Build levain without double-counting the starter’s flour and water
Plan a target levain mass and hydration by subtracting the flour and water already in your starter, with a reproducible 200 g example.
Method
Baker’s hydration compares water mass with flour mass, not with the mass of the entire mixture. A 100% hydration starter contains equal masses of flour and water. If a recipe calls for a target levain mass, the starter you add already contributes both ingredients. Adding the full target flour and water again makes a larger build than intended.
Write hydration as a decimal h. For a target mass M containing only flour and water, target flour is M ÷ (1 + h), and target water is M minus that flour. Split the starter using its own hydration in exactly the same way. Then subtract starter flour from target flour and starter water from target water. Different starter and target hydrations must not be treated as interchangeable.
For an arithmetic example, plan 200 g of levain at 100% hydration using 20 g of starter also at 100%. The target contains 100 g flour and 100 g water. The starter already provides 10 g flour and 10 g water. Add 90 g flour and 90 g water to the 20 g starter. The resulting total is 200 g, with 100 g of each ingredient.
View data
- Existing starter
- 20 g 10 g + 10 g
- New flour
- 90 g 100 g − 10 g
- New water
- 90 g 100 g − 10 g
Worked example
For an arithmetic example, plan 200 g of levain at 100% hydration using 20 g of starter also at 100%. The target contains 100 g flour and 100 g water. The starter already provides 10 g flour and 10 g water. Add 90 g flour and 90 g water to the 20 g starter. The resulting total is 200 g, with 100 g of each ingredient.
Check the mass balance in two ways: 20 + 90 + 90 = 200 g, and 100 ÷ 100 × 100 = 100% hydration. If either calculated addition is negative, the selected starter amount or hydration is incompatible with the target. Reduce the starter amount or revise the target; a negative ingredient quantity is not an instruction to remove flour or water from a mixed starter.
20 + 90 + 90 = 200 g
100 / 100 × 100 = 100%
This is a two-component mass-balance calculation. It excludes evaporation, retained jar residue, other ingredients and measurement uncertainty. It does not predict fermentation time, readiness, acidity or food safety. Weigh ingredients in one unit and follow an appropriate baking and food-handling process. The supplied numbers are a worked example, not a recommended feeding schedule.
View data
- Target flour
- 200 / 2 = 100 g
- Starter flour
- 20 / 2 = 10 g
- Flour to add
- 100 − 10 = 90 g
Checks and limits
This is a two-component mass-balance calculation. It excludes evaporation, retained jar residue, other ingredients and measurement uncertainty. It does not predict fermentation time, readiness, acidity or food safety. Weigh ingredients in one unit and follow an appropriate baking and food-handling process. The supplied numbers are a worked example, not a recommended feeding schedule.