Gluten, Or Vegetable Fibrine a tough elastic substance, named from its adhesive glue-like property, an ingredient in wheat especially, and in smaller proportion in most of the cerealia and in some leguminous plants. When wheat flour is well kneaded upon a sieve under a stream of water, the starch is removed in suspension in the water, and the soluble dextrine and sugar are washed away, and the gluten remains behind. This was supposed by Beccaria, who first noticed it, to be a distinct principle; but it is found still to retain a little starch, and other ingredients are separated from it according to their different reactions when treated with boiling alcohol. The pure vegetable fibrine is then found to constitute about 72 per cent. of the original gluten, while an albuminous substance called gliadine, vegetable caseine, and a vegetable oil make up the remainder. Gluten from rye flour contains very little of the tenacious ingredient, gliadine; and other grains furnish gluten of variable proportions of its ingredients. It is gluten which gives to the dough of wheat flour its peculiar tenacity, and it is owing to this that the escape of carbonic acid gas is arrested in the fermentation of wheat bread, and the product is consequently lighter and more spongy than other bread.
Macaroni and vermicelli are preparations of gluten, and the flour of the south of Europe is said to be peculiarly adapted for this manufacture, as it generally contains a considerably larger proportion of gluten than that grown further north. But the proportion is variable in wheat of the same vicinity, and it may be increased by the use of animal manures, espe-cially those richest in nitrogen. Liebig noticed that wheat manured with cow dung (which contains but little nitrogen) produced 11.95 per cent. of gluten; while another portion manured with human urine yielded the maximum of gluten, 35.1 per cent. Summer wheat grown in the jardin des plantes at Paris was found to contain 26.7 per cent. of gluten, while a sample of winter wheat gave but 3.33 per cent. As gluten is the most nutritious ingredient in the grains, its proportion has been carefully estimated by chemists. Vauquelin found it in wheat averaging 11.18 per cent.; Dumas 12.50 per cent.; and Dr. Lewis C. Beck, from 33 samples gathered from different parts of the United States, found an average of 11.72, the range being from 9.85 to 15.25 per cent. Prof. Horsford, by ultimate analysis of the wheat, instead of separation of the gluten by mechanical washing, obtained an average of 15.14 per cent. from six samples.
Payen found the proportions of gluten and other nitrogenous matters in wheat to range from 11.20 to 22.75 per cent.; in rye, 13.15; barley, 13.96; oats, 14.39; corn meal, 12.50; rice, 7.05. Prof. Johnston found in English fine wheat flour 10, in bran of the same flour 18, in Scotch oatmeal 18, and in corn meal 12 per cent. of gluten. It is found by very careful and repeated analyses that the bran of wheat and of most other cereals is richer in gluten, and consequently more nutritious, than the rest of the grain. Hence the preference for flour that by thorough bolting has been most completely deprived of bran is unwise; and the whitest flour is less valuable for its nutritive qualities than that made from the whole grain. The bran sometimes constitutes one quarter or more of the grain, and, according to the analyses of Prof. Johnston, contains 14 to 18 per cent. of gluten, while the fine flour contains only 10 per cent. Gluten is readily reduced in quantity, and its tenacity is diminished by injury to the grain.
Flour dealers and bakers judge of the quality of flour by the tenacity of the dough made from a few grains of it. - The subject is further treated under Aliment.