Bulk fermentation is where the loaf is decided, and it is governed by temperature far more than by the clock. Every recipe that specifies four hours of bulk is quietly assuming a room temperature the reader does not have. David Anthes, a home baker in Bend, Oregon, stopped following bulk times in recipes once he started measuring dough temperature, and his consistency improved immediately.
The relevant number is final dough temperature, taken right after mixing. It is a function of flour temperature, water temperature, room temperature, and friction from mixing. Bakers calculate it with a desired dough temperature formula, multiplying the target by three, then subtracting flour temperature, room temperature, and a friction factor to find the water temperature to use. Anthes targets 25 to 26C for most bakes because it produces a bulk that fits a morning without pushing the culture into heavy acid production.
Rate changes steeply across small temperature differences. A dough at 24C might need five hours of bulk. The same dough at 28C might need two and a half. A kitchen that sits at 19C in winter can push bulk past eight hours, and most home bakers who complain about dense loaves in winter are simply cutting bulk short based on a summer schedule. Anthes uses his oven with the light on as a mild proofing box when the house runs cold, and checks it with a thermometer rather than trusting it.
Temperature also shifts what the fermentation produces. Warmer dough favors lactic acid bacteria that generate mild, yogurt like acidity. Cooler and longer fermentation shifts the balance toward acetic acid, which reads as sharp and vinegary. The same starter and the same flour will produce noticeably different flavor at 22C versus 28C. Anthes tracks this because his preference changes with what he is baking. A seeded country loaf can carry more acidity than a plain white loaf.
Reading the dough is more reliable than any target. Volume increase is the standard cue, and 50 to 75 percent is a common endpoint for a moderately strong flour, though the right number depends on flour strength and how much rise gets held back for the oven. An aliquot jar, a small sample of the same dough in a straight sided container, makes volume readable without guessing at a bowl with sloped sides. Anthes keeps one on the counter and marks it at the start.
Physical cues confirm the volume reading. Dough at the end of bulk feels aerated rather than dense, domes slightly at the edges where it meets the container, and shows bubbles at the surface and along the sides. It jiggles as a unit when the bowl is moved. Underfermented dough feels tight and heavy and tears when stretched. Overfermented dough spreads, feels slack and sticky in a way that does not improve with handling, and smells strongly acidic.
Stretch and folds during bulk do two things at once. They build strength by aligning gluten, and they redistribute temperature and food supply through the dough. Three or four sets spaced 30 to 45 minutes apart across the first half of bulk is a common approach. Folds late in bulk degas the loaf without adding much strength.
The method that works is simple to state and hard to skip. Measure final dough temperature, watch percentage rise rather than minutes, confirm with feel, and write down all three. Anthes has a notebook column for each. Over enough bakes the pattern becomes obvious.