The substance usually added to bread dough to help it rise is yeast. Yeast is a microorganism that ferments sugars and produces carbon dioxide gas and alcohol, which contributes to the leavening process. As yeast consumes the sugars present in the dough, it releases carbon dioxide, creating bubbles that cause the dough to rise and develop a light, airy texture. This fermentation process also adds to the flavor of the bread. Various types of yeast, such as active dry yeast and instant yeast, are commonly used in baking. The presence of yeast is essential in many types of bread, rolls, and other baked goods.