Your starter doubles in 4 hours in July. In January it barely budges overnight. Same flour, same feeding ratio, same jar, but a 16°C (61°F) kitchen ferments at less than half the speed of a 24°C (75°F) kitchen. Cold-kitchen sourdough isn't broken sourdough. It's just slower, and the fix is mostly about understanding how temperature drives fermentation, then nudging the dough toward the conditions it actually wants.
This guide covers what changes below 20°C (68°F), how to find or create warm spots, how to adjust timing and starter quantity, and what to do when your bulk ferment stalls.
Why cold kitchens wreck your timing
Yeast and lactic acid bacteria are temperature-sensitive in a non-linear way. The rule that governs everything else here: fermentation slows by about 2.2× for every 8°C (about 14°F) you drop (a touch more than halving), so the gap between a 24°C kitchen and a 16°C one isn't small. It's a factor of more than two.
- 26°C (79°F): fast, often too fast for flavor development
- 24°C (75°F): the "textbook" sourdough temperature most recipes assume
- 21°C (70°F): comfortable, predictable, slightly slower
- 18°C (64°F): the model puts bulk at about 9 hours instead of 5
- 15°C (59°F): fermentation crawls; expect 12+ hours or a stalled dough
The other shift is microbial. Cold favors lactic acid bacteria over yeast, so cold-fermented doughs tend to taste tangier with less rise. This is why fridge retards work for flavor but you can't bulk-ferment a dough at 6°C (43°F) and expect it to puff up.
The single most important number in winter baking is the dough temperature, not the room temperature or the water temperature. If you're not measuring it with a probe thermometer right after mixing, start there. Target a 24–26°C (75–79°F) final dough temperature in winter, and you've already solved half the problem.
Hitting the right dough temperature
In a cold kitchen, water is the only input warm enough to drag the dough up to target, so you run it hot. The arithmetic (how much to subtract for cold flour, a cold room, and mixing friction) is the DDT water-temperature formula, and the calculator does it in one step. The winter-specific point: with flour and kitchen both near 17°C (63°F) and a hand mix (3°C friction), the formula hands you (25 × 3) − 17 − 17 − 3, which lands at 38°C (100°F) water for a 25°C (77°F) dough. That feels uncomfortably warm on your hand, but it's correct. Don't push much past it: water well above about 40°C (104°F) stresses and slows the yeast, and from around 50°C (122°F) it starts killing it.
Where to find warmth in a cold house
You don't need a proofing box. You need a microclimate that holds 24–26°C (75–79°F) reliably.
The oven light trick
In many ovens the interior light alone (an incandescent bulb; LEDs barely warm anything) brings the cavity to roughly 24–28°C (75–82°F) with the door closed, but ovens vary a lot. Test yours: leave a thermometer in there with the light on for an hour and read the result. If it overshoots, prop the door open with a wooden spoon. If it undershoots, add a mug of just-boiled water for humidity and a few extra degrees. Tape a note to the oven controls so nobody preheats the oven with the dough inside.
Other warm spots worth checking
- On top of the fridge (compressor heat): often 22–25°C (72–77°F)
- Near (not on) a radiator: measure first, radiator surfaces run 60°C+ (140°F+)
- Inside an insulated cooler with a jar of warm water swapped every few hours
- On top of a router or cable box: can run 28–32°C (82–90°F); measure first and keep liquids away from the electronics
- Inside a switched-off microwave with a mug of hot water
The top of the fridge can be a warm, stable spot in winter, but fridges vent heat in different places. Measure first; it may be only a degree or two above the room.
Build a cheap proofer
A small seed-starting heat mat plus a plastic tub gives you a stable 25–27°C (77–81°F) environment for the price of a couple of bags of flour. Put the mat under the tub, the dough inside, lid on. It's the closest thing to professional proofing you'll get at home for very little money.
Adjusting your starter for winter
A cold kitchen slows the starter too. Three changes help:
Feed warmer water. If you've been using room-temperature water, switch to 30–32°C (86–90°F). This alone often revives a starter that "won't peak."
Use a tighter feed temporarily. If you normally feed a loose 1:5:5 (starter:flour:water), switch to a tighter 1:3:3 in winter so the starter peaks in a reasonable timeframe. The mechanics of why a tighter ratio peaks faster are in starter feeding ratios. Use it at its peak or up to 1 hour after, not 12 hours later when it has collapsed and turned acidic.
Keep it in a warm spot between feeds. Same locations as above: oven with the light on, top of the fridge, near (not on) a heat source. If a feed isn't peaking at all and you've inherited a neglected jar, reviving a forgotten starter is the faster route back than waiting it out cold.
If your starter is taking more than 8 hours to peak after feeding, it's too cold. Move it.
Adjusting bulk fermentation
This is where winter loaves go wrong. Bakers follow a 5-hour recipe in a 17°C (63°F) kitchen, shape underproofed dough, and pull a brick out of the oven.
The fix is to read the dough, not the clock. The complete set of done-signs (about 50–75% rise from when the salt went in, a domed and bubbled surface, jiggle) plus the temperature-to-time table lives in bulk fermentation by temperature, and it's worth keeping open while you bake.
Here's the winter delta on top of that guide. Using the canonical reference (about 5 hours at 24°C (75°F) with 20% levain, scaling by 2.2× for every 8°C you drop), the calculator's model puts a cold kitchen roughly here:
| Dough temp | Model estimate, bulk time (20% levain) |
|---|---|
| 24°C (75°F) | ~5 hours |
| 21°C (70°F) | ~6.5–7 hours |
| 18°C (64°F) | ~9 hours |
| 16°C (61°F) | ~11 hours |
So a recipe written for a warm kitchen can take nearly twice as long at 17–18°C (63–64°F). If you can't commit to that window, move the dough to a warm spot rather than shaping early. Rushing bulk in the cold is a direct route to dense winter loaves.
Cold bulk strategy: stretch and folds matter more
When fermentation is slow, gluten development from time alone is also slower. Front-load your structure: do 4 sets of stretch-and-folds within the first half of bulk, spaced as in that guide's fold table (about an hour apart in a dough around 18°C (64°F)), then leave the dough alone. This builds strength mechanically instead of relying on enzymatic activity that's also crawling in the cold.
Hydration in the cold
Cold dough holds its shape better than warm dough (gluten is firmer and fermentation isn't degrading it as fast), so winter is when you can comfortably run the wetter end of your range. If you usually bake at 72% in summer, 75–78% is easy to handle in a cold kitchen. The catch is the flour itself: cold winter flour and cold tap water hydrate more slowly, so give a winter dough a longer rest after mixing before you judge whether it needs more water. If you want the underlying logic of why the ratio changes how the dough feels, see hydration explained.
Cold retard considerations
Winter doesn't change retard logic much, but a few notes:
- Your fridge is still 4°C (39°F). The cold kitchen doesn't change that.
- If your shaped dough was underproofed going in (common in winter), it won't catch up much in the fridge. Retard only once bulk shows the done-signs (about 50–75% rise).
- Some bakers skip the retard entirely in winter and bake straight from a long ambient cold bulk. The flavor profile is similar. The full trade-off between the two paths is in cold retard vs same-day.
Quick comparison: warming methods
| Method | Temp range | Cost | Stability | Best for |
|---|---|---|---|---|
| Oven with light on | 24–28°C (75–82°F) | Free | Good | Bulk ferment, starter |
| Top of fridge | 22–25°C (72–77°F) | Free | Excellent | Starter, slow bulk |
| Cooler with warm water | 25–30°C (77–86°F) | Free | Fades over hours | Short proofs |
| Seed heat mat + tub | 25–30°C (77–86°F) | Low | Excellent | Everything |
| Dedicated proofer | 24–32°C (75–90°F) | High | Excellent | Heavy bakers |
| Microwave + hot water | 26–30°C (79–86°F) | Free | Fades | Final proof |
Baking the cold-fermented loaf
A winter dough behaves the same in the oven as any other; the doneness target doesn't move with the season. Pull the loaf when the center reads 96–99°C (205–210°F) on an instant-read probe; lean to the top of that range for whole-wheat or rye-heavy doughs that hold more moisture. The crumb feels gummy if you slice a still-warm loaf, so give it at least 1 hour on a rack, better a few, before cutting. Winter's slow ferment doesn't excuse a short bake.
A practical winter schedule
For a 17–18°C (63–64°F) kitchen, a workable timeline:
- 8:30: Feed starter 1:3:3 with 32°C (90°F) water and keep it in a spot that holds about 24°C (75°F)
- 14:00: Starter at peak (the model predicts about 5½ hours). Mix dough (20% levain) with warm water targeting 25°C (77°F) dough temperature, and keep it in a warm spot that holds about 25°C (77°F)
- 14:30–16:00: Four sets of stretch-and-folds at 30-minute intervals (14:30, 15:00, 15:30, 16:00)
- 16:00–about 18:30: Bulk continues until about 50–75% rise (watch the dough, not the clock). The calculator's model puts bulk at about 4.5 hours for a 25°C (77°F) dough with 20% levain
- About 18:30–19:00: Shape, into a covered banneton, into the fridge at about 4°C (39°F)
- Next morning: Preheat 60 minutes at 250°C (480°F) and bake cold from the fridge
If the dough sits in the 17–18°C kitchen instead of a warm spot, the model puts the same bulk at roughly 7½–8 hours as the 25°C (77°F) dough cools toward the room (about 9–10 hours if the dough itself starts at 17–18°C), so shaping moves to around 21:30–22:00. In a kitchen colder than 17°C (63°F), extend bulk further or move the dough to a heated environment for the entire ferment.
Common questions
Why is my starter not doubling in winter?
Most likely it's just cold. A starter at 17°C (63°F) takes about 10 hours to peak on a 1:3:3 feed, by the calculator's model, and can peak and fall back before you notice. Move it to a 24–26°C (75–79°F) spot (oven with the light on, top of the fridge, or a heat mat) and feed with 30°C (86°F) water. It does not have to double: a starter that clearly rises and domes on time is ready. If it still barely moves within 6–8 hours in the warm spot, feed it once or twice a day there for a few days. Sourdough starter not doubling has the peak times by feed ratio and temperature.
Can I bulk ferment overnight at room temperature in winter?
In a 16–18°C (61–64°F) kitchen, yes: cold already slows the dough, so you often need no change. The calculator's model puts bulk with 20% levain at about 9 h at 18°C and 11 h at 16°C. Overnight bulk fermentation gives the starter amount for an 8-, 10- or 12-hour night by kitchen temperature and says what to check in the morning.
Should I use more starter in winter to speed things up?
You can, but it's a trade-off. More levain means faster fermentation but less time for flavor development and less complex acidity. The better lever is to keep the levain percentage normal (15–20%) and raise the dough temperature instead. Only raise it if you can't find a warm spot.
My dough is cold after mixing. Can I warm it up?
Yes. Put the bowl in a slightly warm water bath, around 30°C (86°F), for 20–30 minutes to bring the dough temperature up. Don't go hotter or you'll cook the outside of the dough. Check the dough temperature again before deciding it's fixed.
Is winter sourdough actually better-tasting?
Often, if you let the slowness work for you. Long, cool fermentations build more complex acid profiles and deeper flavor. Either plan for the long timeline or warm the dough properly; mixing the two is what goes wrong.
How do I tell an underproofed loaf from one that's just dense because it was cold?
Underproofed loaves have a tight, gummy crumb with large irregular tunnels near the top crust (the dough sprang in the oven but had nothing supporting the air pockets), and they tear rather than slice cleanly. A cold-fermented but properly proofed loaf has an even, slightly tighter crumb than a summer loaf, which is normal and not a flaw. If you're chasing a dense crumb across seasons, fixing dense sourdough ranks the causes.
Let the cold set the clock
Winter baking goes wrong when you run a summer timeline in a January kitchen. Everything you need is measurable: kitchen temperature at the hour you usually mix, dough temperature within two minutes of mixing, and how long the starter takes to peak in its warm spot. Write those three numbers down once and the bulk window, the water temperature and the schedule all follow from them.