Collage of before and after mixing flour, water, and starter to create a levain for sourdough bread
Before and after: A levain grows to more than triple its original volume.
The levain is whatever portion of mature starter you use to mix into your dough. This distinction between a starter and a levain is slight, but bakers refer to “building” a levain prior to mixing, a concept which underscores both the scaling necessary to turn a relatively small stash of starter into a large enough quantity to leaven one or more loaves of bread, as well as the scheduling required to pull it all off, so that the bread is ready to be baked at the desired time. For instance, you may keep a relatively small total starter amount (50 grams or less) on a day-to-day basis. But 50 grams of starter won’t take you very far—doubly so if you intend on baking multiple loaves. To produce enough starter for baking, we take some portion of the original culture (say, 30 grams) and feed it at least 1:1:1 (starter to flour to water), which gives 90 grams of mature starter to work with. At this feeding ratio, it takes about four to five hours for the levain to reach peak activity at 78-80°F.*
