Desem (Dutch for "leaven") is a type of sourdoughstarter made from whole wheat, spelt or other flours (amaranth or kamut) and water, inoculated by wild yeasts and bacteria, traditionally used in Belgium to make healthy, nutrient-rich bread. The starter is grown in a bed of flour at cool temperatures until it reaches sufficient maturity. The term "desem" also describes the loaf made with this starter. Desem bread made from a mature desem is characterized by a strong rise, and a light texture, and nutty, slightly sour taste. The loaf is similar in process to the French "pain au levain", but made with whole wheat flour and starter instead of white flour.
Desem bread has a strong following in the natural foods community, where it was largely popularized by vegetarian cookbook author Laurel Robertson.