Cold proof sourdough in the fridge for 12 to 16 hours — overnight is the sweet spot. Anywhere from 8 to 24 hours at 3–5°C works well: go shorter for a milder loaf, longer for a tangier crumb and deeper flavour. Push past 24 hours and you risk over-proofing, particularly with wholegrain flour or a very active starter. When in doubt, 14 hours in a standard home fridge is a superb default.

The ideal cold proof, by the numbers

  • 8–10 hours: mild flavour, gentle sourness — good for sandwiches and fussy eaters
  • 12–16 hours: the sweet spot — balanced tang, open crumb, maximum convenience (shape in the evening, bake in the morning)
  • 18–24 hours: pronounced sourness and complex flavour; works best with strong white flour
  • 24–36 hours: risky territory — possible with a stiff, young levain and cold fridge, but expect a denser crumb

These ranges assume your fridge sits at 3–5°C, which is where most UK fridges land. A fridge running warm (7–8°C) ferments noticeably faster — worth checking with a cheap fridge thermometer if your timings keep going awry. Flour matters too: wholemeal and rye ferment faster than white because of their higher enzyme activity, so shave a few hours off for wholegrain loaves.

Why cold proof at all?

Retarding the dough in the fridge — the technical term for a cold proof — does three genuinely useful things. First, flavour: the cold slows yeast activity more than bacterial activity, so lactic and acetic acids build up relative to CO₂, giving that characteristic sourdough tang. Second, scheduling: it decouples baking from your day — shape at 9pm, bake at 9am, no 4am alarms. Third, handling: cold dough is firmer, scores more cleanly with a lame, and often gets better oven spring because it hits the hot Dutch oven chilled.

It is not mandatory — you can proof at room temperature for 3–5 hours and bake the same day — but the cold proof is what separates decent homemade sourdough from bakery-quality loaves. If you are just getting your culture going, see how to dehydrate sourdough starter for keeping a backup of your precious starter.

How to cold proof sourdough, step by step

  1. Bulk ferment first. Complete your room-temperature bulk fermentation as normal — the dough should be risen, jiggly and full of bubbles.
  2. Shape tightly. A taut surface tension helps the loaf hold its shape during the long cold rest.
  3. Flour a banneton generously with rice flour (it resists sticking far better than wheat flour) and place the loaf seam-side up.
  4. Cover well. A shower cap, plastic bag or damp tea towel stops the surface drying out and forming a skin.
  5. Refrigerate at 3–5°C for 12–16 hours. Put it towards the back where the temperature is most stable, away from the door.
  6. Bake straight from the fridge. Do not let it warm up — turn it out, score, and get it into a preheated Dutch oven or onto a baking stone immediately. The thermal shock boosts oven spring.

Can you cold proof for too long?

Yes — over-proofing is the main failure mode. Signs your dough went too far:

  • It spreads flat instead of holding its shape when turned out
  • The surface looks slack, wrinkly or slightly collapsed
  • It feels fragile and tears when scored
  • The baked loaf is dense with a gummy crumb line at the bottom

The usual culprits are a very active starter, a warm fridge, or high wholegrain content. If your loaves keep over-proofing at 16 hours, try 10–12, use your starter a little younger (just past peak rather than well past), or nudge the fridge colder. Slightly under-proofed beats over-proofed every time — an under-proofed loaf still springs in the oven, while an over-proofed one has nothing left to give. Bagels follow similar fermentation logic; see how long bagels are good for once baked.

The poke test, cold edition

Straight from the fridge, gently flour a fingertip and press the dough about 1cm deep:

  • Springs back immediately: under-proofed — give it more time (or a brief room-temperature finish)
  • Springs back slowly, leaving a slight indent: ready — preheat and bake
  • Indent stays put: over-proofed — bake it anyway (it will still taste good as toast), but shorten the proof next time

Cold dough springs back more slowly than warm dough, so judge conservatively — a slightly slow spring-back on cold dough usually means “ready”, not “over”. With a few bakes you will calibrate to your own fridge, flour and starter, and the whole process becomes gloriously routine.

Fitting the cold proof into your schedule

One of the quiet joys of the cold proof is how it bends to your timetable rather than the other way round. Shape at 8pm and bake at 10am for a 14-hour retard; shape at lunchtime and bake the next morning for 20 hours of deeper flavour. If your morning runs away from you, the dough will happily sit until lunchtime — a 16-hour proof becoming 19 hours is rarely a disaster with white flour.

The one thing to avoid is stacking uncertainties: a new starter, a new flour and a 22-hour proof all at once. Change one variable at a time, keep notes on timings that worked, and within a month you will have a house routine that produces consistent loaves on autopilot.

For a solid foundational method, the BBC Good Food sourdough recipe pairs well with an overnight cold proof.

Sourdough dough in a floured banneton basket inside an open fridge
Twelve to sixteen hours at 3–5°C gives balanced flavour — then bake straight from the fridge.

FAQs

Do you cover sourdough in the fridge during cold proof?

Yes, always. An uncovered loaf dries out, forming a thick skin that restricts oven spring and looks dull. A shower cap or plastic bag is ideal; a damp tea towel works too.

Can you cold proof sourdough for 48 hours?

Not recommended for standard dough — it will almost certainly over-proof. Very stiff, low-hydration doughs with young starters can survive 36 hours in a cold fridge, but 48 is pushing your luck.

Should sourdough go straight from the fridge to the oven?

Yes. Cold dough scores cleanly and gets a burst of oven spring from the temperature contrast. Letting it warm up first makes it slack and harder to handle, with no flavour benefit.

What temperature should the fridge be for cold proofing?

Between 3°C and 5°C — standard fridge temperature. Below 2°C fermentation nearly stops; above 7°C it runs fast enough to risk over-proofing overnight.