A type of flour, produced from hard wheat that has been treated to remove the starch. It contains a greater percentage of gluten (at least 70% pure) than other types of flour and a lower percentage of starch. The gluten content of the flour has nearly twice the strength of regular wheat flour. Gluten is the protein that gives bread its elastic quality and aids in the rising process of the dough. Gluten flour is most often used as an additive for various flours that are low in gluten or are gluten free, but it tends to toughen bread if used in excess. It is very useful for the preparation of pizza dough, bagels, and flat breads and rolls. It is often confused with bread flour, which is fortified with additional gluten, but has a lower gluten content than gluten flour.