The yeast consumes the natural sugars in the dough and causes bubbles to form. This causes the dough to rise. It's being blown up by the yeast.
Carbon dioxide
Yes, dough can rise in the fridge, but it will rise more slowly than at room temperature. This process is called cold fermentation and can enhance the flavor of the dough.
The fermentation (growth of microorganisms as they digest sugar) in any yeast dough is obvious when the dough rises. If the dough does not rise, you know that fermentation has not taken place.
Alcoholic fermentation
carbon dioxide
usually yeast is the substance
Fermentation causes bread dough to rise. Certain yeasts and bacteria are capable of producing energy from sugars through fermentation. Yeast such as S. cerevisiae causes bread dough to rise. - Intro to Biotechnology (Third Edition): Thieman & Palladino
The product of alcoholic fermentation that causes dough to rise and creates the little holes in bread is carbon dioxide. During fermentation, yeast converts sugars into alcohol and carbon dioxide gas, which gets trapped in the dough. This gas expands when heated during baking, leading to the dough rising and forming the characteristic holes in the bread.
The gas that bubbles in the dough to make it rise is carbon dioxide. This gas is produced during fermentation by yeast or chemical leavening agents. The carbon dioxide forms bubbles in the dough, causing it to expand and rise.
Fermentation - creates bubbles of carbon dioxide... which causes the dough to rise, and gives bread light, open texture.
Both types of fermentation are used in various commercial processes. Lactic acid fermentation is used to make yogurt. Alcoholic fermentation is used to make dough rise.
fermentation starts as soon as the water sugar and yeast is mixed into the flour to make a dough.this is the period when the dough is left to rest and rise till double in size before it is knocked back and portioned for further shaping / moulding. proofing is the period when the shaped / moulded dough is rested till double in size before baking.