Flour is a powder made by grinding raw grains, roots, beans, nuts, or seeds. It is used to make many different foods. Cereal flour is the main ingredient of bread, which is a staple food for most cultures. Wheat flour is one of the most important ingredients in Oceanic, European, South American, North American, Middle Eastern, North Indian and North African cultures, and is the defining ingredient in their styles of breads and pastries.

Wheat is the most common base for flour.

Corn flour has been important in Mesoamerican cuisine since ancient times and remains a staple in the Americas. Rye flour is a constituent of bread in central Europe.

Cereal flour consists either of the endosperm, germ, and bran together (whole-grain flour) or of the endosperm alone (refined flour). Meal is either differentiable from flour as having slightly coarser particle size (degree of comminution) or is synonymous with flour; the word is used both ways. For example, the word cornmeal often connotes a grittier texture whereas corn flour connotes fine powder, although there is no codified dividing line.

The English word "flour" is originally a variant of the word "flower" and both words derive from the Old French fleur or flour, which had the literal meaning "blossom", and a figurative meaning "the finest". The phrase "fleur de farine" meant "the finest part of the meal", since flour resulted from the elimination of coarse and unwanted matter from the grain during milling.^[1]

The earliest archaeological evidence for wheat seeds crushed between simple millstones to make flour dates to 6000 BC.^[2] The Romans were the first to grind seeds on cone mills. In 1879, at the beginning of the Industrial Era, the first steam mill was erected in London.^[3] In the 1930s, some flour began to be enriched with iron, niacin, thiamine and riboflavin. In the 1940s, mills started to enrich flour and folic acid was added to the list in the 1990s.

An important problem of the industrial revolution was the preservation of flour. Transportation distances and a relatively slow distribution system collided with natural shelf life. The reason for the limited shelf life is the fatty acids of the germ, which react from the moment they are exposed to oxygen. This occurs when grain is milled; the fatty acids oxidize and flour starts to become rancid. Depending on climate and grain quality, this process takes six to nine months. In the late 19th century, this process was too short for an industrial production and distribution cycle. As vitamins, micronutrients and amino acids were completely or relatively unknown in the late 19th century, removing the germ was an effective solution. Without the germ, flour cannot become rancid. Degermed flour became standard. Degermation started in densely populated areas and took approximately one generation to reach the countryside. Heat-processed flour is flour where the germ is first separated from the endosperm and bran, then processed with steam, dry heat or microwave and blended into flour again.^[4]

The FDA has been advised by several cookie dough manufacturers that they have implemented the use of heat-treated flour for their "ready-to-bake cookie dough" products to reduce the risk of E. coli bacterial contamination.^[5]

Milling of flour is accomplished by grinding grain between stones or steel wheels.^[6] 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.

Roller mills 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^[7] and windmill. These terms are now applied more broadly to uses of water and wind power for purposes other than milling.^[8] More recently, the Unifine mill, an impact-type mill, was developed in the mid-20th century.

Home users have begun grinding their own flour from organic wheat berries on a variety of electric flour mills.

The grinding process is not much different from grinding coffee but the mills are larger.

This provides fresh flour with the benefits of wheat germ and fiber without spoilage.

Modern farm equipment allows livestock farmers to do some or all of their own milling when it comes time to convert their own grain crops to coarse meal for livestock feed. This capability is economically important because the profit margins are often thin enough in commercial farming that saving expenses is vital to staying in business.

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 (known as plain outside North America), self-rising flour (known as self-raising outside North America), 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.^[9]

"Bleached flour" is any refined flour with a whitening agent added.

"Refined flour" has had the germ and bran removed and is typically referred to as "white flour".

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 US are:

Some other chemicals used as flour treatment agents to modify color and baking properties include:

Common preservatives in commercial flour include:

Cake flour in particular is nearly always chlorinated.

At least one flour labeled "unbleached cake flour blend" (marketed by King Arthur Flour) 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 blended with all-purpose flour is commonly substituted for cake flour when the latter is unavailable). The end product, however, is denser than would result from lower-protein, chlorinated cake flour.

All bleaching and maturing agents (with the possible exception of ascorbic acid) have been banned in the United Kingdom.^[11]

Bromination of flour in the US has fallen out of favor, and while it is not yet actually banned anywhere, few retail flours available to the home baker are bromated anymore.

Many varieties of flour packaged specifically for commercial bakeries are still bromated.

Retail bleached flour marketed to the home baker is now treated mostly with either peroxidation or chlorine gas.

Current information from Pillsbury is that their varieties of bleached flour are treated both with benzoyl peroxide and chlorine gas.

Gold Medal states that their bleached flour is treated either with benzoyl peroxide or chlorine gas, but no way exists to tell which process has been used when buying the flour at the grocery store.

During the process of making flour nutrients are lost.

Some of these nutrients may be replaced during refining – the result is enriched flour.

Cake flour is the lowest in gluten protein content, with 6-7%^[12] (5-8% from second source^[13]) protein to produce minimal binding so "the cake crumbles" easily.

Pastry flour has the second-lowest gluten protein content, with 7.5-9.5%^[12] (8-9% from second source^[13]) protein to hold together with a bit more strength than cakes, but still produce flaky crusts rather than hard or crisp ones.

All-purpose, or "AP flour", or plain flour is medium in gluten protein content at 9.5-11.5%^[12](10-12% from second source^[13]) protein content. It has adequate protein content for many bread and pizza bases, though bread flour and special 00 grade Italian flour are often preferred for these purposes, respectively, especially by artisan bakers. Some biscuits are also prepared using this type of flour. "Plain" refers not only to AP flour's middling gluten content but also to its lack of any added leavening agent (as in self-rising flour).

Bread flour, or strong flour is high in gluten protein, with 11.5-13.5%^[12](12-14% from second source^[13]) protein. The increased protein binds to the flour to entrap carbon dioxide released by the yeast fermentation process, resulting in a stronger rise and more chewy crumb. Bread flour may be made with a hard spring wheat.

Hard is a general term for flours with high gluten protein content, commonly refers to extra strong flour, with 13.5-16%^[12]*The%20Bread%20Baker's%20Apprent]]*The%20Bread%20Baker's%20Apprent]]*The%20Bread%20Baker's%20Apprent]]*The%20Bread%20Baker's%20Apprent]]*or 14-15% from some sources) protein (16% is a theoretically possible protein content

Gluten flour is refined gluten protein, or a theoretical 100% protein (though practical refining never achieves a full 100%).

It is used to strengthen flour as needed.

For example, adding approximately one teaspoon per cup of AP flour gives the resulting mix the protein content of bread flour.

It is commonly added to whole grain flour recipes to overcome the tendency of greater fiber content to interfere with gluten development, needed to give the bread better rising (gas holding) qualities and chew.

Unbleached flour is simply flour that has not undergone bleaching and therefore does not have the color of "white" flour.

An example is Graham flour, whose namesake, Sylvester Graham, was against using bleaching agents, which he considered unhealthy.

Leavening agents are used with some varieties of flour,^[14] especially those with significant gluten content, to produce lighter and softer baked products by embedding small gas bubbles. Self-raising (or self-rising) flour is sold mixed with chemical leavening agents. The added ingredients are evenly distributed throughout the flour, which aids a consistent rise in baked goods. This flour is generally used for preparing sponge cakes, scones, muffins, etc. It was invented by Henry Jones and patented in 1845. Plain flour can be used to make a type of self-raising flour, although the flour will be coarser. Self-raising flour is typically composed of (or can be made from):

Wheat is the grain most commonly used to make flour.

Certain varieties may be referred to as "clean" or "white".

Flours contain differing levels of the protein gluten. "Strong flour" or "hard flour" has a higher gluten content than "weak" or "soft" flour. "Brown" and wholemeal flours may be made of hard or soft wheat.

When gluten-free flours are free from contamination with gluten, they are suitable for people with gluten-related disorders, such as coeliac disease, non-celiac gluten sensitivity or wheat allergy sufferers, among others.^{[16][17][18][19]} Contamination with gluten-containing cereals can occur during grain harvesting, transporting, milling, storing, processing, handling and/or cooking.^[19][20][21]

Flour also can be made from soybeans, arrowroot, taro, cattails, acorns, manioc, quinoa, and other non-cereal foodstuffs.

In some markets, the different available flour varieties are labeled according to the ash mass that remains after a sample is incinerated in a laboratory oven (typically at 550 °C or 900 °C, see international standards ISO 2171 and ICC 104/1 ^[36] ). This is an easily verified indicator for the fraction of the whole grain remains 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 with an extraction rate of 50–60% leaves about 0.4 g.

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 way for comparing the extraction rates of different available flour types.

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:

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.

There is no French type corresponding to the lowest ash residue in the table.

The closest is French Type 45.

Also there is no Chinese name corresponding to the highest ash residue in the table.Usually

such product are imported from Japan and the Japanese name Zenryufun(全粒粉) is used.

It is possible to determine ash content from some US manufacturers.

However, US measurements are based on wheat with a 14% moisture content.

Thus, a US flour with 0.48% ash would approximate a French Type 55.

Other measurable properties of flour as used in baking can be determined using a variety of specialized instruments, such as the farinograph.

Flour dust suspended in air is explosive—as is any mixture of a finely powdered flammable substance with air^[31] (see dust explosion). Some devastating explosions have occurred at flour mills, including an explosion in 1878 at the Washburn "A" Mill in Minneapolis which killed 22 people.^[32]

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 thickening gravy and sauces. It can also be used as an ingredient in papier-mâché glue.^[33]

Cornstarch is a principal ingredient used to thicken many puddings or desserts, and is the main ingredient in packaged custard.