A levain is a portion of starter fed for use in a particular dough. It is not a different species of culture. Keep some starter separately for future maintenance instead of using your entire supply in the loaf.
Read the numbers correctly
20 g starter + 100 g flour + 100 g water produces 220 g levain at a 1:5:5 feeding ratio. If the seed starter is at 100% hydration, the resulting levain is also at 100% hydration. These numbers specify quantities, not a promise that it will peak in four or six hours.
Assess activity, not floating alone
Mark the starting level and watch expansion over successive feeds under comparable conditions. Readiness depends on the formula, temperature and starter history. A floating sample has trapped gas; it does not independently establish strength, maturity or safety. A sample may sink after gas is disturbed.
Plan without wasting the build
Calculate the recipe amount plus the small handling allowance you actually need. Record the feeding time and when the starter reaches its usual high point. Use that record to plan a later bake instead of relying on a universal timetable.
For the definitions behind the arithmetic, see the starter guide.
Sources & scope
Source-based explanation and editorial checklists by SourdoughStart, operated by Tag Ad Limited. AI-assisted article revised 2026-10-12. Source links are not endorsements.
Revision note: prepared for the new reference-led edition. Suggest a correction.