Why starter changes your hydration
A sourdough starter is flour and water. A 100% hydration starter is half flour, half water by weight. If a recipe adds 100 g of starter, it really adds 50 g of flour and 50 g of water, and the true hydration is different from the water ÷ flour you see in the recipe.
The formula
starter flour = starter ÷ (1 + starter hydration)
true hydration = (water + starter water) ÷ (flour + starter flour)
Example: 450 g flour, 315 g water and 100 g of 100% starter. The starter adds 50 g flour and 50 g water, so hydration is 365 ÷ 500 = 73%, not the 70% you'd get from 315 ÷ 450.
What hydration should I use?
- 65–70%: easier to handle; good for sandwich loaves and beginners.
- 70–78%: typical open-crumb country sourdough.
- 80%+: very open crumb, needs strong flour and practiced shaping.
Whole-grain flours absorb more water, so the same percentage feels stiffer with whole wheat than with white flour.
Frequently asked questions
Does sourdough starter count towards hydration?
Yes. The water and flour in the starter are part of the dough. Counting them gives the true hydration, which is what determines how the dough behaves.
What is 100% hydration starter?
A starter fed with equal weights of flour and water, e.g. 50 g flour and 50 g water.
How do I lower hydration if my dough is too wet?
Hold back some water at the start and add it only if the dough can take it. The calculator shows how much water to add for a target hydration.