How the Bulk Fermentation Estimate Works
Bulk fermentation is the period when the dough rises in mass before shaping. Its duration depends on three variables: starter percentage (how much active yeast and bacteria you add), dough temperature (which controls fermentation rate), and flour type (whole grain ferments faster).
This calculator uses a kinetics model adapted from documented baking data. The base case — 20% levain at 76°F (24°C) — produces a 4–6 hour bulk ferment, consistent with observations from The Perfect Loaf and King Arthur Baking.
The temperature adjustment uses a Q10 factor (reaction rate doubles per 10°C / 18°F), a well-established biochemical model. A 10°F drop in dough temperature approximately doubles fermentation time; a 10°F increase roughly halves it.
Temperature vs. Fermentation Time (20% starter)
| Dough Temp (°F) | Dough Temp (°C) | Approx. Bulk Time |
|---|---|---|
| 65°F | 18°C | 8–12 hours |
| 70°F | 21°C | 6–8 hours |
| 75°F | 24°C | 4.5–6 hours |
| 78°F | 26°C | 3.5–5 hours |
| 80°F | 27°C | 3–4 hours |
| 85°F | 29°C | 2–3 hours |
Source: approximated from documented observations in Maurizio Leo, The Perfect Loaf (W.W. Norton, 2022), and compiled fermentation time tables from King Arthur Baking.
How to Know When Bulk Is Done
Time is a guide, not a rule. Judge bulk fermentation by these signs:
- Volume increase: 50–75% rise for most recipes (mark your container at the start)
- Surface texture: Slightly domed, airy, with visible bubbles at the edges
- Jiggle test: Shake the container — a properly fermented dough jiggles like Jell-O
- Finger poke test: A poke springs back slowly (not instantly = overproofed; not at all = underproofed)
Cold Retard: Flavor Development and Scheduling
Cold retarding (final proof in the refrigerator at 38–40°F) serves two purposes: it slows fermentation so you can bake at a convenient time, and it develops more complex flavor. The acetic acid bacteria that produce sourness prefer cooler temperatures than the yeasts, so a longer cold retard generally produces a more sour loaf.
For more detail, see our articles on sourdough schedule examples, bulk fermentation temperature guide, and starter feeding ratios. Use the baker's percentage calculator to build your formula.