Guide
Temperature and Fermentation Time
Every sourdough recipe you read assumes a specific kitchen temperature, usually 76°F. Your kitchen is probably not 76°F. The fermentation multipliers below let you translate any recipe to your actual conditions, and the DDT calculation lets you hit a target dough temp deliberately.
Why temperature controls everything
Sourdough fermentation is enzymatic — yeast and lactic-acid bacteria metabolize flour sugars at rates determined by temperature. Recipes are written assuming a baseline (typically 76°F / 24.4°C). Your kitchen sets the actual temperature, and therefore the actual timing. A cold kitchen slows everything; a hot kitchen speeds everything. Miss this, and you over- or under-proof.
The multiplier table
From Modernist Bread vol 3, with baseline at 76°F. 58°F = 2.5× longer. 68°F = 1.6× longer. 76°F = 1.0× (baseline). 80°F = 0.75× (25% faster). 85°F = 0.55× (45% faster). 90°F = 0.42× (58% faster). Refrigerator retard (38°F) = 10-12× longer. Multiply your recipe's bulk and proof times by the appropriate multiplier to get your actual timing. Our calculator does this continuously.
Case 1: Cold kitchen in winter
Kitchen at 64°F. Recipe says 4h bulk at 76°F. Multiplier at 64°F is ~1.8×. Actual bulk: 7.2 hours. Consider either warming the dough (oven-with-light-on trick, proofing box) or extending bulk and letting flavor develop. Cold kitchens are forgiving for flavor — fermentation happens slowly, acid balance stays clean.
Case 2: Hot kitchen in summer
Kitchen at 82°F. Recipe says 4h bulk at 76°F. Multiplier at 82°F is 0.68×. Actual bulk: 2.7 hours. Hot kitchens are unforgiving — fermentation outpaces gluten development, dough becomes slack and over-acid quickly. Either reduce levain percentage to 10-12%, move dough to cooler location, or get it into cold retard within 2 hours of bulk start.
Case 3: Using cold retard strategically
Hybrid schedule: start bulk at room temp (2h), refrigerate overnight (12h at 38°F ≈ 1h equivalent at 76°F), return to room temp (1-2h). Total elapsed: 16+ hours. Total fermentation equivalent: 4h. You get Monday-night mix → Wednesday-morning bake flexibility without over-fermenting. Used in every professional bakery for schedule control.
Case 4: Dough desired temperature (DDT) calculation
Instead of reacting to kitchen temp, target a specific dough temp. Formula: water temp = (DDT × 3) - (flour temp + room temp + friction factor). DDT target is usually 76°F. If your room is 68°F and flour is 68°F (both at room), friction factor for hand-mixing is ~5°F, so water = (76×3) - (68+68+5) = 228 - 141 = 87°F. Use 87°F water to land at 76°F dough. This is how professional bakers hit consistent dough temp year-round.
FAQ
How do I measure dough temperature?
Instant-read thermometer. Insert to the center of the dough mass; read within 5 seconds. Target 76°F for artisan hearth doughs; 78-80°F for enriched doughs which need warmer fermentation. Re-check every hour of bulk until you have an intuitive sense of what the dough feels like at your target.
Can I proof sourdough in an oven with the light on?
Yes. An oven with just the light on runs 80-90°F — hot for bulk (over-proofs fast) but usable for final proof if you're pressed for time. Better: turn the light on for 30 minutes to warm the interior, turn it off, put dough in the residual-warm oven. Stays around 78°F, which is near-ideal for fast active fermentation.
What's the coldest temperature that still ferments sourdough?
Around 40°F. Below that, yeast and bacteria go dormant — true refrigerator retard. Between 45-55°F, very slow fermentation happens (used for some cold-retard bulk schedules). Above 55°F up to 90°F is active fermentation range. 76°F is the sweet spot for controlled flavor development.