The main ingredient used in baking bread is flour, typically wheat flour. Flour provides the essential structure and carbohydrates necessary for bread to rise and become light and airy during the baking process. When mixed with water and yeast, the proteins in flour (mainly gluten) form a pliable dough. This dough captures the gases produced by yeast fermentation, allowing the bread to rise. Additional ingredients like salt, sugar, and fats can also enhance flavor, texture, and shelf life, but flour remains the primary component.