A sourdough fermentation timer estimates how long bulk fermentation will take based on your room temperature and starter inoculation percentage. Unlike generic guides, this tool uses the Q10 temperature coefficient formula — the same biological principle that governs yeast activity — plus inoculation percentage to give accurate, personalized timing.
Fermentation Inputs
% of starter relative to total flour weight
Fermentation Estimate
Check-in Points
Note: Actual time varies by starter health, flour freshness, and hydration. Use as a starting estimate — watch the dough, not the clock.
How to Use the Sourdough Fermentation Timer
Bulk fermentation is the most variable and misunderstood step in sourdough baking. Most recipes say "4-8 hours" — a range so wide it is nearly useless. This timer narrows it down using two key variables: your actual room temperature and your starter inoculation percentage.
Step 1: Set Your Temperature Unit
Toggle between °F and °C at the top of the inputs panel. The calculator base is 76°F (24°C) — the ideal bulk fermentation temperature used in most professional recipes. Enter your kitchen's actual ambient temperature.
Step 2: Set Your Inoculation Percentage
Inoculation percentage is the amount of starter as a percentage of total flour weight. If your recipe uses 500g flour and 100g starter, that is 20% inoculation. The slider ranges from 1% (very slow, overnight bulk) to 30% (fast 2-hour bulk). Most home bakers use 15-20%. Lower inoculation develops more complex flavor; higher speeds up the timeline.
Step 3: Select Flour Type
Whole grain flours ferment faster due to extra enzymes and minerals in the bran. Whole rye is the fastest — a 100% rye dough at 20% inoculation at 76°F ferments in about 3.5 hours instead of 4. Whole wheat runs about 10% faster. All-purpose and bread flour have similar timing.
Step 4: Choose Target Rise
The standard endpoint for an open-crumb sourdough is a doubled dough (100% volume increase). For a cold overnight retard, you want only 50% rise before refrigerating — the dough finishes slowly in the fridge. "Just passing poke test" adds 15% buffer time for bakers who prefer the tactile check.
Step 5: Start the Timer
Click "Start Bulk Ferment Timer" when you add your starter to the dough. The countdown shows time remaining and a progress bar. The three check-in points tell you when to observe the dough — look for bubbles on the sides, a dome shape on top, and increased volume at each checkpoint.
Understanding the Q10 Formula
The calculation uses the Q10 temperature coefficient: for every 10°C rise in temperature, fermentation is 2.5× faster. At 66°F (19°C), a 4-hour bulk becomes 10 hours. At 86°F (30°C), it shrinks to under 2 hours. This is why a warm kitchen in summer requires close monitoring, while a cool kitchen in winter allows all-day, flavor-building fermentation.
Frequently Asked Questions
Is this sourdough fermentation timer free?
Yes, completely free with no signup required. All calculations run in your browser using the Q10 temperature coefficient formula. No data is sent to any server.
Is my data private?
Yes, everything runs locally in your browser. No data is stored or sent anywhere. You can use the tool offline once the page has loaded.
What is the Q10 temperature coefficient?
Q10 is a measure of how much faster a biological process (like yeast fermentation) speeds up for every 10°C rise in temperature. Sourdough yeast has a Q10 of approximately 2.5, meaning fermentation is 2.5× faster for every 10°C increase.
What does inoculation percentage mean in sourdough?
Inoculation percentage (often called starter percentage) is the amount of sourdough starter relative to total flour weight. 20% inoculation means 20g of starter per 100g flour. Higher percentages speed up fermentation significantly.
Why does my sourdough take longer or shorter than the estimate?
The estimate is based on a healthy, active starter at peak activity. Variables like starter age since last feeding, flour freshness, dough hydration, and ambient humidity all affect actual timing. Use the estimate as a starting point and rely on dough feel and the poke test.
How does whole wheat flour affect fermentation time?
Whole wheat flour ferments about 10-15% faster than all-purpose or bread flour. The extra enzymes and minerals from the bran accelerate yeast and bacterial activity. The calculator applies a 10% speed-up for whole wheat blends.
What is a good room temperature for sourdough bulk fermentation?
The sweet spot is 24-26°C (75-78°F). Below 20°C (68°F) fermentation slows dramatically. Above 28°C (82°F) it speeds up but can become unpredictable and over-proof. For cooler kitchens, try a longer overnight bulk in the refrigerator.