Poolish
A slack pre-ferment of equal weights of flour and water raised with a small quantity of commercial yeast, mixed hours ahead to develop flavour and extensibility.
Also called pouliche (INTERNATIONAL)
A poolish is made for one bake and used entirely. It is conventionally at 100% hydration — equal weights of flour and water — with a very small proportion of commercial yeast, and is left to ferment for several hours or overnight before being mixed into the final dough.
What it contributes is flavour and dough character rather than leavening. The long, slack fermentation produces organic acids and other by-products that a straight dough does not have time to develop, and the extended hydration lets enzymes work on the flour before mixing, which increases extensibility. The yeast quantity is set against the intended fermentation time and temperature: more yeast for a short poolish, strikingly little for a long cold one.
When to throw it away
A poolish is a short-lived commercial-yeast ferment and raises none of the maintenance questions a sourdough starter does. Standard kitchen practice applies: use clean equipment, keep it covered, and discard it rather than using it if it develops fuzzy or coloured growth.
What is living in it
Microbiology
Commercial baker’s yeast, plus whatever lactic acid bacteria the flour contributes and the fermentation time allows to multiply. A poolish is not a wild culture, but a long one is not microbiologically pure either.
Directional statement. The bacterial contribution to a short poolish is small; over a long overnight ferment it is not negligible, which is part of why long pre-ferments taste different.
RecordedEstablished practice, not a measured result
Hydration
Typical hydration
100% (typically 100%)
100% is definitional for a poolish rather than typical of it. A pre-ferment at a different hydration is generally called something else — see biga.
RecordedTrue by definition rather than by measurement
How it is kept
Built for one bake
Nothing is held back and nothing is refreshed. The yeast quantity is chosen against the intended time and temperature, which is the only real variable.
Definitional rather than a claim about the world.
RecordedTrue by definition rather than by measurement
How to tell it is ready
These are observations, not a schedule. Time to peak depends on temperature, refreshment ratio and flour, and those interact — so the clock tells you roughly when to look, and the list below tells you what you are looking for.
- Sign 1
- Domed and covered in bubbles, with the surface just starting to flatten or dimple at the centre.
- Sign 2
- Smells winey and faintly alcoholic rather than merely yeasty.
- Sign 3
- Pulls into strands rather than pouring cleanly when tipped.
Related
Built and refreshed from
What separates a poolish from a levain: it is raised with commercial yeast for a single bake rather than carried forward as a population.
The science behind it
A pre-ferment is a way of buying fermentation time for part of the flour, so the science it depends on is the same one with a different schedule.
Compared in
The other side. Poolish exists as a record largely because this comparison needed a real entity to point at rather than a paragraph.
An easier starting point than
A poolish gives most of the flavour benefit of a pre-ferment with none of the maintenance, so it is the honest starting point for a baker who wants better bread but not a dependant.