An ingredient used in many foods, flour is a fine powder made from grain or other starchy food sources. It is most commonly made from wheat, but also maize (aka corn), rye, barley and rice, amongst many other grasses and non-grain plants (including many Australian species of acacia).
Flour is always based on the presence of starches, which are complex carbohydrates.
Usually, the word "flour" used alone refers to wheat flour, which is one of the most important foods in European and American culture. Wheat flour is the main ingredient in most types of breads and pastries. Wheat is so widely used because of an important property: when wheat flour is mixed with water, a complex protein called gluten develops. The gluten development is what gives wheat dough an elastic structure that allows it to be worked in a variety of ways, and which allows the retention of gas bubbles in an intact structure, resulting in a sponge-like texture to the final product. This is highly desired for breads, cakes and other baked products.
A coarser preparation, somewhat granular rather than a fine dust, is often called meal.
Types of Flour
- The vast majority of today's flour consumption is wheat flour.
- Wheat varieties are typically known as "hard" or "strong" if they have high gluten content, and "soft" or "weak" if gluten content is low. Hard flour, or "bread" flour, is high in gluten and so forms a certain toughness which holds its shape well once baked. Soft flour is comparatively low in gluten and so results in a finer texture. Soft flour is usually divided into "cake" flour, which is the lowest in gluten, and "pastry" flour, which has slightly more gluten than cake flour.
- All-purpose flour is a blended wheat flour with an intermediate gluten level which is marketed as an acceptable compromise for most household baking needs.
- In terms of the parts of the grain (the grass seed) used in flour -- the endosperm or starchy part, the germ or protein part, and the bran or fiber part -- there are three general types of flour. "White" flour is made from the endosperm only. "Whole grain" flour is made from the entire grain. A "germ" flour may also be made from the endosperm and germ, excluding the bran.
- "Whole-wheat" flour is also referred to as "graham" flour in the USA, and is the basis of true graham crackers. Many graham crackers on the market are actually imitation grahams because they contain no whole-wheat flour. Strictly speaking, a true graham flour is a coarse grind of wheat.
- Self-rising or self-raising flour is "white" wheat flour that is sold premixed with chemical leavening agents. Typical ratios are
U.S. customary: one cup flour : 1 to 1 1/2 teaspoon baking powder : a pinch to 1/2 teaspoon salt
Metric: 1 kg flour : 30 g baking powder : 10 g or less salt
- Maize flour is very popular in the southern United States and in Mexico. In the US, "white" corn (maize) flour is usually referred to as cornstarch; in the UK it is known as cornflour. "Whole-grain" corn flour is usually referred to as corn meal. Corn meal which has been leached with lye is called masa harina and is used to make tortillas and tamales in Mexican cooking.
- 100% Rye flour is used to bake the traditional sourdough breads of Germany and Scandinavia. Most rye breads use a mix of rye and wheat flours because rye has a low gluten content. Pumpernickel bread is usually made exclusively of rye, and contains a mixture of rye flour and rye meal.
- Rice flour is of great importance in Southeast Asian cuisine. Also edible rice paper can be made from it. Most rice flour is made from white rice, thus is essentially a pure starch, but whole-grain brown rice flour is commercially available.
In some markets, the different available flour varieties are labeled according to the ash mass that remains after a sample was incinerated in a laboratory oven at 900 °C (ISO 2171, method A). This is an easy to verify indicator for the fraction of the whole grain that ended up in the flour. The "flour type" number given in many German bread recipes is the amount of ash (measured in milligrams) obtained from 100 g of this flour. Standard wheat flour types (DIN 10355) range from 405 for normal white flour to 1600 for flours used in dark breads. Wholemeal flour leaves 2000 mg ash or more per 100 g.
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 water-operated mill, in which a revolving stone wheel turns over a stationary stone wheel, with the grain in between. Many small appliance mills are now available, both hand-cranked and electric.
Flour dust suspended in air is explosive, as is any mixture of a finely powdered flammable substance with air see Lycopodium. Some of the worst civilian fatalities from explosions have been at flour mills.
In history, both large and hand mills were operated. Until modern times, much flour contained minute amounts of grit, either the result of poor sifting of the grain or of grinding stones together. This grit strongly abraded teeth.
One of the most ancient methods of grinding to produce flour was by using a pair of quern-stones. These were made out of rock, and were ground together by hand. They were generally replaced by millstones once mechanised forms of milling appeared, particularly the water mill and the windmill, although animals were also used to operate the millstones.
Bread, pasta, crackers, many cakes, amongst many other foods, are made using flour. Wheat flour is also used to make a roux as a base for gravy and sauces. White wheat flour is the traditional base for wallpaper paste. It is also the base for papier-mâché. Cornstarch is a principal ingredient of many puddings.