Poolish

A poolish is a Preferment: flour, water, and a small amount of commercial yeast, fermented before the final mix. In King Arthur Baking's baker's-percentage example, the poolish is equal weights flour and water — 100% Hydration on that piece of flour ¹. Calvel treats poolish among the yeast preferments of technical French bread, not as a sourdough Levain ².

It is not a Biga (a stiff family of preferments) and not Pâte fermentée (old dough that already contains salt). The point of the liquid is fermentation in a wet, yeast-only sponge that later becomes part of a Yeast bread dough.

Why the formula looks wrong until you recast it #

Written as one ingredient, King Arthur's French-bread-with-poolish line is 96% poolish, 48% dough water, 3% salt. Split the poolish: their numbers put equal flour and water in it, plus a trace of yeast. Add those weights back onto flour and water and the dough is 65% water and 2% salt — ordinary lean bread, with part of the flour already fermented ¹. That recast is Baker's percentage overall, and the flour that lived in the sponge is Prefermented flour.

What to notice #

Ripe poolish is bubbly, domed, and just beginning to recede, not a dead soup and not a stiff ball. It is still dough food, not a recipe to copy. If you cannot see flour and water separately in the preferment line, you cannot judge salt or hydration.