In baking, rising is a physical process that happens because of fermentation. This process can be from a chemical reaction (with chemical leaveners, like baking soda), or from a biological process (with yeast of soughdough starter). Either way, what happens in these reactions that make the dough rise is the release of carbon dioxide (CO2), which can occur in the chemical reaction of baking soda with an acid (baking powder, for example, is composed of baking soda and cream of tartar), or it occurs in a biological process, when the yeast feeds itself from the sugars in the dough, releasing CO2 and alcohol.