An ingredient used in many foods, flour is a fine powder made from cereals or other starchy food sources. It is most commonly made from wheat, but also maize (also known as corn), rye, barley, and rice, amongst many other grasses and non-grain plants (including many Australian species of acacia). Flour is the key ingredient of bread, which is the staple food in many countries, and therefore the availability of adequate supplies of flour has often been a major economic and political issue. Flour can also be made from legumes and nuts, such as soy, peanuts, almonds, and other tree nuts.
Usually, the word "flour" used alone refers to wheat flour, which is one of the most important foods in European and American culture. The corresponding Spanish word "harina" normally refers to Maize flour - wheat flour is "harina de trigo". 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. However, certain individuals suffer from an intolerance to wheat gluten known as coeliac or celiac disease. Increased awareness of this disorder, as well as a rising belief in the benefits of a gluten-free diet for persons suffering certain other conditions, has led to an increased demand for bread and other products made with flours which do not contain gluten.
A coarser, somewhat granular preparation, 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, variously, "white" or "brown" if they have high gluten content, and "soft" or "weak flour" if gluten content is low. Hard flour, or "bread" flour, is high in gluten and so forms a certain toughness that 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 including bran, endosperm, and germ. A germ flour is made from the endosperm and germ, excluding the bran.
Whole-wheat flour is whole-grain wheat flour.
Bleached flour is flour that was subjected to flour bleaching agents in order to whiten it (freshly milled flour is yellowish) and give it more gluten-producing potential. Similar effect can be achieved by letting the flour slowly oxidize with oxygen in the air ("natural aging"); however this process is too slow to be commercially viable. Oxidizing agents are therefore employed, most commonly organic peroxides like acetone peroxide or benzoyl peroxide, nitrogen dioxide, or chlorine.
Bromated flour is flour with a maturing agent added. The agent's role is to help with developing gluten, a role similar to the flour bleaching agents. Bromate is usually used. Other choices are phosphates, ascorbic acid, and malted barley.
Cake flour is a finely milled flour made from soft wheat. It has very low gluten content, making it suitable for soft-textured cakes and cookies. Higher gluten content of other flours would make the cakes tough.
Graham flour is a special type of whole-wheat flour. The endosperm is finely ground, as in white flour, while the bran and germ are coarsely ground. Graham flour is uncommon outside of the USA. It is the basis of true graham crackers. Many graham crackers on the market are actually imitation grahams because they do not contain graham flour or even whole-wheat flour.
Pastry flour (also called cookie flour or cracker flour) has slightly higher gluten content than cake flour, but lower than all-purpose flour. It is suitable for fine, light-textured pastries.
Self-rising or self-raising flour is "white" wheat flour that is sold premixed with chemical leavening agents. It was invented by Henry Jones. Typical ratios are:
- U.S. customary:
- one cup flour
- 1 to 1½ teaspoon baking powder
- a pinch to ½ teaspoon salt
- 1 to 1½ teaspoon baking powder
- one cup flour
- 100 g flour
- 3 g baking powder
- 1 g or less salt
- 3 g baking powder
- 100 g flour
Wheat flour is also highly explosive, which is why in medieval flour mills there were not allowed to be any candles, lamps, or any other burning substance.
- Corn flour is popular in the Southern and Southwestern US and in Mexico. Coarse whole-grain corn flour is usually called corn meal. Corn meal that has been bleached with lye is called masa harina (see masa) and is used to make tortillas and tamales in Mexican cooking. Corn flour should never be confused with cornstarch, which is known as "cornflour" in British English.
- 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.
- Chestnut flour is popular in Corsica, the Périgord and Lunigiana. In Corsica, it is used to cook the local variety of polenta. In Italy, it is mainly used for desserts.
- Chickpea flour (also known as gram flour or besan) is of great importance in Indian cuisine, and in Italy, where it is used for the Ligurian farinata.
- 'Tang flour(not to be confused with the powdered beverage Tang) or wheat starch is a type of wheat flour used primarily in Chinese cooking for making the outer layer of dumplings and buns.
- Plain flour is another term for All Purpose flour, used in the UK.
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.