bread, food made from grains that have been ground into flour or meal, moistened and kneaded into a dough, and then baked. Many types of bread are leavened, usually with yeast, which induces fermentation and causes the breads to rise. The discovery of fermentation is attributed to the Egyptians, who also invented baking ovens. Unleavened flat breads have been eaten since Neolithic times (10,000 b.c.), and bread has long been a staple in the diets of people in all parts of the world, excepting Asia, where the preferred rice is eaten in grain form. Flat breads are made from various types of grains—corn (e.g., the tortilla), barley, millet, wheat, and rye—but only doughs made from wheat and rye contain enough gluten to trap the gases caused by fermentation and expand into an airy loaf of bread. Dark rye breads are common in Europe; the light rye breads popular in the United States are made with a mixed wheat and rye dough. White breads are made from a finely sifted wheat flour, as opposed to whole wheat bread, which retains the fiber-rich outer kernel of the grain. Nutritionally, bread is high in complex carbohydrates and a good source of B vitamins. Whole grain bread is higher in protein, has twice the fiber, and generally has more vitamins and minerals than white bread. Other ingredients that may be added to breads include milk, fats, eggs, salt, and sugar.