What Is Levain, and How Is It Different from a Sourdough Starter?

The difference between a main starter and levain is their role, not their ingredients; both are made with flour, water, and starter culture. The main starter is a culture reserve that needs to be maintained. It is never used up completely, because rebuilding it takes days. Levain, by contrast, is temporary: take a spoonful of the main starter, feed it with flour and water, let it mature for a few hours, and add all of it to the dough. Build a fresh levain the next day for another dough.

There are three reasons to build it separately. First is security: because the entire main starter does not go into the dough, the culture remains available even if the dough fails. Second is quantity; if a recipe calls for a lot of starter, build a levain suited to it instead of enlarging the main starter. Third is adapting to the recipe: levain can be fed with the flour that bread calls for and built at different ratios, producing a preferment tailored to the recipe without changing the character of the main starter. A fourth reason is to spread the risk: if the levain takes longer than expected to mature, only that dough is delayed and the culture remains unaffected.

The build is simple. Calculate the amount of levain the recipe needs and take a small piece of the main starter; add flour and water. A common build uses one measure of starter with five measures of flour and five measures of water. The higher the ratio, the longer maturation takes and the milder the flavor remains. Cover the mixture and let it rest until it reaches its peak, indicated by the volume reaching 2 times its initial size.

The main benefit of levain is timing. Choose when to mix the dough, then work backward to build the levain so it will be ripe at that time. It takes longer in a cool kitchen and less time in a warm one; the feeding ratio is also part of the calculation. A levain built at a high ratio can ferment overnight and be ready in the morning. This flexibility is one of the most practical ways to fit sourdough baking into a daily routine. Writing the time on the container also helps, since the levain reaches its peak within a few hours and it is easy to miss.

Add all the ripe levain to the dough; do not set aside and store a portion, since that is the role of the main starter. Before using it, check it with a float test or by its volume and smell. If any levain is left unused, do not waste it; use it in recipes that do not need to rise, such as pancakes, griddle cakes, or crackers. Continue feeding the main starter on its own schedule, and never use it up completely for a recipe. The same idea applies to other preferments such as poolish and biga; each is a portion of the dough that is started in advance.