Why does bread rise?
Yeast eats sugar, burps invisible gas, and a stretchy gluten net traps it.
The microbes do the heavy lifting
A pinch of yeast contains billions of single-celled fungi. Once they meet warm water and starch, they wake up and start metabolising, that is, eating.
Their meal is sugar (often broken loose from flour by enzymes). Their waste, usefully for us, is carbon dioxide gas plus a trace of ethanol.
Gluten is the net that catches the gas
loose flour + water
elastic dough
Kneading lines up two wheat proteins, gliadin and glutenin, into long strands that hook together into a stretchy mesh.
Heat sets the structure
yeast eats sugar
CO₂ inflates pockets
gluten stretches
oven heat sets it
In the oven, the gas expands further, the yeast finally dies, and the proteins and starches stiffen, locking the airy structure in place.