There are indefinitely many combinations and proportions of types of flour and other ingredients, and also of radically different traditional recipes and modes of preparation of bread. As a result one finds wide varieties of types, shapes, sizes, and textures of breads in various regions. Bread may be leavened by many different processes ranging from reliance on naturally occurring microbes (for example in sourdough recipes) to high-pressure artificial aeration during preparation and/or baking. However, some products simply are left unleavened, either for preference, or for traditional or religious reasons. Many non-cereal ingredients may be included, ranging from fruits and nuts to various fats. Commercial bread in particular commonly contains additives, some of them non-nutritional, to improve flavour, texture, colour, or shelf life.
Depending on local custom and convenience, bread may be served in various forms at any meal of the day. It also is eaten as a snack, or used as an ingredient in other culinary preparations, such as fried items coated in crumbs to prevent sticking, or the bland main component of a bread pudding, or stuffings designed to fill cavities or retain juices that otherwise might drip away.
Partly because of the immemorial worldwide importance of bread as a basic foodstuff, traditionally a food often hard come by, bread has taken on a social and emotional significance beyond its importance in nutrition; it plays essential roles in religious rituals and secular culture. Its prominence in daily life is reflected in language, where it appears in proverbs ("Bread falls on the buttered side.") colloquial expressions ("He stole the bread from my mouth.") in prayer ("Give us this day our daily