Flour is a powder made of cereal grains. It is the key ingredient of bread, which is a staple food in many countries, and therefore the availability of adequate supplies of flour has often been a major economic and political issue. Wheat flour is one of the most important foods in European and North American culture, and is the defining ingredient in most European styles of breads and pastries. Regulations in many countries require that wheat flour be enriched to replace nutrients lost in the production of refined flour.
Flour contains a high proportion of starches, which are complex carbohydrates also known as polysaccharides. Wheat, and some other flours, also contain proteins called gluten. When dough made with wheat flour is kneaded, the gluten molecules cross-link to form a sub-microscopic network that gives the dough an elastic structure. This 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.
Types of flour
Much more wheat
flour is produced than any other flour.
Wheat varieties are called "clean," "white," or "brown" if they have high gluten content, and they are called "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 fruit) used in flour—the endosperm or starchy part, the germ or protein part, and the bran or fibre 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.
All-purpose or plain 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 is 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.
Bromated flour 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,
as bromate is a suspected carcinogen,
but remains available in the United States.
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. The higher gluten content of other flours would make the cakes tough. Related to cake flour are masa harina (from maize), maida flour (from wheat or tapioca), and pure starches.
Pastry flour or 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.
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 and Europe. 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.
Self-rising or self-raising flour is flour ("white" wheat flour or wholemeal) that is sold premixed with chemical leavening agents. It was invented by Henry Jones. Typical ratios are the following:
- *a pinch to ½ teaspoon salt
- *100 g flour
- *3 g baking powder
- *1 g or less salt
Sprouted Flour is a new flour that is produced from whole grains that have been sprouted back into an alive plant and then dried prior to milling. Currently, spouted whole grain hard and soft wheat and sprouted whole grain spelt flours are available in the United States. Sprouted flours may be substituted one for one for most all-purpose flours in recipes. Because the whole grains have been sprouted the flours may be easier to digest.
- Corn (maize) flour is popular in the Southern and Southwestern US, Mexico, and Punjab regions of India and Pakistan. 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.
- Atta flour is a whole-grain wheat flour important in Indian cuisine, used for a range of breads such as roti, naan and chapati.
- 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.
- Tapioca flour, produced from the root of the cassava plant, is used to make breads, pancakes, tapioca pudding, a savoury porridge called fufu in Africa, and is used as a starch.
- Rice flour
- Glutinous rice flour or sticky rice flour, used in east and southeast Asian cuisines for making tangyuan etc.
- Brown 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 crêpes bretonnes in Brittany.
- Chestnut flour is popular in Corsica, the Périgord and Lunigianafor breads, cakes and pastas. It is the original ingredient for “polenta”, still used as such in Corsica and other Mediterranean locations. Chestnut bread keeps fresh for as long as two weeks.. 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.
- 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. It is also used in Vietnamese cuisine, where it is called bột lọc trong.
- 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 starch 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.
- Chuño flour made from dried potatoes in various countries of South America
- 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 speciality food shops.
- Nut flours are grated 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.
- Sprouted whole grain Wheat flour is a flour produced from the whole wheat grain that has been sprouted back into a living plant and then dried prior to milling. It can be substituted one for one for most all-purpose flours in baking recipes.
- Sprouted whole grain Spelt flour is a flour produced from the whole spelt grain that has been sprouted back into a living plant and then dried prior to milling. It can be substituted one for one for most all-purpose flours in baking recipes.
Flour can also be made from soy beans, peanuts, arrowroot, taro, cattails, acorns, quinoa and other non-cereal 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:
||Wheat flour type
|| French |
|| pastry flour
|| 45 |
|| all-purpose flour
|| 55 |
|| high gluten flour
|| 80 |
|| first clear flour
|| 110 |
|| white whole wheat
|| 150 |
This table is only a rough guideline for converting bread recipes. Since flour types are not standardized in many countries, the numbers may differ between manufacturers.
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.
Flour dust suspended in air is explosive, as is any mixture of a finely powdered flammable substance with air, see Lycopodium
. In medieval flour mills, candles, lamps, or other sources of fire were forbidden. Some devastating and fatal explosions have occurred at flour mills, including an explosion in 1878 at the Washburn "A" Mill
, the largest flour mill in the United States at the time.
, many cakes
, and many other foods are made using flour. Wheat flour is also used to make a roux
as a base for gravy
. 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