Split a preferment without counting it twice
A ready flour-and-water preferment is part of the dough, not extra dough.
Hydration is a ratio to flour
For a flour-and-water preferment weighing P grams at h percent hydration, flour is P ÷ (1 + h/100), and water is the remaining mass. At 100% hydration the two masses are equal. At 60% hydration they are not.
Try the arithmetic yourself
A 160 g preferment at 60% hydration contains 160 ÷ 1.6 = 100 g flour and 60 g water. A 160 g preferment at 100% hydration contains 80 g of each. The same preferment weight can therefore change both total flour and the overall water-to-flour ratio.
Suppose the final bowl also receives 400 g flour, 240 g water and 10 g salt. With the 60%-hydration preferment, total flour is 500 g and known water is 300 g. Known-water hydration is 60%. Prefermented flour is 100 ÷ 500 = 20% of total flour; preferment mass is 160 ÷ 500 = 32%. These are different quantities.
What to enter
Use the ready preferment's full mass and actual hydration, including any seed culture already inside it. CrumbScale does not calculate feeding schedules, seed additions, ripeness or fermentation timing. A mixture containing salt, oil or other ingredients cannot be represented accurately by this flour-and-water-only role; model its measured additions separately or keep it as Other with the hydration limitation visible.
When scaling, the app scales the whole ready preferment mass once. Its internal flour and water are an accounting breakdown, not another pair of additions to put in the bowl.
Reference reading
For the general convention, see King Arthur Baking: Baker’s Percentage and its discussion of bread hydration. Worked examples and application explanations here are our own. No affiliation or endorsement is implied.