Barley and their hybrids and derivatives, barley contains gluten, which makes it an unsuitable grain for consumption by people with gluten-related disorders, such as celiac disease, non-celiac gluten sensitivity and wheat allergy sufferers, among others. Nevertheless, some wheat allergy patients can tolerate barley or rye. Barley is a key ingredient in beer and whisky production. Two-row barley is traditionally used in German and English beers. Six-row barley was traditionally used in US beers, but both varieties are in common usage now. Distilled from green beer, whiskey has been made primarily from barley in Ireland and Scotland, while other countries have used
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