Fermentation Management

A sourdough savant can judge fermentation by aroma, surface tension, and bounce. But for beginners, these clues are often subtle — even invisible.

The easiest and most reliable way to track fermentation is by watching dough expansion. But even that can be misleading. (I've even heard an astrophysicist get volumetric measurements wrong.) Here’s the catch: if a dough ball’s dimension doubles, the volume increases eightfold. Dough doesn’t just rise up — it also spreads out and deepens. That makes growth volumetric, not linear. This "cubing" effect can fool the eye. So instead of guessing, use a graduated container — like a clear measuring pitcher or straight-sided bin with marked volume lines — and watch for the dough to double or triple in volume.

To really manage fermentation, you need to understand the three overlapping biological processes driving it:

1. Lactic acid bacteria (LAB) produce lactic and acetic acids — giving sourdough its tang, improving shelf life, and boosting digestibility.
2. Wild yeasts produce carbon dioxide (CO₂), causing the dough to rise and creating flavor complexity.
3. Enzymes (like amylase and protease) break down starches and proteins into sugars and peptides, which feed the LAB and yeasts and unlock deeper nutrition.

These processes all depend on temperature — and their speed follows a bell curve:

• At 35°F (refrigeration), fermentation slows dramatically and can take 2–4 days.
• Every 10–15°F rise doubles fermentation speed.
• Maximum activity hits around 108–110°F. Beyond that, fermentation stalls — the culture starts to pasteurize (cook), and microbial life dies off.

So here’s the big idea: Fermentation is about controlling time and temperature.

• Raise the temp to speed it up.
• Drop the temp to slow it down.

📈 For example: At 75°F, fermentation runs at a steady, moderate pace. Push it to 105°F and things move 4× faster. Drop to 35°F and it slows 4×. That’s a 16-fold range depending on temperature alone.

My own baking cycle usually lasts 20–36 hours — but I’ve pulled off a successful bake in under 5 hours. I’ve also stretched it to 72 hours. Here’s the key: longer, cooler fermentation produces bread that’s deeper in flavor, easier to digest, richer in nutrients — and downright more satisfying to eat.

📊 Fermentation Speed by Temperature

Temperature (°F) Speed Effect 35°F ❄️ Very Slow Cold retard (2–4 days) 75°F 🐢 Moderate Room temp fermentation 105°F ⚡ Fast Warm proofing 110°F+ ❌ Stops Culture dies, fermentation halts

🧠 Sidebar: Time Isn’t the Only Variable — Temperature Is Too
We often think of fermentation in terms of hours. But time is only half the story. Temperature controls the pace. Want a 5-hour boule or a 72-hour batard? It’s not about rushing or waiting — it’s about changing the environment.