causing it to expand and rise.

* The gluten in the dough, a protein formed from the mixing of flour and water, provides a structure that holds the gas and keeps the bread from collapsing.

So, the combination of yeast and gluten creates the fluffy texture that we love in bread.