Sourdough Bulk Fermentation Time Calculator

Bulk fermentation is the first and most important fermentation stage in sourdough baking. It begins the moment you mix your dough and ends when you divide or shape it. During this time, yeast produces carbon dioxide that raises the dough, and lactic acid bacteria produce the organic acids that give sourdough its depth of flavour.

The word "bulk" refers to the fact that the entire batch of dough ferments together as one mass, before being divided into individual loaves. Getting bulk fermentation right is the single biggest factor in determining whether a sourdough loaf will have good structure, a healthy oven spring, an open crumb, and a complex taste.

Dough temperature has the biggest effect on bulk fermentation. Warmer dough ferments faster, but there is no measured rule that holds for every dough. My planning model assumes the time roughly halves for every 8°C (14°F) warmer and doubles for every 8°C cooler, so a dough that takes 8 hours at 20°C is estimated at about 4 hours at 28°C. Treat that as a working assumption for planning, and let the dough tell you when it is ready.

Dough temperature is not the same as room temperature. Friction from mixing warms the dough, and the temperature of your flour, water, and bowl all contribute. Serious bakers use a probe thermometer to measure the actual dough temperature rather than relying on ambient air temperature. The difference can be 2–4°C, which translates directly into bulk fermentation time.

20°C (68°F) → approx. 6–8 hours bulk

24°C (75°F) → approx. 4.5–6 hours bulk

28°C (82°F) → approx. 3–4 hours bulk

Starter percentage, the weight of ripe starter as a proportion of flour added to the main mix, controls how much active yeast and bacteria you introduce at mixing. More starter means more microbial activity from the start, so fermentation accelerates. My model adds roughly 40% to the bulk for each halving of the starter percentage at the same temperature. That is a planning assumption, not a measured constant.

Most sourdough recipes use between 10% and 25% starter. Lower percentages (5–10%) are common when bakers want a longer, more acidic fermentation, often overnight in the fridge. Higher percentages (20–30%) are used when baking same-day or when working in a cool kitchen where fermentation would otherwise stall.

White bread flour is usually the slowest to ferment because the bran and germ have been removed. Wholemeal flour keeps more of the wheat kernel, with more nutrients and enzymes that make sugars available to the culture. My model takes about 15% off the bulk time for all-wholemeal dough; that is a planning assumption, not a measured figure.

Rye flour behaves differently again. It contains pentosans that absorb water aggressively, a high enzyme load, and different starch behaviour, and it does not form a wheat-style gluten network. Even 10–20% rye can noticeably speed up a dough. My model takes about 30% off the bulk time at 100% rye, again as a planning assumption, and rye dough needs careful monitoring. Set the whole wheat and rye shares in the calculator to blend the effect.

The calculator gives a time range, but the final call should always be the dough itself. Experienced bakers look at four things: volume increase, surface appearance, container behaviour, and dough feel. Together these give a reliable picture of fermentation progress.

Aim for the target rise you set — usually a 50–75% volume increase. Taking the same dough from a 50% to a 75% rise stretches the bulk from 4.5–6 hours to 5.5–7.5 hours at 75°F (24°C). A flat-bottomed, straight-sided container with a rubber band at the start height makes this easy to measure. The surface should dome slightly — not be perfectly flat — and you should see small bubbles breaking through the dough. When you shake the container, the dough should wobble loosely. When you pull a small piece, it should stretch without tearing.

Under-fermented dough

Under-fermentation produces dense, tight dough that tears when shaped. The loaf has poor oven spring, a thick crust, and an overly chewy crumb. If your dough hasn't risen after the expected time, check whether your starter is active: it should reliably rise to its peak within the usual window for its ratio (for 1:1:1 I plan on 4–6 hours at 75°F / 24°C). Also check your actual dough temperature with a probe thermometer.

Over-fermented dough

Over-fermentation produces slack, sticky dough that spreads rather than holding its shape. The loaf flattens in the oven, the crust browns unevenly, and the crumb can be gummy. Once bulk is obviously over, do not try to recover it with more folding — shape immediately, skip final proof, and bake straight away or put in the fridge. Keep notes so you can adjust timing on the next bake.

Many bakers complete bulk at room temperature, then move the shaped dough to the fridge (cold retard) for 8–16 hours before baking. This gives flexibility: you can bake on your own schedule rather than when the dough demands it. The cold slows fermentation dramatically but does not stop it — a shaped loaf in a 4°C fridge is still slowly fermenting.

Because the dough keeps rising slowly in the fridge, many bakers who cold-retard end bulk earlier, at a 30–50% rise, while a counter proof needs a fuller 50–75% bulk. Choose cold retard or counter proof in the calculator and it builds the rest of the schedule — into the fridge, preheat and bake — on the clock. Some recipes instead move the bulk itself into the fridge; that slows it to a crawl, so the calculator's room-temperature times no longer apply and the dough signs become your guide.