Bread is a staple food around the world that is prepared by baking dough of flour and water. It may be leavened or unleavened. Salt, fat and a leavening agent such as yeast are common ingredients, though breads may contain a range of other ingredients: milk, egg, sugar, spice, fruit (such as raisins), vegetables (such as onion), nuts (such as walnuts) or seeds (such as poppy seeds)