Guide
Bulk Fermentation by Temperature and Starter Amount
“Bulk until it looks ready” is how you miss dinner. The yeast in your starter works on a clock, and temperature sets how fast that clock ticks. How much starter you mix in decides how many workers are on the shift.
A 20% starter at 24°C with a peaked levain is the calculator's reference point: about five hours to the window. Drop the room to 18°C and that same dough wants a little over eight. Halve the starter at 24°C and you double the wait. The table below is that pattern — not a vibe, a lookup.
Starter percent here means starter weight over bowl flour, not a share of the total dough. A 100 g starter on 500 g flour is 20% — the same 20% that anchors the table.
The timing behind the table
Bulk time halves for every 8.5°C warmer in the 18–30°C band. The rule underneath is simple: warmer dough goes faster, more starter goes faster, a past-peak starter goes faster. Here's the full version for the curious:
The timing rule
t(T) = 5.0h · 2((24 − T) / 8.5) · (20% / inoc) · maturity
Reference: 5.0 hours at 24°C with 20% peaked starter. The usable window is ±18% around that center — how the dough feels and how strong your starter is still matter, but they no longer get to invent the hour.
The table: read down for more starter, right for warmer dough
Hours to the end of bulk with a peaked starter. Gold cell is the 5.0 h reference. Read down to add starter, read right to warm the dough.
| Dough °C | 10% | 15% | 20% | 25% | 30% |
|---|---|---|---|---|---|
| 18° | 16h 19m | 10h 52m | 8h 9m | 6h 31m | 5h 26m |
| 20° | 13h 51m | 9h 14m | 6h 56m | 5h 33m | 4h 37m |
| 22° | 11h 46m | 7h 51m | 5h 53m | 4h 43m | 3h 55m |
| 24° | 10h | 6h 40m | 5h | 4h | 3h 20m |
| 26° | 8h 30m | 5h 40m | 4h 15m | 3h 24m | 2h 50m |
| 28° | 7h 13m | 4h 49m | 3h 37m | 2h 53m | 2h 24m |
| 30° | 6h 8m | 4h 5m | 3h 4m | 2h 27m | 2h 3m |
Columns are starter as a percent of bowl flour. A 20°C kitchen at 10% starter is a 13h 51m bulk — overnight, not “a little slow.” The same dough at 30% and 26°C is a 2h 50m sprint. Pick the cell that matches the clock you actually have.
How to hit a clock
Want five hours in a 20°C kitchen? Temperature alone stretches the reference by ~1.39×. You need roughly 28% starter, not 20%, to put the center back on five hours. The calculator solves this live when you change dough temp and starter weight.
Warm kitchen, small starter. 10% at 28°C is still about 7 hours — not a crash. Using less starter is a valid schedule, not a defect, as long as you own the hour.
Cold kitchen, big starter. 30% at 18°C lands near 5h 30m. That is how you keep a weekday bake when the house sits at 64°F.
Your starter's ripeness still moves the window
The table assumes a peaked starter. A young or past-peak culture stretches or shrinks the whole table:
Young · 1.22×
Just doubled, still sweet. Bulk runs ~22% longer. Use when the jar is early and you can wait.
Peak · 1.00×
Domed, just starting to fall. This is what the table runs on. Mix here unless you have a reason not to.
Late · 0.88×
Acidic, receded. Bulk runs ~12% faster and tastes sharper. Fine for rye and country loaves.
DDT: the water temp that makes the table true
Ambient air is not dough temperature. Friction from mixing, flour from a cold pantry, and a warm starter all shift the mix. Desired dough temperature (DDT) is the number the table actually runs on. The calculator finds the water temperature that lands your dough on the cell you picked:
Desired dough temperature
Twater = 4 · DDT − Tflour − Troom − Tstarter − friction
In plain English: your water temp makes up for cold flour, a cool room, warm starter, and mixing friction — so the dough lands at your target temp, not the room's.
- Target DDT
- 24°C
- Flour / room / starter
- 21 / 22 / 23°C
- Friction
- 1°C
Table reference row
Calculator defaults
Hand mix, light
Water at 29°C → 4×24 − 21 − 22 − 23 − 1
Mixer friction is higher (often 4–8°C). If the water temperature drops below fridge temp, you need ice or a cooler room — the numbers are telling you the table cell is unreachable from this kitchen. If it climbs past ~40°C you will shock the culture; lower your DDT or mix gentler instead.
Folds ride the same clock
The calculator packs coil folds into the first 40% of bulk, capped at two hours: every 40 minutes at 21°C or below, every 30 in the middle, every 25 at 27°C or above. A 3-hour warm bulk does not get six folds. A 10-hour cool bulk does not get twelve. The table sets the hour; fold spacing follows.
Hydration is a different failure mode. If the dough is a puddle before bulk even starts, read The flour hydration ceiling.