Bulk fermentation is the primary flavour-building stage of sourdough bread — the long fermentation of the entire dough mass after mixing, during which yeast produces CO2 (structure) and bacteria produce acid (flavour). Robertson's contribution was teaching bakers to read the dough's progress rather than rely on time alone — the dough tells you when it is ready.
The period between mixing and dividing/shaping during which the entire dough mass ferments at room temperature. The dough is stretched and folded at intervals to develop gluten structure and redistribute fermentation gases.
- Target temperature of 24–26°C for the bulk ferment — this temperature produces the most reliable, predictable activity. Cooler temperatures slow fermentation and produce more acetic acid (sharper flavour); warmer temperatures speed fermentation and produce more lactic acid (milder, more complex flavour) [VERIFY temperatures and flavour effects] - Stretch and fold sets every 30 minutes for the first 2 hours — this develops gluten structure and redistributes the CO2 produced by yeast. Without folding, the dough develops poor structure and the gas escapes unevenly [VERIFY timing] - Visual cues at the end of bulk fermentation: dough has increased in volume by 20–30%, feels airy and jiggly when the container is shaken, shows bubbles throughout, dough surface is domed rather than flat, dough released from the container shows a network of gas bubbles [VERIFY volume increase] - Time is an indicator, not a rule — bulk fermentation takes 3–5 hours at 26°C but can take 8–12 hours in a cool kitchen. The visual and tactile cues override the clock Decisive moment: The jiggle test — when the container is shaken gently, the dough should wobble and jiggle as a unified mass, showing that gas has been trapped throughout. Under-fermented dough is dense and doesn't jiggle. Over-fermented dough is slack, smells of alcohol, and has lost the ability to hold its structure.
TARTINE BREAD + MILK STREET