The common kitchen ingredient used to raise bread is yeast. Yeast is a type of fungus that ferments sugars to produce carbon dioxide and alcohol during the process of fermentation. When making bread, the carbon dioxide gas released by the yeast gets trapped in the dough's gluten structure, causing it to rise and develop a light and airy texture. There are different types of yeast used in baking, including active dry yeast, instant yeast, and fresh yeast. The fermentation process not only helps the bread rise but also contributes to its flavor.