Bulk fermentation ends when the dough says so, not when the timer does

This works through judging the end of bulk fermentation in the order the parts actually depend on each other.

What bulk fermentation is doing

During bulk the yeast produce carbon dioxide that inflates existing gas cells, while the gluten network stretches to contain them. At the same time bacteria and flour enzymes are producing acids and sugars that will become flavour and crust colour later.

The structure is being built and inflated simultaneously, which is why the end point is a balance rather than a milestone. Stop too early and there is not enough gas or extensibility; go too far and the network cannot hold what it has made. Every visual cue you use is really an attempt to read that balance from the outside.

The rise you are actually looking for

For most white sourdough at 24 to 25C, ending bulk at a rise of 50 to 75 per cent gives a dough that still has strength to spare. The old instruction to wait for doubling comes from commercial yeast doughs, which ferment faster and acidify far less. Sourdough left to double often has softened so much that shaping tears rather than tightens the surface.

Wholemeal and rye ferment faster still, so 40 to 50 per cent is often the right stopping point for them. The percentage is not sacred, but it is a far better anchor than a stated number of hours.

The aliquot jar

Pinch off perhaps thirty grams of dough after the final fold, press it into a straight-sided jar, and mark the starting level. The small sample sits in the same conditions and rises at the same rate, but you can read it against a ruler.

Mark 50 and 75 per cent on the outside with tape and the judgement becomes a glance rather than a debate. Straight sides matter, because a tapered jam jar will exaggerate the rise near the top. Press the sample in without trapping air, or the starting level is wrong and everything after it is wrong too.

Reading the dough itself

A finished bulk dough jiggles as a single mass when you shake the tub, rather than sloshing or staying rigid. The surface should be domed and slightly convex where it meets the sides, with visible bubbles around the edges. Poking it lightly should leave a dent that fills back slowly and incompletely, not one that springs straight out.

At oven temperature, if the dough smells sharply alcoholic and the surface has gone flat and blistered, it has already gone past the point.

None of these signs is reliable alone, which is why the jar and the feel are best used together.

Temperature changes everything

At 27C a white sourdough might finish bulk in three hours; at 21C the same dough could need six or seven. This is why identical recipes produce wildly different results in a summer kitchen and a winter one. Recording the dough temperature alongside the time gives you a personal chart within about five bakes.

At oven temperature, if the kitchen is cold, a longer bulk is not a problem in itself, provided the dough is still gaining structure. The failure mode of cold fermentation is impatience rather than the temperature itself.

Proving times are written for a warm kitchen, and yours may not be one.

Folds are part of the judgement

Three or four sets of coil folds at forty five minute intervals build strength while telling you how the dough is progressing. Each set should feel stronger and more resistant than the last until the final one, when the dough starts to feel airy and delicate. When a fold no longer holds its shape for a minute afterwards, the dough is near or past its useful limit.

Stop folding for the last quarter of bulk so the gas structure is not knocked out just before shaping. The folds are diagnostic as much as they are structural, which is the part most instructions leave out.

The takeaway

Watch the dough, keep a jar beside it, and let the clock be a rough estimate.

Bake it badly once on purpose. The failure teaches more than the photograph.