One of the most common questions in sourdough baking is:
“How long should I bulk ferment my dough?”
The honest answer is that there is no single time that works for every loaf.
The speed of fermentation is heavily influenced by the temperature of your dough. A dough at 26°C will ferment much faster than a dough at 20°C, even if all other ingredients remain the same.
Understanding this relationship is one of the biggest steps towards becoming a more confident sourdough baker.
What Is Bulk Fermentation?
Bulk fermentation begins the moment you mix your starter into your dough.
During this stage, the bacteria in the culture begin fermenting the flour, producing gas, flavour and structure. This process continues until the dough is ready to be shaped.
Many bakers rely solely on the clock. The problem is that dough does not know what time it is.
It responds to temperature.
That’s why learning to measure dough temperature can dramatically improve consistency.
Why Dough Temperature Matters
Warmer dough ferments faster.
Cooler dough ferments more slowly.
A difference of just a few degrees can shorten or extend fermentation by several hours.
For example:
- Dough at 20°C may require 12–16 hours.
- Dough at 24°C may require around 7 hours.
- Dough at 26°C may be ready in as little as 5 hours.
Using temperature as a guide helps you avoid:
- Under-fermented dough that feels dense and lacks volume.
- Over-fermented dough that becomes sticky and difficult to shape.
- Inconsistent results between seasons.
Bulk Fermentation Temperature Chart
| Dough Temperature | Estimated Bulk Fermentation Time |
|---|---|
| 18–20°C | 12–16 hours |
| 21°C | 10 hours |
| 22°C | 9 hours |
| 23°C | 8 hours |
| 24°C | 7 hours |
| 25°C | 6 hours |
| 26°C | 5 hours |
Important: These times are guides, not rules. Every starter, flour and kitchen environment is different.
Use the chart alongside visual signs of fermentation.
How to Use This Chart
Step 1: Measure Your Dough Temperature
After mixing your dough, use a probe thermometer to take the temperature from the centre of the dough.
Record the result.
Step 2: Refer to the Chart
Find the closest temperature and note the estimated fermentation time.
Step 3: Allow the Dough to Ferment
Perform your stretch and folds as usual and leave the dough to bulk ferment.
Step 4: Check Again Later
After approximately 75% of the estimated time has passed, take the dough temperature again.
Kitchen temperatures often change throughout the day.
Step 5: Adjust if Necessary
If the dough temperature has increased, fermentation may finish sooner.
If it has cooled, allow additional time.
The goal is not to follow the chart perfectly, but to understand what the dough is doing.
Learn to Read the Dough
The best sourdough bakers combine temperature with observation.
Look for signs such as:
- Increased volume
- A domed surface
- Small bubbles throughout the dough
- A light, airy feel when handled
- Slight movement or wobble in the container
These signs are often more important than the clock.
Common Mistakes
Waiting for the Dough to Double
Many sourdough recipes suggest doubling in size.
For most artisan sourdough loaves, this can lead to over-fermentation, especially at warmer temperatures.
Ignoring Seasonal Changes
A recipe that works perfectly in winter may over-ferment in summer.
Always monitor temperature.
Following Time Alone
Two doughs mixed identically can ferment at completely different speeds if their temperatures differ.
Final Thoughts
Bulk fermentation is one of the most important stages of sourdough baking, and temperature is one of the most reliable tools you can use.
Think of this chart as a guide rather than a rulebook.
Over time, you’ll start to recognise how your dough behaves at different temperatures, and you’ll rely less on recipes and more on experience.
That’s when sourdough baking becomes far more enjoyable and consistent.
Remember: Measure the temperature. Observe the dough. Trust what you see.
Use this in your next bake
Use the clock as a reference, not the finish line. Dough temperature, flour and starter strength can move the schedule significantly. Note what the dough looks and feels like at each stage so the next bake becomes easier to judge.