Flour is a powder which is made by grinding cereal grains, other seeds or roots (like Cassava). It is the main ingredient of bread, which is a staple food for many cultures, making the availability of adequate supplies of flour a major economic and political issue at various times throughout history. Wheat flour is one of the most important foods in European, North American, Middle Eastern, Indian and North African cultures, and is the defining ingredient in most of their styles of breads and pastries. Maize flour has been important in Mesoamerican cuisine since ancient times, and remains a staple in much of Mexico and parts of Central America. Rye flour is an important constituent of bread in much of central Europe. Milling of flour is accomplished by grinding grain between stones or steel wheels. Today, "stone-ground" usually means that the grain has been ground in a mill in which a revolving stone wheel turns over a stationary stone wheel, vertically or horizontally with the grain in between. Many small appliance mills are available, both hand-cranked and electric. The mill stones frequently rub against each other resulting in small stone particles chipping off and getting into flour, but they are removed before the flour is sold. [edit]Modern mills Main article: Gristmill Rollermills soon replaced stone grist mills as the production of flour has historically driven technological development, as attempts to make gristmills more productive and less labor-intensive led to the watermill[6] and windmill. These terms are now applied more broadly to uses of water and wind power for purposes other than milling.[7] More recently, the Unifine mill, an impact-type mill, was developed in the mid-20th century. [edit]Composition Flour being stored in large cloth sacks Flour contains a high proportion of starches, which are a subset of complex carbohydrates also known as polysaccharides. The kinds of flour used in cooking include all-purpose flour, self-raising flour, and cake flour including bleached flour. The higher the protein content the harder and stronger the flour, and the more it will produce crusty or chewy breads. The lower the protein the softer the flour, which is better for cakes, cookies, and pie crusts.[8] [edit]Unbleached flour Unbleached flour is simply flour that has not undergone bleaching and therefore does not have the color of "white" flour. An example of this would be the Graham flour. Sylvester Graham was against using bleaching agents, which he considered unhealthy. [edit]Bleached flour Main article: Flour bleaching agent "Refined flour" has had the germ and bran removed an is typically referred to as "white flour". "Bleached flour" is any refined flour with a whitening agent added. Bleached flour is artificially aged using a bleaching agent, a maturing agent, or both. A bleaching agent would affect only the carotenoids in the flour; a maturing agent affects gluten development. A maturing agent may either strengthen or weaken gluten development. The four most common additives used as bleaching/maturing agents in the USA at this time are: Potassium bromate (will be listed as an ingredient/additive) - a maturing agent that strengthens gluten development. Does not bleach. Benzoyl peroxide - bleaches. Does not act as a maturing agent - no effect on gluten Ascorbic acid (Will be listed as an ingredient/additive, but seeing it in the ingredient list may not be an indication that the flour was matured using ascorbic acid but instead has had a small amount added as a dough enhancer) - Maturing agent that strengthens gluten development. Does not bleach. Chlorine gas - both a bleaching agent and a maturing agent, but one that weakens gluten development. Chlorination also oxidizes starches in the flour, making it easier for the flour to absorb water and swell - this makes thicker batters and stiffer doughs. For bread, this is bad (because gluten is weakened and bread is heavily dependent on gluten formation), but for cakes, cookies, and biscuits, it's a good thing, because gluten development in these types of baked goods makes them tough. The modification of starches in the flour allows the use of wetter doughs (making for a moister end product) without destroying the structure necessary for light fluffy cakes and biscuits.[9] Chlorinated flour allows cakes and other baked goods to set faster, rise better, the fat to be distributed more evenly, with less vulnerability to collapse. Cake flours in particular are nearly always chlorinated. There is at least one flour labeled "unbleached cake flour blend" (marketed by King Arthur) that is not bleached, but the protein content is much higher than typical cake flour at about 9.4% protein (cake flour is usually around 6% to 8%). According to King Arthur, this flour is a blend of a more finely milled unbleached wheat flour and cornstarch, which makes a better end result than unbleached wheat flour alone (cornstarch is a common additive for part of the flour used in cake where actual cake flour is called for but you only have all purpose on hand). However you will still get a denser end result than real cake flour that has been more finely milled, chlorinated, and has a lower protein content in the "cake flour" range of around 6% or so.