Gluten is one of the most important constituents of the varieties of corn used as food. It is obtained by mixing flour with water, and thus forming a paste or dough. This paste is placed in a bag of fine linen, and kneaded in water, which must be repeatedly changed till it ceases to assume a milky appearance. A gray, tenacious, viscous, tasteless substance, having the appearance of bird-lime, is left in the bag. This substance consists mainly of gluten, mixed with traces of bran starch and of oily matter. The gluten thus obtained from wheat and from rye is far more tenacious than that which is obtained from the other cereals, and it is the great tenacity of this constituent that especially fits these flours for conversion into bread. It is found by analysis that the proportion of gluten (16 per cent.) contained in wheat grown in Algeria and other hot countries is considerably higher than in wheat grown in England (10.7 per cent.), or still colder countries; the proportion in the wheat of the United States seems to vary from 9.85 to as much as 15.25 per cent.; and the hard, thin-skinned wheats contain more of this ingredient than the softer varieties of the grain.
Gluten in a moist state rapidly putrefies, the mass acquiring the smell of decaying cheese; but when dry it forms a hard, brownish, horny-looking mass, that does not very readily decompose. On treating gluten with hot alcohol, we find that it resolves itself into at least two distinct substances, one of which is soluble, and the other insoluble in that fluid. The insoluble portion—vegetable fibrin—is a gray, tough, elastic substance, insoluble in water or in ether, but readily soluble in dilute alkalies, from which it is precipitated by neutralisation with acetic acid. The soluble portion is in part precipitated from the alcohol on cooling, in the form of flakes, which have the composition and properties of casein—a vegetable casein; while a third substance, gliadin, remains in solution, giving to the alcohol a syrupy consistence, but separating on the addition of water, as a white substance resembling albumen. All these constituents of gluten contain carbon, hydrogen, nitrogen, oxygen, and sulphur, in much the same proportion as the animal albuminates or protein bodies, and they all doubtless belong to the flesh-forming group of foods.
The action of gluten in the manufacture of bread is probably a double one; it induces, by constant action, an alteration of the starch, and subsequent fermentation, while by its tenacity it prevents the escape of carbonic acid gas. See BREAD.