Bread is a staple food prepared from a dough of flour and water, usually by baking. Throughout recorded history it has been popular around the world and is one of the oldest artificial foods, having been of importance since the dawn of agriculture. Proportions of types of flour and other ingredients vary widely, as do modes of preparation. As a result, types, shapes, sizes, and textures of breads differ around the world. Bread may be leavened by processes such as reliance on naturally occurring sourdough microbes, chemicals, industrially produced yeast, or high-pressure aeration. Some bread is cooked before it can leaven, including for traditional or religious reasons. Non-cereal ingredients such as fruits, nuts and fats may be included. Commercial bread commonly contains additives to improve flavor, texture, color, shelf life, and ease of manufacturing. Bread is served in various forms at any meal of the day. It is eaten as a snack, and used as an ingredient in other culinary preparations, such as sandwiches, and fried items coated in crumbs to prevent sticking. It forms the bland main component of bread pudding, as well as of stuffings designed to fill cavities or retain juices that otherwise might drip away. Bread has a social and emotional significance beyond its importance as food. It plays essential roles in religious rituals and secular culture. Its prominence in daily life is reflected in language, where it appears in proverbs, colloquial expressions ("He stole the bread from my mouth"), in prayer ("Give us this day our daily bread") and in the etymology of words, such as "companion" (from Latin com "with" + panis "bread").