Techniques

How long to bulk ferment sourdough, and how to tell when it is done

Bulk fermentation is the stretch between the end of mixing and the moment you divide the dough. It is where the loaf gets its flavour, most of its volume and the gas structure that later becomes the crumb. It is also the step that bakers most often end too early, because the clock said so.

What is happening in the tub

The wild yeasts in the levain consume sugars and release carbon dioxide and alcohol. The lactic and acetic bacteria produce the acids that give sourdough its taste and, in moderation, strengthen the gluten. Meanwhile the gluten network you built during mixing keeps developing on its own, helped by the folds you give the dough and by the acids.

All of that is chemistry, and chemistry runs on temperature. Yeast activity roughly doubles for every 10 °C, so a dough at 27 °C ferments about half again as fast as the same dough at 21 °C. That is why “bulk for four hours” is not a recipe instruction so much as a guess about someone else’s kitchen.

How long it takes

Three things set the pace: dough temperature, how much levain you used, and how ripe that levain was.

Dough temperature	Levain at 20 percent of flour	Levain at 10 percent
21 °C	6 to 8 hours	9 to 12 hours
24 °C	4.5 to 6 hours	7 to 9 hours
27 °C	3.5 to 4.5 hours	5 to 7 hours

These are ranges for a white or lightly wholemeal dough at 75 to 80 percent hydration. Whole-grain doughs run faster because bran carries more enzymes and more food; a dough with 30 percent whole wheat can finish an hour earlier than the table suggests.

Dough temperature is the number that matters, and it is the one most people never measure. A thermometer in the dough at the end of mixing tells you which row of the table you are on. If you want the same result every day, aim for the same dough temperature every day and adjust the water temperature to get there.

The signs that it is done

Judge by the dough, not the clock. Look for these together:

• Growth. The dough has risen by 30 to 75 percent. The exact figure depends on the flour and on how open a crumb you want; a strong white flour can go to 75 percent, a wholemeal is safer at 40. A straight-sided container with a mark at the starting level makes this easy to read.
• Domed edges. Where the dough meets the wall of the tub, it curves upward rather than sagging. That means the gas is held by a gluten network that is still strong.
• Surface bubbles. A few bubbles on top and along the sides. Many large bubbles on top usually means it has gone too far.
• Jiggle. Shake the tub gently. The whole mass should move as one, like a set custard. A dough that sloshes has lost its structure.
• Smell. Yeasty and faintly sweet-sour. A sharp, boozy smell means the fermentation is running ahead of you.

The most reliable of these is the combination of growth and domed edges. Either one alone can mislead.

Folds during bulk

Stretch and folds, or coil folds, do two jobs: they build strength by aligning the gluten, and they even out the temperature and the gas distribution in the tub. They matter most for doughs mixed by hand or only briefly in the mixer, which come out of the mix with their gluten barely organised. A dough mixed to full development in a spiral mixer often needs no folds at all, and folding it anyway adds handling without adding strength. When folds are needed, two to four sets in the first two hours is usual, spaced 30 to 45 minutes apart, then the dough is left alone to rise. Folding late in bulk knocks out gas you will not get back.

A dough that still spreads after four folds needs more mixing next time, or a stronger flour, or less water. Folding is a correction, not a cure.

Under and over

An underfermented dough feels dense and heavy at shaping, tears rather than stretches, and bakes into a tight crumb with a pale, thick crust. It can be rescued: give the shaped loaf a longer final proof, or hold the bulk longer next time. Most dense sourdough is under, not over.

An overfermented dough is slack, sticky, and full of large bubbles; it will not hold a shape and it bakes flat with a sour, sometimes bitter taste. It cannot be rescued in the same bake. The fix is upstream: a cooler dough, less levain, or a shorter bulk.

Planning it in a production bakery

In a bakery the question is rarely “is it done” but “will it be done when I need it”. Working backwards from the oven time to the mix time, through final proof and bulk, is the whole job of the production schedule, and the temperature of the room decides the arithmetic.

A practical routine: record the dough temperature at the end of every mix, and the time bulk actually took. After two weeks you have the table above for your own bakery, your own flour and your own room, which is worth more than any table in a book.

Questions bakers ask

How do I know when bulk fermentation is done?

Look for three signs together: the dough has grown by roughly half, the edges dome up where they meet the container, and the surface shows a few bubbles and jiggles when the tub is shaken. Time alone is not a sign.

Can you bulk ferment in the fridge?

Yes, but the fridge slows fermentation far more than most people expect. Dough that goes in at 5 °C barely moves after the first two hours. A cold bulk works if the dough has already done most of its rise at room temperature, or if you give it 12 to 24 hours.

What temperature is best for bulk fermentation?

Between 24 and 27 °C for a balanced flavour. Cooler favours acetic acid and takes longer; warmer speeds everything up and pushes flavour towards lactic and milder, but leaves less margin for error.

Related

• What is autolyse, and how long should it be?. Autolyse is a rest of flour and water only, 20 minutes to an hour for most doughs, before salt and leaven go in. It shortens mixing and makes dough extensible.
• Why is my sourdough dense? Causes in order of likelihood. Dense sourdough is usually underfermented: the levain was not at peak, or bulk was cut short in a cool room. Weak flour, too much whole grain and rough shaping come next.
• Sourdough starter feeding schedule, worked back from mix time. Feed the starter so it peaks at the moment you mix. The feeding ratio and the temperature are the two timers; set them for your mix time and the schedule writes itself.

Sources: Hamelman, Bread, 3rd ed.; Robertson, Tartine Bread; Suas, Advanced Bread and Pastry. Updated 2026-09-09.