Rye flour is flour milled from whole rye berries and grains of rye grass. Closely related to wheat flour, it has a slightly sour taste and is used to prepare rye bread and sourdough bread. Loaves of bread produced with rye flour are generally darker and denser than other types of bread. Rye and sourdough breads have a distinctive flavor that are enjoyed by many. Sauerkraut and corned beef are especially good on sourdough bread, and rye bread is a good substitute for white bread for just about any sandwich.

Rye flour can be found in light, medium, or dark colored varieties. The color of the flour depends on how much of the bran has been removed through the milling process. If most of the bran is left in, the flour will be darker. Conversely, if most of the bran has been removed, the flour will be finer and lighter. More nutrients are retained in the flour because the germ and the bran are not separated during the milling process, making it healthier than processed white flour.

The medium color is most commonly found in supermarkets, while light or dark colored rye flour can be found in health food stores or some larger supermarkets with specialty food sections. Pumpernickel flour is one type of dark rye flour, and is used to make pumpernickel bread. The medium flour has much of the bran still in it, giving it a slightly grainy texture that is good for baking bread. If a more powdery flour, similar in texture to traditional white flour, is preferred, light rye flour may be a better option.

There are some issues that should be kept in mind if a baker is attempting to bake with rye flour. It is high in bran and soluble fiber content, but low in gluten. Gluten is part of what helps bread rise, so the lower level of gluten in rye flour can prevent the bread from rising well. This can be remedied by substituting some of the rye flour in the recipe with wheat flour, which will better allow the yeast to develop.

Recipes that call for rye flour may include other suggestions to help the bread rise. A general rule of thumb suggests substituting 1/3 of the amount of rye flour with wheat flour to ensure the bread will rise properly. This means if a recipe called for 1 cup (about 102 grams) of rye flour, for example, you would instead include 2/3 cup (about 68 grams) of rye flour and 1/3 cup (about 34 grams) of wheat or white flour.