Ideal Temperature for Sourdough Bulk Fermentation

Most home bakers find 71–73°F (22–23°C) to be the sweet spot. It produces a bulk fermentation window of 5–7 hours with a strong starter at 20% inoculation — long enough to develop good flavour and structure, short enough to fit into a normal day. Below 68°F fermentation slows considerably; above 77°F it accelerates to the point where careful monitoring becomes essential.

Almost certainly a temperature difference. Recipe timings are written for a specific kitchen temperature — usually around 70–72°F. If your kitchen was warmer than that, your dough fermented faster than the recipe anticipated. A kitchen at 78°F can reach bulk completion 2–3 hours earlier than a 70°F kitchen with the same dough. This is why visual signs — not timers — are the reliable indicator of bulk completion.

Yes, but this is different from cold proofing. A fridge bulk (called retarded bulk fermentation) is possible and produces excellent flavour, but requires starting with a much shorter room-temperature bulk first — usually 1–2 hours at room temperature before transferring to the fridge for 8–16 hours. Do not skip the room-temperature phase entirely, as the dough needs some initial fermentation activity before the cold slows it down.

Under-fermented dough feels dense and tight, does not jiggle, has little surface activity, and produces a tight, dense crumb with little oven spring. Over-fermented dough is very slack and sticky, may smell strongly alcoholic or vinegary, collapses when you try to shape it, and produces a flat loaf that spreads rather than rises. When in doubt, slightly under-fermented is recoverable — slightly over-fermented is not.

Yes, generally — longer fermentation gives lactic acid bacteria more time to produce acetic and lactic acid, which increases sourness. However, the temperature also matters: cool, long fermentations tend to produce more acetic acid (sharper sourness), while warm, shorter fermentations produce more lactic acid (milder, yoghurt-like tang). If you want less sour bread, shorten your bulk and proof at a slightly warmer temperature rather than a long cold ferment.

Bulk fermentation (also called the first rise or first proof) happens before shaping, when the whole batch of dough ferments as one mass. This is where most of the flavour development happens. Proofing (the second rise or final proof) happens after shaping, when the shaped loaf relaxes and rises in the banneton. Both are essential, but bulk fermentation has a much larger impact on the final loaf structure and flavour than the cold proof does.