Protein and water molecules naturally combine over time, further expanding the two gluten tissues. On the one hand, it is supported like an elastic skeleton that runs through the whole dough, on the other hand, it is stretched like a rubber band and then covered with gas.

Yeast absorbs and decomposes sugar, producing carbon dioxide gas and alcohol under anaerobic respiration and carbon dioxide gas and water under aerobic respiration. So after fermentation, the dough becomes bigger and the surface is more sticky. If it takes too long, it will smell of alcohol and yeast fermentation.