Yeast is such a common thing that we don't give much thought to how amazing it is, and what a boon it is to bakers, brewers, and winemakers. And yeast is such a fun guy. Or, more accurately, a fungi. It converts the fermentable sugars in the dough into carbon dioxide and ethanol, and those bubbles, trapped in the matrix of gluten, are what causes bread to rise. When the dough is baked, the yeast dies but the pockets of air remain, giving the bread its unique texture.