One of the main ingredients of bread, flour is a powder ground from grains - most typically wheat but some others such as rye or rice can also be used. It can be classified into two main categories, which are whole wheat and white flour. The difference between these being which part of the grain is used to produce it. Whole-wheat flour, as the name suggests, is made with the entire grain. On the other hand, white flour is usually made with just the endosperm (the innermost part of the grain, which has the highest protein content).

Another important property of flour is its protein content. The amount of gluten development a dough has directly correlates to how much protein was in the flour used in it. Considering this, flours designed specifically for bread are usually the ones with the most proteins, with concentrations ranging from 12% to 14%.