How to use the bulk fermentation calculator
Enter the temperature of your dough right after mixing, how much starter you used, and the share of whole grain flour. The calculator estimates how long bulk fermentation will take and how much the dough should rise before you shape it.
Treat the time as a guide – the dough, not the clock, decides. Starters vary a lot in strength, so check the signs below from about two-thirds of the way through.
Why temperature matters so much
Yeast and lactic acid bacteria are very sensitive to warmth. As a rough rule, fermentation runs twice as fast for every 7 °C (about 13 °F) increase. That's why the same recipe can finish bulk in 4 hours in summer and take 10 hours in a cold winter kitchen.
| Dough temperature | Typical bulk (20% starter) |
|---|---|
| 18 °C / 64 °F | 7½–10½ hours |
| 21 °C / 70 °F | 5½–7½ hours |
| 24 °C / 75 °F | 4½–6 hours |
| 26 °C / 79 °F | 3½–4½ hours |
To make bake day predictable, control the dough temperature from the start with the water temperature calculator.
How to tell bulk fermentation is done
- It has grown by the target amount – often 50–75%. Use a straight-sided container and mark the starting level.
- The surface is domed, smooth and slightly glossy, with a few bubbles.
- You see bubbles on the sides and bottom of the container.
- It jiggles like set jelly when you shake the container, and feels airy and light.
- The edges pull away from the container cleanly and the dough holds its shape when tipped out.
Why the target rise changes with temperature
Warm dough keeps fermenting quickly after shaping, so you end bulk earlier (around 30–50% rise). Cool dough ferments slowly afterwards, so it needs more rise during bulk (75–100%). If your shaped dough goes into the fridge for a long cold proof, you can stop at the lower end of the range.
How we estimate
We start from about 5 hours at 24 °C with 20% starter, adjust for temperature (doubling or halving every 7 °C), for starter amount (less starter means more hours because the yeast population needs more time to grow), and shorten slightly for whole grain flour, which ferments faster.
Frequently asked questions
How long should sourdough bulk ferment?
At 24 °C / 75 °F with 20% starter, around 4½–6 hours. At 21 °C / 70 °F it is closer to 5½–7½ hours, and at 18 °C / 64 °F it can take 8–10 hours or more. Temperature matters far more than the clock.
How do I know when bulk fermentation is done?
The dough has grown by the target amount (often 50–75%), feels airy and jiggly, has a domed surface with some bubbles on top and sides, and pulls away from the container cleanly. Use a straight-sided container so you can measure rise.
Why is my bulk fermentation taking so long?
Usually a cool kitchen, a starter that wasn't at peak, or a low starter percentage. Warm the dough (an oven with just the light on often sits around 26–28 °C / 78–82 °F), or use warmer water next time – our water temperature calculator helps.
Can bulk fermentation go too long?
Yes. Over-fermented dough becomes slack, sticky and very sour, tears when shaped and spreads flat. When in doubt at a warm temperature, end bulk a little early and let the cold retard finish the job.