Sourdough advice is full of clocks — "bulk for 4 hours," "proof overnight" — and clocks are the wrong unit. Fermentation runs on temperature, and the baker who controls dough temperature stops following clocks entirely. Here is the control, and the method that wields it.
The sensitivity
Yeast activity roughly doubles per 5°C (within its comfortable band). A dough at 27°C finishes bulk twice as fast as the same dough at 22°C — which is why the same recipe "worked in winter and failed in summer." The recipe's hours were never the specification; the temperature was.
The control: water temperature
Flour, room, and starter arrive at whatever temperature the house gives them. Water is the one ingredient with a settable temperature — and it is also most of the dough's mass. The desired-dough-temperature (DDT) method:
Water temp = (3 × target dough temp) − flour temp − room temp
The calculator runs it, flags the ice-water cases, and adjusts for the fridge. Measure the mixed dough with a probe thermometer and the feedback loop closes: too warm today, colder water tomorrow.
Seasonal playbooks
| Season | Water | Bulk | Watch for |
|---|---|---|---|
| Summer (28–32°C room) | Ice water | 2–3 hrs, watch not clock | Over-proof collapse; consider a cold bulk |
| Shoulder (20–24°C) | Tap water | 4–5 hrs | Nothing — the default works |
| Winter (16–19°C) | Warm (30–35°C) | 6–9 hrs or overnight cold | Sleepy starter — warm its water too |
Why 76°F / 24.4°C is the default target
It is the temperature where yeast speed and bacterial flavor development stay balanced — doughs rise on schedule and taste complex without going sour. Cooler targets (73°F) stretch time and favor sweeter, milder bakes; warmer (79°F+) trade flavor for speed. Set the target to the schedule you actually have.
One $15 probe thermometer, one week of measuring, and the kitchen's seasons stop being surprises. Temperature is the variable — the DDT method is the steering wheel.