Enter your dough temperature, starter percentage, and flour type to estimate how long bulk fermentation will take — with a live fold-and-shape timeline and a temperature reference chart.
Every +8°C roughly halves bulk time. Set your real dough temp in the calculator below.
Live calculator · updates as you type
Your dough
75°F
60°75°90°
20%
5%20%30%
Flour type
Estimated bulk time
4h 17m – 5h 48m
Midpoint estimate5h 3m
Fermentation riskNormal range
Fold & shape timeline
0hStart
1h 1m1st fold
2h 1m2nd fold
3h 2mFinal fold
5h 3mShape
Temperature × time reference
Dough temp5% starter10% starter20% starter
18°C / 64°F28–34h14–17h7–9h
20°C / 68°F22–26h11–13h5.5–7h
22°C / 72°F16–20h8–10h4–5h
24°C / 75°F12–15h6–7.5h3–4h
26°C / 79°F9–11h4.5–5.5h2.5–3h
28°C / 82°F6–8h3–4h1.5–2h
30°C / 86°F4–5h2–2.5h1–1.5h
White bread flour at sea level. Wholemeal ferments ~15% faster; rye ~30% faster.
Times are estimates. Actual bulk duration varies with flour strength, starter health, ambient humidity, and dough hydration. Always judge by dough feel: look for 50–75% volume rise, a domed surface, bubbles at the sides, and a jiggle when the bowl is shaken.
How long will bulk fermentation take?
Bulk fermentation time comes down to dough temperature and starter percentage, with flour type nudging it faster or slower. Here are four fully worked cases — set the same numbers in the calculator above to see your own timeline.
24°C / 75°F · 20% starter · white5–7 hours
The everyday same-day window — end at a 50–75% rise.
31°C / 88°F · 20% starter · white2.5–3.5 hours
If your sourdough is at 88°F it moves fast — check from 2 hours.
20°C / 68°F · 10% starter · white10–14 hours
A cool kitchen with low starter — an overnight bulk.
400g of active starter on 1000g flour is 40% — a fast, high-inoculation bulk.
Bulk fermentation guide
Use the numbers — then read the dough.
Temperature, starter percentage, and flour type are the three biggest variables that control bulk fermentation timing. The calculator gives you a time window; this guide explains what's happening inside the dough and how to recognise when it's actually ready.
Coolest range18–21°C
Slow, acid-forward fermentation. Good for overnight bakes and complex flavour.
Everyday range22–26°C
Balanced timing that suits most same-day and next-morning bake schedules.
Warmest range27–30°C
Fast, active fermentation. Watch closely — dough can overproof in under 3 hours.
Key relationship+8°C = ½ the time
For every 8°C (14°F) increase in dough temperature, fermentation speed roughly doubles. Halving starter percentage has a similar effect — it approximately doubles bulk time at the same temperature.
01
How to use this bulk fermentation calculator
Enter your dough temperature using the slider — toggle between Celsius and Fahrenheit to match the thermometer you use. Set your starter percentage: this is the weight of starter as a percentage of total flour in the recipe. Finally, choose your flour type to account for differences in fermentation speed between white, wholemeal, and rye.
The calculator outputs an estimated bulk fermentation window, a midpoint estimate, and a visual timeline from mixing to shaping. A reference table below the calculator shows how temperature and starter percentage interact across a practical range so you can plan bakes ahead even when you change one variable.
02
What is bulk fermentation?
Bulk fermentation is the first and most important fermentation stage in sourdough baking. It begins the moment you mix your dough and ends when you divide or shape it. During this time, yeast produces carbon dioxide that raises the dough, and lactic acid bacteria produce the organic acids that give sourdough its depth of flavour.
The word "bulk" refers to the fact that the entire batch of dough ferments together as one mass, before being divided into individual loaves. Getting bulk fermentation right is the single biggest factor in determining whether a sourdough loaf will have good structure, a healthy oven spring, an open crumb, and a complex taste.
03
Why dough temperature controls bulk fermentation
Temperature is the most powerful variable in bulk fermentation because yeast and bacterial activity roughly double or halve with every 8°C (14°F) change in dough temperature. A dough that takes 8 hours at 20°C will take closer to 4 hours at 28°C. This relationship is not perfectly linear at extreme temperatures, but it holds well in the practical baking range of 18–30°C.
Dough temperature is not the same as room temperature. Friction from mixing warms the dough, and the temperature of your flour, water, and bowl all contribute. Serious bakers use a probe thermometer to measure the actual dough temperature rather than relying on ambient air temperature. The difference can be 2–4°C, which translates directly into bulk fermentation time.
Temperature effect on bulk time (20% starter, white flour)
Starter percentage — the weight of starter as a proportion of total flour — directly controls how much active yeast and bacteria you introduce at mixing. More starter means more microbial activity from the start, so fermentation accelerates. The relationship is roughly inverse: halving starter percentage approximately doubles bulk time at the same temperature.
Most sourdough recipes use between 10% and 25% starter. Lower percentages (5–10%) are common when bakers want a longer, more acidic fermentation, often overnight in the fridge. Higher percentages (20–30%) are used when baking same-day or when working in a cool kitchen where fermentation would otherwise stall.
05
How flour type changes bulk fermentation
White bread flour is the slowest to ferment because the bran and germ have been removed. Wholemeal flour retains more of the wheat kernel, including bran particles that carry native yeast and bacteria as well as enzymes that break down starch more readily. This typically speeds fermentation by around 15% compared to an equivalent white formula.
Rye flour has an even more dramatic effect. It contains pentosan sugars that absorb water aggressively, a high enzyme load, and different starch behaviour. Even small amounts of rye — 10–20% of total flour — can measurably accelerate bulk fermentation. At 100% rye, bulk times can be 30–40% shorter than white flour at the same temperature, and dough requires careful monitoring.
06Readiness check
How to judge when bulk fermentation is done
The calculator gives a time range, but the final call should always be the dough itself. Experienced bakers look at four things: volume increase, surface appearance, container behaviour, and dough feel. Together these give a reliable picture of fermentation progress.
Aim for 50–75% volume increase. A flat-bottomed, straight-sided container with a rubber band at the start height makes this easy to measure. The surface should dome slightly — not be perfectly flat — and you should see small bubbles breaking through the dough. When you shake the container, the dough should wobble loosely. When you pull a small piece, it should stretch without tearing.
Volume rise50–75% above starting volume is a reliable target for most formulas.
SurfaceSlightly domed with fine bubbles visible at the sides and top.
Jiggle testShake the container gently — a jiggly, loose movement means good fermentation.
WindowpanePull a small piece thin enough to see light through without tearing.
SmellYeasty, mildly tangy, slightly sweet — not sharp or alcoholic.
07
Troubleshooting bulk fermentation
Under-fermentation produces dense, tight dough that tears when shaped. The loaf has poor oven spring, a thick crust, and an overly chewy crumb. If your dough hasn't risen after the expected time, check whether your starter is active — it should double within 4–8 hours of feeding at room temperature. Also check your actual dough temperature with a probe thermometer.
Over-fermentation produces slack, sticky dough that spreads rather than holding its shape. The loaf flattens in the oven, the crust browns unevenly, and the crumb can be gummy. Once bulk is obviously over, do not try to recover it with more folding — shape immediately, skip final proof, and bake straight away or put in the fridge. Keep notes so you can adjust timing on the next bake.
08
Bulk fermentation and cold retarding
Many bakers complete bulk at room temperature, then move the shaped dough to the fridge (cold retard) for 8–16 hours before baking. This gives flexibility: you can bake on your own schedule rather than when the dough demands it. The cold slows fermentation dramatically but does not stop it — a shaped loaf in a 4°C fridge is still slowly fermenting.
Some recipes extend bulk fermentation itself into the fridge — a long, cold bulk followed by a shorter final proof at room temperature. This produces a more acidic loaf with a more complex flavour. The calculator models ambient temperature bulk; if you plan to cold-retard during bulk, reduce the estimated time by 60–70% and rely more heavily on dough signs.
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FAQ
Bulk fermentation questions
Common questions about timing, temperature, and technique.
How long should bulk fermentation take?
At 24°C (75°F) with 20% starter and white flour, bulk fermentation typically takes 3–5 hours. At 20°C (68°F) with 10% starter it can take 10–14 hours. Temperature and starter percentage are the two biggest variables.
What temperature is best for bulk fermentation?
Most bakers target 24–26°C (75–79°F) for active, controlled bulk fermentation. Below 18°C activity slows dramatically and above 30°C the dough can overproof quickly. A consistent ambient temperature matters more than the exact number.
My sourdough is 88°F — how long to bulk ferment?
At 88°F (31°C) with a typical 20% starter and white flour, bulk fermentation runs fast — roughly 2.5–3.5 hours to a 50–75% rise. Start checking the dough from about 2 hours, because at this temperature it can tip into overproofing quickly. Lower starter percentages or wholemeal flour shift the window, so use the calculator with your exact numbers and confirm by the rise, not the clock.
How long is bulk fermentation with 400g of active starter?
It depends on the flour weight, since what matters is starter percentage. 400g of active starter on 1000g of flour is 40% inoculation — a fast bulk of roughly 3.5–5 hours at 24°C (75°F) with white flour. On 2000g of flour that same 400g is 20%, closer to 5–7 hours. Enter your starter percentage and dough temperature above for a tailored window.
How do I know when bulk fermentation is done?
Look for a 50–75% increase in dough volume, a domed or slightly convex surface, bubbles along the sides and top of the container, and a light jiggle when you shake the bowl. The dough should feel airy and extensible, not dense or tight.
Does starter percentage really change bulk time that much?
Yes — significantly. At the same temperature, dropping from 20% to 5% starter roughly quadruples the bulk fermentation time. Higher starter percentage means more yeast and bacterial activity from the start, so fermentation accelerates.
Why does flour type affect bulk fermentation timing?
Wholemeal and rye flours contain more wild yeast and bacterial food from bran and germ, so they ferment faster than white flour. Rye in particular can cause the dough to ferment 25–35% faster than a white-only formula at the same temperature.
What happens if I over-ferment during bulk?
Overproofed dough becomes slack, sticky, and nearly impossible to shape. The gluten structure weakens, the dough spreads flat during baking, and the loaf may have a gummy crumb. If you suspect overfermentation, shape immediately and go straight to a cold proof.
