Whole wheat flour and flour made from grains such as rye, barley, buckwheat, rice, oats, millet, corn, and soy all contribute distinctive tastes and textures, as well as nutrition, to breads. They also make them heavier and denser. Typically, some measure of bread flour is included in formulas calling for whole wheat or nonwheat flours in order to develop a light, open crumb.
The bran in whole-grain flours interferes with the development of gluten. Bran cuts the strands of gluten, inhibiting their development and reducing their ability to trap the carbon dioxide produced by the yeast. The higher the percentage of whole wheat or nonwheat flour in a formula, the more pronounced its effect will be on the characteristics of the finished loaf.