An overnight bulk lets the dough do its slow work while you sleep: mix in the evening, shape in the morning. Whether it works at room temperature depends on how warm the kitchen stays overnight and how much starter goes in. This guide gives the starter amount the calculator's model predicts for an 8-, 10- or 12-hour night, shows where that stops working and says what to check in the morning.
The short answer
In the calculator's model, half the starter makes bulk only about a third longer. So the starter amount can stretch bulk by a few hours, but it cannot turn a warm kitchen into an overnight one. The model predicts that an overnight bulk at room temperature fits a cool kitchen, about 16–18°C (61–64°F), or 20°C (68°F) for a shorter night. In a 22°C (72°F) kitchen it predicts about 8 h of bulk even with 10% starter: enough for an 8-hour night, not for a longer one. At 24°C (75°F) it is about 6½ h. In those kitchens, do the bulk during the day and let the fridge take the night instead (see below).
How much starter for your night
The starter amount here is the weight of ripe levain as a percentage of the flour you add, with the levain at 100% hydration, as in the bake schedule calculator; how much starter in sourdough explains the convention. "Night" means the time from mixing to the morning check. The end of bulk is a rise of about 50–75%, with a domed, jiggly top, as in bulk fermentation by temperature.
The table gives the starter amount the model predicts for the dough to reach the end of bulk after 8, 10 or 12 hours, by the temperature the kitchen holds overnight:
| Kitchen overnight | 8-hour night | 10-hour night | 12-hour night |
|---|---|---|---|
| 16°C (61°F) | over 30% | about 25% (extrapolated) | about 16% |
| 18°C (64°F) | about 27% (extrapolated) | about 16% | about 10% (check early) |
| 20°C (68°F) | about 17% | about 10% (check early) | below 10% (see below) |
| 22°C (72°F) | about 10% | below 10% (see below) | below 10% (see below) |
| 24°C (75°F) | below 10% (see below) | below 10% (see below) | below 10% (see below) |
The model's starter term is fitted to one published series of test doughs with 5–20% starter at 19–23°C (The Sourdough Journey, bulk fermentation timetables). The calculator warns that below 10% the model extrapolates, and above 20% the numbers are the model's extrapolation too, so the table leaves out amounts under 10%. "About 10% (check early)" means the exact figure is just under 10%: use 10% and check the dough an hour or two before the end of the night. "Below 10%" means the kitchen is too warm for that night. The 16°C and 18°C (61°F and 64°F) rows are colder than the test doughs and the 24°C (75°F) row is warmer, so treat them as the model's extrapolation too; in a cold kitchen, check early.
Read it this way: in an 18°C (64°F) kitchen, the model predicts that about 16% starter reaches the end of bulk after about 10 hours. In a 16°C (61°F) kitchen, about 16% gives a 12-hour night.
The dough and the kitchen have to hold their temperature
The model uses one temperature for the whole night: the dough's. Mix with water that brings the dough to about the kitchen temperature, so it starts where it will stay; the DDT formula works out the water temperature. The model also assumes the room holds steady. A kitchen that cools when the heat is turned down at night slows the dough, and one that warms with the morning sun speeds it up. Measure the temperature where the dough will sit, ideally overnight, rather than going by the thermostat setting. If you are unsure, pick the lower starter amount: a dough that is a little behind in the morning is easier to rescue than one that has gone too far.
A worked example
An 18°C (64°F) kitchen, 500 g of flour at 70% water and a 10-hour night, with 15% starter (the nearest round amount), mixing at 20:00 and checking at 06:00:
- Build the levain about 7¾ h before you mix, around 12:15: 16 g starter, 32 g flour and 32 g water (a 1:2:2 feed, 80 g). That is the model's peak time for a 1:2:2 feed at 18°C (64°F) (starter feeding ratio); a warmer daytime kitchen gets it there sooner, so use it when it has risen and domed.
- Mix at 20:00: 500 g flour, 350 g water at a temperature that brings the dough to about 18°C (64°F), 10 g salt and 75 g of the levain at its peak, which is 15% of the flour. Put the dough in a straight-sided container and mark the level. The model predicts about 10 h of bulk to a 50–75% rise at 18°C (64°F) with 15%.
- Do the folds before bed, in the first hours of bulk. Stretch and fold gives the number of sets and the spacing for your dough and kitchen.
- Check at 06:00 (below).
The morning check
Look at the dough before you look at the clock:
- About 50–75% bigger, domed and jiggly, with bubbles at the sides: bulk is done. Pre-shape, rest, shape, then proof at room temperature (how long to proof sourdough after shaping) or retard the shaped loaf in the fridge (cold retard vs. same-day).
- More than about 75% bigger, slack, with large bubbles on top: it went further than planned. Skip the pre-shape and bench rest: shape it once, gently, and put it in the basket. Chill it only while the oven heats, then bake; a long retard would take it further. Next time, use less starter or a cooler spot.
- Less than about 50% bigger, tight, few bubbles: it needs more time. Move it somewhere warmer, around 24–26°C (75–79°F), such as an oven with only the light on (check it with a thermometer), and look at it every 30–60 minutes. Next time, use a little more starter.
When the kitchen is too warm
If the table says "below 10%" for your night, turn the plan around: build the levain in the morning and mix early enough that the calculator's bulk time ends in the evening, let the dough bulk during the day, then shape it and retard the shaped loaf in the fridge at about 4°C (39°F) until the morning bake. The calculator's model does not cover the fridge; cold retard vs. same-day explains how to plan the retard and how to tell the loaf is ready. In a warm kitchen, cooler water also helps hold the dough back, as summer sourdough explains.
Common questions
Can I just use very little starter for a warm night?
Not reliably. Below 10% the model is extrapolating, and less starter buys little time: at 24°C (75°F) the model predicts about 5 h of bulk with 20% and 6½ h with 10%. A cooler spot or the fridge does far more.
Is 10% starter at 20°C enough for a 10-hour night?
Nearly. The model predicts about 9¾ h of bulk at 20°C (68°F) with 10%, which is why the table shows "about 10% (check early)" for that night. 10% is the lowest amount this guide gives times for; check the dough after about 8 hours.
Plan it with your numbers
Put your flour, starter amount and kitchen temperature into the bake schedule calculator. It shows the predicted bulk time for your kitchen, so you can try a few starter amounts before you mix. For a cold kitchen, see winter sourdough.