Why does bread rise?
Bread rises because yeast eats sugars in the dough and releases carbon dioxide gas. Stretchy gluten in the dough traps the gas bubbles, making the dough expand.
Yeast is a living single-celled fungus. When it is mixed into dough, it feeds on sugars from the flour and produces carbon dioxide and alcohol through fermentation. Kneading the dough develops gluten, a network of proteins from wheat flour, which forms elastic walls around the gas bubbles, like tiny balloons.
Warmth speeds up yeast activity, which is why dough is often left to rise in a warm place. Too much heat, though, can kill the yeast. When the bread bakes, the gas expands quickly, giving a final rise called oven spring. The heat then sets the structure, and the alcohol evaporates.
Other ways to make bread rise
Quick breads, such as soda bread and many muffins, use baking soda or baking powder instead of yeast. These chemical leaveners release carbon dioxide when mixed with liquid or acid and heated. Sourdough rises with wild yeast and bacteria.
Did You Know?
Gluten-free bread is harder to make because it lacks gluten to trap gas, so bakers use ingredients like xanthan gum or psyllium husk to help.