Gluten is conjoined with starch in the endosperm of various grassrelated grains. Wheat prolamins are called gliadins, barley prolamins are hordeins, rye prolamins are secalins and oats prolamins are avenins, which are collectively named gluten. Oat avenin toxicity in people with gluten-related disorders depends on the oat cultivar consumed because the immunoreactivities of toxic prolamins are different among oat varieties. Also, many oat products are cross-contaminated with other gluten-containing cereals.
The fruit of most flowering plants have endosperms with stored protein to nourish embryonic plants during germination. True gluten is limited to the grains listed above. The stored proteins of maize and rice are sometimes called glutens, but their proteins differ from true gluten.
Gluten is a protein complex that accounts for 75 to 85% of the total protein in bread wheat. Gluten is prepared from flour by kneading the flour under water, agglomerating the gluten into an elastic network, a dough, and then washing out the starch. Starch granules disperse in cold/low-temperature water, and the dispersed starch is sedimented and dried. If a saline solution is used instead of water, a purer protein is obtained, with certain harmless impurities departing to the solution with the starch. Where starch is the prime product, cold water is the favored solvent because the impurities depart from the gluten.
In home or restaurant cooking, a ball of wheat flour dough is kneaded under water until the starch disperses out. In industrial production, a slurry of wheat flour is kneaded vigorously by machinery until the gluten agglomerates into a mass. This mass is collected by centrifugation, then transported through several stages integrated in a continuous process. About 65% of the water in the wet gluten is removed by means of a screw press; the remainder is sprayed through an atomizer nozzle into a drying 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 transported to a receiving vessel. In the final step, the processed gluten is sifted and milled to produce a uniform product