There's a particular email we get every January. It usually starts with: "My sourdough has stopped working." The starter that bubbled like a science experiment in October is now flat and sour-smelling. The boule that came out of the oven beautifully in September is dense and gummy in February. The recipe didn't change. The kitchen did.
If you're baking in Canada, the northern US, or anywhere else with real winters, this guide is the thing we wish someone had handed us our first cold-weather year. None of it is complicated. All of it is the difference between bread that works and bread that doesn't.
The three things that actually change in winter
Almost every winter sourdough problem traces back to one of three things, sometimes all three at once.
1. Your kitchen is colder than you think
Most published sourdough recipes are written assuming a 24°C / 75°F kitchen. That's a sunny afternoon in May. A typical Canadian kitchen on a January morning runs 18 to 21°C, and the counter near an exterior wall — where most of us mix dough — can be 16 or 17°C.
Sourdough fermentation is enzymatic and microbial, and both slow dramatically as temperature drops. A bulk fermentation that takes 4 hours at 24°C can take 7 to 9 hours at 19°C. If you're following a clock instead of looking at your dough, you'll under-bulk every loaf you bake from October through April.
2. Indoor humidity has fallen off a cliff
In summer most Canadian homes sit at 50 to 60% relative humidity. In winter, with the heating running and outdoor air drier than the Sahara, indoor RH crashes to 20 to 30%. In Edmonton or Winnipeg in January, it can drop below 20%.
Dry air pulls moisture out of dough at every stage — autolyse, bulk, shaping, proofing. The 75% hydration boule you mixed in July will feel like 71% in February. The dough surface will skin over while you're not looking. Pre-shaped loaves will dry out on the bench.
3. Your starter has slowed down
The microbes in a sourdough starter are the same year-round, but their metabolism is climate-dependent. A starter kept on a 24°C counter doubles in 4 to 6 hours; the same starter kept on a 19°C counter can take 9 to 12. If you're feeding once a day and waiting for it to peak, in winter you might be feeding it before it's actually peaked — slowly weakening the culture each cycle.
The fixes — none of them require buying anything
Treat your dough by sight, not by clock
This is the single most useful change you can make. Recipes that say "bulk for 4 hours" are giving you a guideline that assumes summer conditions. What you actually want is a dough that has grown by 50 to 70 percent, looks softly domed, has visible bubbles forming at the edges, and feels gassy when you tilt the bowl. That state is the goal — whether it takes 4 hours or 8.
Mark the side of the bowl with a rubber band at the starting volume. Check at the 4-hour mark. If it hasn't moved much, give it more time. The fridge is your friend if you need to go to bed.
Bump hydration by 2 to 4%
If your summer recipe is 75% hydration (i.e., 375 g water per 500 g flour), in deep winter try 77 to 79% (385 to 395 g). That extra 10 to 20 grams compensates for what the dry kitchen pulls out and gives you the dough texture you remember from August.
Cover dough more aggressively
One layer of plastic isn't enough in a 25% RH kitchen. Cover the bowl with both a damp tea towel and plastic wrap. For a banneton, slide it inside a plastic bag in the fridge — the cold proof in winter is fine, but exposure to dry air ruins the surface. Pre-shaped loaves on the counter need to be covered immediately, not after you finish shaping the others.
Build a proofing box from things you already own
The simplest proofing box: an oven that's been off all day, with the interior light bulb turned on. Most ovens hold around 24 to 27°C with just the light on, which is exactly the temperature dough wants. Bulk fermentation in there will run on the recipe's stated timeline.
A second option, just as good: a microwave with a mug of just-boiled water sitting inside next to your bowl. Close the door. The water creates humidity and warmth as it cools. Replace the water every 90 minutes if you're bulking longer than two hours.
If you want a more permanent setup, a $30 seedling heat mat under the bowl with a thermometer beside it works beautifully and is what serious home bakers we know in Calgary use through their long winters.
Feed your starter twice a day
In winter, switch to feeding twice a day if your starter feels sluggish. A morning feed and an evening feed gives the microbes more frequent food and keeps the culture peaking before it crashes. Use a 1:2:2 ratio in winter (one part starter, two parts water, two parts flour) instead of 1:1:1 — more food per feed compensates for slower metabolism.
Find the warmest spot in the house for the starter jar. The top of the fridge is usually 2 to 3 degrees warmer than the counter. So is the corner of a kitchen near a router or modem. So is a high shelf above a baseboard heater. So is the cabinet directly above the dishwasher when it's running.
Use cold-proofing strategically
The fridge is the great equalizer. A 12 to 18 hour cold proof slows fermentation enough that imprecise bulk timing in winter still gives you a great loaf. Shape, into a banneton or pan, into the fridge for 14 hours, bake straight from cold. Easier and more forgiving than trying to time a same-day proof in a 19°C kitchen.
Regional notes
Vancouver and the Pacific Northwest: you have it easier than the rest of the country. Winters stay mild (5 to 10°C outdoors), indoor humidity holds at 50 to 60%, and your kitchen rarely drops below 20°C. You can essentially ignore most of this guide and run summer recipes year-round.
Toronto, Montreal, Ottawa, southern Ontario and Quebec: classic cold-and-dry. Indoor humidity 25 to 35%, kitchen temperatures 19 to 21°C. The advice in this guide was written with you in mind. Bump hydration 3%, use a proofing box, feed your starter twice a day, and you'll bake great bread all winter.
Calgary, Edmonton, Winnipeg, the Prairies: the hardest sourdough conditions in the country. Indoor humidity can drop below 20%, and your kitchen counter near an exterior wall might be 15°C in February. You need every fix in this guide — proofing box mandatory, hydration up 4 to 5%, plastic-and-towel cover at all times. Calgary's altitude (1,045 m) is real but minor: reduce starter by 10% and add a touch more water; otherwise the recipes work as written.
Atlantic Canada: the maritime air keeps humidity higher than the Prairies but the winter is long. Treat it like Toronto — mid-range conditions, mid-range adjustments.
Northern US (anywhere with real winters — Minnesota, Wisconsin, Michigan, Maine, Vermont, etc.): conditions match southern Canadian provinces closely. This guide applies cleanly. Use Canadian flour adjustments if you happen to bake with imported Canadian flour; otherwise stay with King Arthur, Bob's Red Mill, or your favourite mid-protein bread flour.
When to give up and start a fresh starter
Sometimes a starter is genuinely sick, not just cold. Signs that it's time to start fresh: persistent off-smells (acetone, vinegar, anything actively unpleasant beyond a mild yeasty tang); pink, orange, or fuzzy growth on the surface; a hooch (the dark grey liquid that forms on top) that won't go away even with regular feeding; no rise after a week of twice-daily feeds with the proofing-box treatment.
A fresh starter takes 7 to 10 days to come online from scratch — 50 g rye or whole wheat flour and 50 g water, mixed and left at room temperature, fed once a day, until it shows reliable bubbles and rises. There are good guides everywhere on the internet for this. The point is: don't keep nursing a starter that's failed. Wave it goodbye and start again. It happens to everyone.
Common questions
Why does my sourdough rise more slowly in winter?
Because the kitchen is colder than the recipe assumes. Most published recipes assume 24°C; a typical Canadian or northern-US winter kitchen sits at 18 to 21°C. Yeast and bacterial activity drops sharply with temperature — bulk that takes 4 hours in summer can take 7 to 9 in winter. The fix is patience, not panic.
How do I keep sourdough starter alive in a cold kitchen?
Find the warmest spot in your home (top of fridge, near a router, oven with light on). Feed twice a day in winter rather than once. If your starter is sluggish for more than 48 hours, switch to a 1:2:2 ratio for stronger feeds.
Should I add more water to my dough in winter?
Yes — usually 2 to 4% more water. Indoor humidity in winter drops to 20 to 30%, and dry air pulls moisture out of dough during bulk and shaping. The dough you mix at 75% hydration in summer feels like 71% in February.
What's a proofing box for sourdough?
Any enclosed warm space at 24 to 27°C. The simplest is an unheated oven with the light on. A microwave with a mug of just-boiled water inside also works. Both cost nothing.