Oat vary among oat varieties. Also, oats products are frequently cross-contaminated with other gluten-containing cereals during grain harvesting, transport, storage or processing. Pure oats contain less than 20 parts per million of gluten from wheat, barley, rye, or any of their hybrids. Use of pure oats in a gluten-free diet offers improved nutritional value from the rich content of oat protein, vitamins, minerals, fiber, and lipids, but remains controversial because a small proportion of people with celiac disease react to pure oats. Some cultivars of pure oat could be a safe part of a gluten-free diet, requiring knowledge of the oat
Rye bread upon this mixing of grains. Use of high-gluten wheat flour also makes possible multigrain breads, such as the "rye and Indian" bread of the American colonies, which combined rye and wheat with cornmeal in one loaf. Rye bread contains phenolic acids and ferulic acid dehydrodimers. Pure rye bread contains only rye flour, without any wheat. German-style pumpernickel, a dark, dense, and close-textured loaf, is made from crushed or ground whole rye grains, usually without wheat flour, baked for long periods at low temperature in a covered tin. Rye and wheat flours are often used to produce a rye bread with