Gluten is a protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 composite found in foods processed from wheat

Wheat

Wheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...

 and related grain species, including barley

Barley

Barley is a major cereal grain, a member of the grass family. It serves as a major animal fodder, as a base malt for beer and certain distilled beverages, and as a component of various health foods...

 and rye

Rye

Rye is a grass grown extensively as a grain and as a forage crop. It is a member of the wheat tribe and is closely related to barley and wheat. Rye grain is used for flour, rye bread, rye beer, some whiskeys, some vodkas, and animal fodder...

. It gives elasticity

Viscoelasticity

Viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like honey, resist shear flow and strain linearly with time when a stress is applied. Elastic materials strain instantaneously when stretched and just...

 to dough

Dough

Dough is a paste made out of any cereals or leguminous crops by mixing flour with a small amount of water and/or other liquid. This process is a precursor to making a wide variety of foodstuffs, particularly breads and bread-based items , flatbreads, noodles, pastry, and similar items)...

, helping it to rise

Leavening agent

A leavening agent is any one of a number of substances used in doughs and batters that cause a foaming action which lightens and softens the finished product...

 and to keep its shape, and often giving the final product a chewy

Chewiness

Chewiness is the mouthfeel sensation of labored mastication due to sustained, elastic resistance from a foodstuff. Canonically chewy foods include caramel, rare steak, and such eponymously chewy items as chewing gum, Charleston Chew, and Chewy Granola Bars....

 texture.

Gluten is the composite of a gliadin

Gliadin

Gliadin is a glycoprotein present in wheat and several other cereals within the grass genus Triticum. Gliadins are prolamins and are separated on the basis of electrophoretic mobility and isoelectric focusing.- Types :...

and a glutelin

Glutelin

Glutelins proteins are soluble in dilute acids or bases, detergents, chaotropic, or reducing agents. In general, they are prolamin-like proteins in certain grass seeds. Glutenin is the most common glutelin, as it is found in wheat and is responsible for some of the refined baking properties in...

, which is conjoined with starch

Starch

Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...

 in the endosperm

Endosperm

Endosperm is the tissue produced inside the seeds of most flowering plants around the time of fertilization. It surrounds the embryo and provides nutrition in the form of starch, though it can also contain oils and protein. This makes endosperm an important source of nutrition in human diet...

 of various grass-related

Triticeae glutens

Triticeae glutens are seed storage proteins found in mature seeds of grass tribe Triticeae. Seed glutens of non-Triticeae plants have varieties of similar properties, but none singly can perform on a par with those of the Triticeae taxa, particularly the triticum species...

 grains

Cereal

Cereals are grasses cultivated for the edible components of their grain , composed of the endosperm, germ, and bran...

. The prolamin

Prolamin

Prolamins are a group of plant storage proteins having a high proline content and found in the seeds of cereal grains: wheat , barley , rye , corn , sorghum and as a minor protein, avenin in oats. They are characterised by a high glutamine and proline content and are generally soluble only in...

 and glutelin from wheat (gliadin

Gliadin

Gliadin is a glycoprotein present in wheat and several other cereals within the grass genus Triticum. Gliadins are prolamins and are separated on the basis of electrophoretic mobility and isoelectric focusing.- Types :...

, which is alcohol-soluble, and glutenin

Glutenin

Glutenin is the glutelin derived from wheat. Gluteninis a protein best known for its role, along with gliadin, in the creation of gluten with its disulfide inter- and intra-molecule links. Glutenin consists of 20% HMW subunits, which are relatively low in sulfur...

, which is only soluble in dilute acids or alkalis) compose about 80% of the protein contained in wheat seed

Seed

A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...

. Being insoluble

Solubility

Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on...

 in water, they can be purified by washing away the associated starch. Worldwide, gluten is a source of protein, both in foods prepared directly from sources containing it, and as an additive

Food additive

Food additives are substances added to food to preserve flavor or enhance its taste and appearance.Some additives have been used for centuries; for example, preserving food by pickling , salting, as with bacon, preserving sweets or using sulfur dioxide as in some wines...

 to foods otherwise low in protein

Low-protein diet

A low-protein diet is a diet in which people reduce their intake of protein. A low-protein diet is often prescribed to people with kidney or liver disease...

.

The seeds of most flowering plants have endosperms with stored protein to nourish embryonic plants

Plant embryogenesis

Plant embryogenesis is the process that produces a plant embryo from a fertilised ovule by asymmetric cell division and the differentiation of undifferentiated cells into tissues and organs. It occurs during seed development, when the single-celled zygote undergoes a programmed pattern of cell...

 during germination

Germination

Germination is the process in which a plant or fungus emerges from a seed or spore, respectively, and begins growth. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However the growth of a sporeling from a spore, for example the...

. True gluten, with gliadin and glutenin, is limited to certain members of the grass

Poaceae

The Poaceae is a large and nearly ubiquitous family of flowering plants. Members of this family are commonly called grasses, although the term "grass" is also applied to plants that are not in the Poaceae lineage, including the rushes and sedges...

 family. The stored proteins of maize

Maize

Maize known in many English-speaking countries as corn or mielie/mealie, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable...

 and rice

Rice

Rice is the seed of the monocot plants Oryza sativa or Oryza glaberrima . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East Asia, Southeast Asia, South Asia, the Middle East, and the West Indies...

 are sometimes called glutens, but their proteins differ from gluten.

Extraction

Gluten is extracted from flour

Flour

Flour is a powder which is made by grinding cereal grains, other seeds or roots . It is the main ingredient of bread, which is a staple food for many cultures, making the availability of adequate supplies of flour a major economic and political issue at various times throughout history...

 by kneading the flour, agglomerating the gluten into an elastic network, a dough

Dough

Dough is a paste made out of any cereals or leguminous crops by mixing flour with a small amount of water and/or other liquid. This process is a precursor to making a wide variety of foodstuffs, particularly breads and bread-based items , flatbreads, noodles, pastry, and similar items)...

, and then washing out the starch

Starch

Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...

. Starch granules disperse

Suspension (chemistry)

In chemistry, a suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometer. The internal phase is dispersed throughout the external phase through mechanical agitation, with the use of certain...

 in cold water, and the dispersed starch will be sedimented

Sedimentation

Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained, and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration...

 and dried. If a saline

Salt

In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...

 solution is used instead of water, a purer protein is obtained, with certain harmless impurities

Impurity

Impurities are substances inside a confined amount of liquid, gas, or solid, which differ from the chemical composition of the material or compound.Impurities are either naturally occurring or added during synthesis of a chemical or commercial product...

 going into solution with the starch. Where starch is the prime product, cold water is the favored solvent because the impurities stay with the gluten.

In home or play-dough cooking, a ball of wheat flour dough

Dough

Dough is a paste made out of any cereals or leguminous crops by mixing flour with a small amount of water and/or other liquid. This process is a precursor to making a wide variety of foodstuffs, particularly breads and bread-based items , flatbreads, noodles, pastry, and similar items)...

 is kneaded under water until the starch disperses out. In industrial production, a slurry

Slurry

A slurry is, in general, a thick suspension of solids in a liquid.-Examples of slurries:Examples of slurries include:* Lahars* A mixture of water and cement to form concrete* A mixture of water, gelling agent, and oxidizers used as an explosive...

 of wheat flour is kneaded vigorously by machinery until the gluten agglomerates into a mass. This mass is collected by centrifugation

Centrifugation

Centrifugation is a process that involves the use of the centrifugal force for the sedimentation of mixtures with a centrifuge, used in industry and in laboratory settings. More-dense components of the mixture migrate away from the axis of the centrifuge, while less-dense components of the mixture...

, then transported through several stages integrated in a continuous process. Approximately 65% of the water in the wet gluten is removed by means of a screw press

Screw press

A screw press is a type of machine press in which the ram is driven up and down by a screw. The screw shaft can be driven by a handle, or a wheel. It works by using a coarse screw to convert the rotation of the handle or drive-wheel into a small downward movement of greater force. The overhead...

; the remainder is sprayed through an atomizer nozzle

Atomizer nozzle

An atomizer nozzle is an aspirator nozzle for producing a fine spray of a liquid based on the Venturi effect.-Principle of operation :When a gas is injected under pressure through a tube with a decreasing section, it speeds up, generating a pressure drop at the narrowest point .The reduced...

 into a drying

Drying

Drying is a mass transfer process consisting of the removal of water or another solvent by evaporation from a solid, semi-solid or liquid. This process is often used as a final production step before selling or packaging products. To be considered "dried", the final product must be solid, in the...

 chamber, where it remains at an elevated temperature a short time to evaporate the water without denaturing the gluten. The process yields a flour-like powder with a 7% moisture content, which is air cooled and pneumatically

Pneumatics

Pneumatics is a branch of technology, which deals with the study and application of use of pressurized gas to effect mechanical motion.Pneumatic systems are extensively used in industry, where factories are commonly plumbed with compressed air or compressed inert gases...

 transported to a receiving vessel. In the final step, the collected gluten is sifted

Sieve

A sieve, or sifter, separates wanted elements from unwanted material using a woven screen such as a mesh or net. However, in cooking, especially with flour, a sifter is used to aerate the substance, among other things. A strainer is a type of sieve typically used to separate a solid from a liquid...

 and milled

Mill (grinding)

A grinding mill is a unit operation designed to break a solid material into smaller pieces. There are many different types of grinding mills and many types of materials processed in them. Historically mills were powered by hand , working animal , wind or water...

 to produce a uniform product.

Uses

Bread products

Gluten forms when glutenin molecule

Molecule

A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

s cross-link to form a sub-microscopic network attached to gliadin, which contributes viscosity

Viscosity

Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

 (thickness) and extensibility to the mix. If this dough is leavened

Leavening agent

A leavening agent is any one of a number of substances used in doughs and batters that cause a foaming action which lightens and softens the finished product...

 with sugar

Sugar

Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...

, fermentation

Fermentation (food)

Fermentation in food processing typically is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions. Fermentation in simple terms is the chemical conversion of sugars into ethanol...

 produces carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 bubbles, which, trapped by the gluten network, cause the dough to rise. Baking

Baking

Baking is the technique of prolonged cooking of food by dry heat acting by convection, and not by radiation, normally in an oven, but also in hot ashes, or on hot stones. It is primarily used for the preparation of bread, cakes, pastries and pies, tarts, quiches, cookies and crackers. Such items...

 coagulates

Denaturation (biochemistry)

Denaturation is a process in which proteins or nucleic acids lose their tertiary structure and secondary structure by application of some external stress or compound, such as a strong acid or base, a concentrated inorganic salt, an organic solvent , or heat...

 the gluten, which, along with starch, stabilizes the shape of the final product. Gluten content has been implicated as a factor in the staling

Staling

Staling, or "going stale", is a chemical and physical process in bread and other foods that reduces their palatability. Stale bread is dry and leathery.-Mechanism and effects:...

 of bread, possibly because it binds water through hydration.

The development of gluten (i.e., enhancing its elasticity) affects the texture of the baked goods. Gluten's attainable elasticity is proportional to its content of glutenins with low molecular weights as this portion contains the preponderance of the sulfur atoms responsible for the cross-linking in the network.
More refining (of the gluten) leads to chewier products such as pizza

Pizza

Pizza is an oven-baked, flat, disc-shaped bread typically topped with a tomato sauce, cheese and various toppings.Originating in Italy, from the Neapolitan cuisine, the dish has become popular in many parts of the world. An establishment that makes and sells pizzas is called a "pizzeria"...

 and bagels, while less refining yields tender baked goods such as pastry products. Generally, bread

Bread

Bread is a staple food prepared by cooking a dough of flour and water and often additional ingredients. Doughs are usually baked, but in some cuisines breads are steamed , fried , or baked on an unoiled frying pan . It may be leavened or unleavened...

 flour

Flour

Flour is a powder which is made by grinding cereal grains, other seeds or roots . It is the main ingredient of bread, which is a staple food for many cultures, making the availability of adequate supplies of flour a major economic and political issue at various times throughout history...

s are high in gluten (hard wheat); pastry

Pastry

Pastry is the name given to various kinds of baked products made from ingredients such as flour, sugar, milk, butter, shortening, baking powder and/or eggs. Small cakes, tarts and other sweet baked products are called "pastries."...

 flours have a lower gluten content. Kneading

Kneading

Kneading is a process in the making of bread or pasta dough, used to mix together the ingredients and add strength to the final product. Its importance lies in the mixing of flour with water. When these two ingredients are combined and kneaded, the gliadin and glutenin proteins in the flour expand...

 promotes the formation of gluten strands and cross-links, creating baked product that is chewier in proportion to the length of kneading. An increased moisture content in the dough enhances gluten development, and very wet doughs left to rise for a long time require no kneading (see no-knead bread

No-knead bread

No-knead bread is a method of bread baking that uses a very long rising time instead of kneading to form the gluten strands that give the bread its texture. It is characterized by a low yeast content and a very wet dough...

). Shortening

Shortening

Shortening is any fat that is solid at room temperature and used to make crumbly pastry. The reason it is called shortening is because it prevents cross-linkage between gluten molecules. Cross linking is what causes doughs to be sticky. Seeing as cake is not meant to be sticky, shortening is used...

 inhibits formation of cross-links and is used, along with diminished water and less kneading, when a tender and flaky product, such as a pie crust, is desired.

The strength and elasticity of gluten in flour is measured in the baking industry using a farinograph

Farinograph

In Baking, a Farinograph measures specific properties of flour. It was first developed and launched in 1928 Brabender History. The Farinograph is used as a tool to measure shear and viscosity of a mixture of flour and water. The primary units of the farinograph are Brabender Units, an arbitrary...

. This gives the baker a measurement of quality for different varieties of flours in developing recipes for various baked goods.

Added gluten

Gluten, when dried and milled to a powder and added to ordinary flour dough, improves a dough's ability to rise and increases the bread's structural stability and chewiness. Gluten-added dough must be worked vigorously to induce it to rise to its full capacity; an automatic bread machine

Bread machine

A bread making machine or bread maker is a home appliance for baking bread. It consists of a bread pan with a paddle mounted in the center of a small special-purpose oven, with a control panel...

 or food processor

Food processor

A food processor is a kitchen appliance used to facilitate various repetitive tasks in the process of preparation of food. Today, the term almost always refers to an electric-motor-driven appliance, although there are some manual devices also referred to as "food processors".Food processors are...

 may be required for kneading

Kneading

Kneading is a process in the making of bread or pasta dough, used to mix together the ingredients and add strength to the final product. Its importance lies in the mixing of flour with water. When these two ingredients are combined and kneaded, the gliadin and glutenin proteins in the flour expand...

. The added gluten provides supplemental protein to products with low or nonexistent protein levels.

Imitation meats

Gluten, especially wheat gluten

Wheat gluten (food)

Wheat gluten, also called seitan , wheat meat, mock duck, gluten meat, or simply gluten, is a food made from the gluten of wheat...

, is often the basis for imitation meats

Meat analogue

A meat analogue, also called a meat substitute, mock meat, faux meat, or imitation meat, approximates the aesthetic qualities and/or chemical characteristics of specific types of meat...

 resembling chicken

Chicken

The chicken is a domesticated fowl, a subspecies of the Red Junglefowl. As one of the most common and widespread domestic animals, and with a population of more than 24 billion in 2003, there are more chickens in the world than any other species of bird...

, duck

Duck

Duck is the common name for a large number of species in the Anatidae family of birds, which also includes swans and geese. The ducks are divided among several subfamilies in the Anatidae family; they do not represent a monophyletic group but a form taxon, since swans and geese are not considered...

 (mock duck

Mock duck

Mock duck is a gluten-based vegetarian food. It is generally made from wheat gluten and is thus high in protein. Its distinctive flavor and artificial "plucked duck" texture distinguish it from other forms of commercially available gluten products. Mock duck can be found in some Chinese grocery...

), fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

, pork

Pork

Pork is the culinary name for meat from the domestic pig , which is eaten in many countries. It is one of the most commonly consumed meats worldwide, with evidence of pig husbandry dating back to 5000 BC....

 and beef

Beef

Beef is the culinary name for meat from bovines, especially domestic cattle. Beef can be harvested from cows, bulls, heifers or steers. It is one of the principal meats used in the cuisine of the Middle East , Australia, Argentina, Brazil, Europe and the United States, and is also important in...

. When cooked in broth

Broth

Broth is a liquid food preparation, typically consisting of either water or an already flavored stock, in which bones, meat, fish, cereal grains, or vegetables have been simmered. Broth is used as a basis for other edible liquids such as soup, gravy, or sauce. It can be eaten alone or with garnish...

, gluten absorbs some of the surrounding liquid (including the taste) and becomes firm to the bite.

Added to other foods

The "Codex Alimentarius

Codex Alimentarius

The Codex Alimentarius is a collection of internationally recognized standards, codes of practice, guidelines and other recommendations relating to foods, food production and food safety. Its name derives from the Codex Alimentarius Austriacus...

" international standard

International standard

International standards are standards developed by international standards organizations. International standards are available for consideration and use, worldwide...

s for food labeling

Food labelling

Food labelling may refer to:*Packaging and labeling in general, as applied to food*Nutrition facts label as required by legislation in some countries- See also :* Food labeling regulations*Refrigerate after opening*Shake well*Standard of identity...

 has a standard relating to the labeling of products as "gluten-free", but this standard does not apply to foods that "...in their normal form do not contain gluten." Gluten is used as a stabilizing agent

Food additive

Food additives are substances added to food to preserve flavor or enhance its taste and appearance.Some additives have been used for centuries; for example, preserving food by pickling , salting, as with bacon, preserving sweets or using sulfur dioxide as in some wines...

 in products like ice cream

Ice cream

Ice cream is a frozen dessert usually made from dairy products, such as milk and cream, and often combined with fruits or other ingredients and flavours. Most varieties contain sugar, although some are made with other sweeteners...

 and ketchup

Ketchup

Ketchup is a sweet-and-tangy condiment typically made from tomatoes, vinegar, sugar or high-fructose corn syrup and an assortment of...

, where it might be unexpected. Foods of this kind present a problem because the hidden gluten constitutes a hazard for people with celiac disease: In the United States, at least, gluten might not be listed on the labels of such foods because the U.S. Food and Drug Administration

Food and Drug Administration

The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...

 has classified gluten as GRAS (generally recognized as safe

Generally recognized as safe

Generally recognized as safe is an American Food and Drug Administration designation that a chemical or substance added to food is considered safe by experts, and so is exempted from the usual Federal Food, Drug, and Cosmetic Act food additive tolerance requirements.-History:On January 1, 1958,...

). Requirements for proper labeling are being formulated by the USDA. In the United Kingdom

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

, only cereals currently must be labeled, while labeling of other products is voluntary.

Adverse reactions

Between 0.5 and 1.0 percent of people in the United States are sensitive to gluten due to Celiac disease. Celiac disease constitutes an abnormal immune reaction to partially digested gliadin. It probably occurs with comparable frequencies among all wheat-eating populations in the world. Certain allergies and neuropathies are also caused by gluten consumption and inhalation. In some instances what is known as cross contamination can occur without the person even being aware that they are ingesting gluten. Known examples occur when people share silverware or other eating instruments. There have also been confirmed reports of cross contamination through oral sex. Doctors have warned that this is possible for as many as 30 days after a person injests gluten containing products. People known to be allergic to gluten often cite this as an area of "extreme frustration". Wheat allergy

Wheat allergy

Wheat allergy is a food allergy, but can also be a contact allergy resulting from occupational exposure. Like all allergies wheat allergy involves IgE and mast cell response. Typically the allergy is limited to the seed storage proteins of wheat, some reactions are restricted to wheat proteins,...

and celiac disease are different disorders.