The Dough Handbook
Fermentation is the slow half of bread: microbes trade sugar for gas and flavour while the clock and the thermometer steer.
Baker's yeast, Saccharomyces cerevisiae, consumes simple sugars and releases carbon dioxide and ethanol. The gas inflates the bubbles the gluten network is holding; the alcohol and dozens of side compounds supply aroma. A dough is, for a few hours, a farm of single cells.
Sourdough replaces the single-celled farm with a mixed culture: wild yeasts plus lactic acid bacteria. The bacteria produce lactic and acetic acids, which lower the dough's pH, tighten its gluten, deepen flavour, and slow spoilage — the reasons sourdough keeps and tastes the way it does.
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Temperature steers everything. Yeast works slowly at refrigerator temperatures, briskly at 24–27 °C, and dies near 55 °C. Bakers exploit the whole range: a warm first rise for volume, then a cold retard overnight for flavour, since long cool fermentation builds acids and aroma that a short warm one cannot.
Time and yeast quantity trade against each other. Half the yeast roughly doubles the time; a pinch of yeast and a full day can replace a packet and an hour, with better flavour as the dividend. Recipes that promise speed simply spend yeast instead of time.
Knowing when fermentation has gone too far is a core skill. An over-proofed dough smells sharply of alcohol, shows large fragile bubbles, and a pressed finger leaves a permanent dent. Baked, it gives a pale, flat loaf — the structure was spent before the oven could set it.
Further reading