An ingredient used in many foods, flour is a fine powder made by grinding cereals or other edible starchy plant seeds suitable for grinding. It is most commonly made from wheat—the word "flour" used without qualification implies wheatflour—but also maize (now called corn in many parts of the Western Hemisphere), rye, barley, and rice, amongst many other grasses and non-grain plants (including buckwheat, grain amaranths and many Australian species of acacia). Ground legumes and nuts, such as soy, peanuts, almonds, and other tree nuts, are also called flours. The same substances ground more coarsely are called "meal" instead of "flour".

Flour is the key ingredient of bread, which is the staple food in most countries, and therefore the availability of adequate supplies of flour has often been a major economic and political issue.

Flour always contains a high proportion of starches, which are complex carbohydrates also known as polysaccharides.

Wheat flour is one of the most important foods in European and American culture, and is the defining ingredient in most types of breads and pastries. Regulations in many countries require that wheat flour be enriched to replace nutrients lost in the production of refined flour.

When wheat flour is mixed with water gluten, a complex protein, develops. Gluten 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 an aerated final product with a soft texture, desirable for breads, cakes and the like.

Some people suffer from an intolerance to 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, pasta, and other products made with flours that do not contain gluten.

There are some exceptions; in the UK, cornflour is the white, powdered starch of the maize grain, not ground maize.

Types of flour

Wheat flour

Protein
5-8%	Cake Flour
8-10%	Pastry Flour
10-11.5%	All-Purpose Flour
11-13%	Bread Flour
14% and up	High-Gluten Flour

Much more wheat flour is produced than any other flour.

Wheat varieties are called "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, with 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.

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 or Wholemeal 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.

Wheat flour is highly explosive when airborne. The most benign cases occur in classroom flour bombs; more sinister applications include fuel-air explosives improvised by so-called "anarchists" or terrorists. In medieval flour mills, candles, lamps, or other sources of fire were forbidden.

All-purpose or plain flour

This flour is a blended wheat flour with an intermediate gluten level which is marketed as an acceptable compromise for most household baking needs.

Bleached flour

Treated with flour bleaching agents to whiten it (freshly milled flour is yellowish) and to give it more gluten-producing potential. Oxidizing agents are usually employed, most commonly organic peroxides like acetone peroxide or benzoyl peroxide, nitrogen dioxide, or chlorine. A similar effect can be achieved by letting the flour slowly oxidize with oxygen in the air ("natural aging") for approximately 10 days; however, this process is more expensive due to the time required. [1]

Bromated flour

This is a 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. Bromated flour has been banned in much of the world, but remains available in the United States.

Cake flour

This is a finely milled flour made from soft wheat. It has very low gluten content, making it suitable for soft-textured cakes and cookies. The higher gluten content of other flours would make the cakes tough.

Graham flour 

This 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 and the cities of Romania. 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 or cookie flour or cracker flour

This 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

This is "white" wheat flour or wholemeal flour that is sold premixed with chemical leavening agents. It was invented by Henry Jones. It can also be substituted by Maida when cooking under the Indian Cuisine. Typical ratios are:

U.S. customary:

• one cup flour
• 1 to 1½ teaspoon baking powder
• a pinch to ½ teaspoon salt

Metric:

• 100 g flour
• 3 g baking powder
• 1 g or less salt

Durum or semolina flour

This flour is made of durum wheat. It has the highest protein content, and it is an important component of nearly all noodles and pastas. It is also commonly used to make Indian flatbreads.

In Britain, many flours go by names different than those from America. Some American flours and British equivalents include:

• Cake and pastry flour = soft flour
• All-purpose flour = plain flour
• Bread flour = strong flour, hard flour
• Self-rising flour = self-raising flour
• Whole-wheat flour = wholemeal flour

Other flours

• Corn (maize) 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.

• Noodle flour is special blend of flour used for the making of Asian style noodles.

• Buckwheat flour is used as an ingredient in many pancakes in the United States. In Japan, it is used to make a popular noodle called Soba. In Russia, buckwheat flour is added to the batter for pancakes called blinis which are frequently eaten with caviar. Buckwheat flour is also used to make Breton crepes called galettes.

• 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.

• Teff flour is made from the grain teff, and is of considerable importance in eastern Africa (particularly around the horn of Africa). Notably, it is the chief ingredient in the bread injera, an important component of Ethiopian cuisine.

• Atta flour is a wheat flour which is important in Indian cuisine, used for a range of breads such as roti and chapati.

• 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.

• Glutinous rice flour or sticky rice flour, used in east and southeast Asian cuisines for making tangyuan etc.

• Peasemeal or pea flour is a flour produced from roasted and pulverized yellow field peas.

• Bean flour is a flour produced from pulverized dried or ripe beans.

• Potato flour is obtained by grinding the tubers to a pulp and removing the fibre by water-washings. The dried product consists chiefly of starch, but also contains some protein. Potato flour is used as a thickening agent. When heated to boiling, food added with a suspension of potato flour in water thickens quickly. Because the flour is made from neither grain nor legume, it is used as substitute for wheat flour in cooking by Jews during Passover, when grains are not eaten.

• Amaranth flour is a flour produced from ground Amaranth grain. It was commonly used in pre-Columbian meso-American cuisine. It is becoming more and more available in specialty food shops.

• Nut flours are ground from oily nuts--most commonly almonds and hazelnuts--and are used instead of or in addition to wheat flour to produce more dry and flavorful pastries and cakes. Cakes made with nut flours are usually called tortes and most originated in Central Europe, in countries such as Hungary and Austria.

Flour can also be made from buckwheat, soy beans, arrowroot, taro, cattails, acorns, peas, beans, and other non-grain foodstuffs.

Flour type numbers

In some markets, the different available flour varieties are labeled according to the ash mass ("mineral content") that remains after a sample was incinerated in a laboratory oven (typically at 550 °C or 900 °C, see international standards ISO 2171 and ICC 104/1). This is an easy to verify indicator for the fraction of the whole grain that ended up in the flour, because the mineral content of the starchy endosperm is much lower than that of the outer parts of the grain. Flour made from all parts of the grain (extraction rate: 100%) leaves about 2 g ash or more per 100 g dry flour. Plain white flour (extraction rate: 50-60%) leaves only about 0.4 g.

• German flour type numbers (Mehltype) indicate the amount of ash (measured in milligrams) obtained from 100 g of the dry mass of this flour. Standard wheat flours (defined in DIN 10355) range from type 405 for normal white wheat flour for baking, to strong bread flour types 550, 650, 812, and the darker types 1050 and 1600 for wholegrain breads.

• French flour type numbers (type de farine) are a factor 10 smaller than those used in Germany, because they indicate the ash content (in milligrams) per 10 g flour. Type 55 is the standard, hard-wheat white flour for baking, including puff pastries ("pâte feuilletée"). Type 45 is often called pastry flour, but is generally from a softer wheat. Types 65, 80, and 110 are strong bread flours of increasing darkness, and type 150 is a wholemeal flour.

In the United States and the United Kingdom, no numbered standardized flour types are defined, and the ash mass is only rarely given on the label by flour manufacturers. However, the legally required standard nutrition label specifies the protein content of the flour, which is also a suitable way for comparing the extraction rates of different available flour types.

It is possible to find out ash content from some US manufacturers. However, US measurements are based on wheat with a 14% moisture content. Thus, a US flour with .48 ash would approximate a French Type 55.

In general, as the extraction rate of the flour increases, so do both the protein and the ash content. However, as the extraction rate approaches 100% (whole meal), the protein content drops slightly, while the ash content continues to rise.

The following table shows some typical examples of how protein and ash content relate to each other in wheat flour:

Ash	Protein	Wheat flour type
		US	German	French
~0.4%	~9%	pastry flour	405	45
~0.55%	~11%	all-purpose flour	550	55
~0.8%	~14%	high gluten flour	812	80
~1%	~15%	first clear flour	1050	110
>1.5%	~13%	white whole wheat	1600	150

This table is only a rough guideline for converting bread recipes. Since the American flour types are not standardized, the numbers may differ between manufacturers.

Flour production

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 horizontially with the grain in between. Many small appliance mills are 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,^[1] see Lycopodium. Some devastating and fatal explosions have occurred at flour mills, including an explosion in 1878 at the Washburn "A" Mill in Minneapolis, the largest flour mill in the United States at the time.^[2]

History

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.

Flour products

Bread, pasta, crackers, many cakes, and 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 or desserts.

External links

• Grain and wheat flour
• Cooking For Engineers - Kitchen Notes: Wheat Flour
• h2g2 entry on Bread Flour
• British Nutrition Foundation - Flour Information

References

1. ^ Williamson, George (06-02-2002). Introduction to Dust Explosions. Retrieved on 2006-10-29.
2. ^ Washburn ‘A’ Mill Explosion. Minnesota Historical Society Library History Topics. Retrieved on 2006-10-29.

• The Bread and Flour Regulations 1998, United Kingdom.
• This article incorporates text from the public domain 1911 edition of The Grocer's Encyclopedia.bar:Mäihzh-yue:麪粉

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