Leavened bread via wild fermentation dates to ancient Egypt circa 3500 BCE; sourdough as a named tradition formalised in San Francisco Gold Rush era, 1840s–1850s
A sourdough starter is a living culture of wild yeasts and lactic acid bacteria (LAB) maintained in a flour-and-water medium, capable of leavening bread and imparting complex flavour through organic acid production and protease activity. Building a wild starter from scratch harnesses the microbial ecology of flour, water, and the baker's environment — different locations, flour mills, and water chemistry produce genuinely distinct starter profiles. The establishment process typically takes 7–14 days. Initially, diverse microorganisms colonise the fresh flour-water mixture, producing erratic and often foul-smelling fermentation as heterogeneous bacteria compete. As the baker begins regular feeding — discarding a portion and adding fresh flour and water — conditions are shaped toward a stable pH (approximately 3.5–4.0 after peak activity) that selects strongly for acid-tolerant wild yeasts (primarily Kazachstania humilis, formerly Candida humilis) and heterofermentative LAB (Lactobacillus sanfranciscensis being the most studied). This succession — from chaotic to stable — takes 7–10 days of regular feeding. Hydration ratio (the ratio of water to flour by weight) determines starter consistency and flavour character. 100% hydration (equal weight flour and water) produces a pourable, active starter with moderate acidity. Lower hydration (60–70%) creates a stiff starter with higher acidity and different yeast-LAB ratios. Many bakers maintain a liquid 100% hydration starter for everyday use and a separate stiff 65% levain for specific bread applications. Once established, a starter requires regular feeding to remain active. At room temperature (22–24°C), a 1:1:1 ratio (starter:flour:water by weight) fed once or twice daily maintains peak activity. Refrigeration slows metabolism, allowing weekly feeding. Before use in a recipe, the starter must be fed and allowed to peak — typically doubling to tripling in volume — at which point yeast activity and LAB acid production are at their highest.
Produces complex sour, tangy, and mildly funky flavour — acidity profile (lactic vs acetic) controlled by hydration, temperature, and timing relative to peak
Whole grain flours (whole wheat, rye) establish wild starters faster due to higher wild yeast and bacteria populations on bran Regular feeding at consistent ratios selects for a stable, predictable microbial community over 7–14 days The float test (does a spoonful float?) indicates gas production but not overall health — timing from peak is more reliable Refrigerated starters can be fed weekly but must be brought to room temperature and fed 1–2 cycles before use Hydration ratio affects microbial balance: lower hydration favours acetic acid production (sharper); higher hydration favours lactic acid (milder, more yoghurt-like) A mature starter should double or triple within 4–8 hours of feeding at 22–24°C — this is readiness for use
Mark the jar with a rubber band at the peak feeding level to clearly track rise and fall between feedings For consistent bread results, feed at the same time each day so you know exactly when the starter peaks relative to your schedule Maintain a second backup starter in the freezer — dried starter flakes or frozen spoonfuls can be revived after months of inactivity Whole rye flour fed 1:1:1 will produce a dramatically active starter within 24–48 hours of feeding once mature For maximum sour flavour, use the starter at or just past peak and incorporate a longer, cooler bulk fermentation in the final dough
Using chlorinated tap water which inhibits wild yeast and bacteria — use filtered or left-to-stand water Not discarding before feeding, causing accumulated acidity to drop below functional range for yeast activity Judging readiness by smell alone in the early days — the first week's smell is often unpleasant and misleading; wait for maturity Refrigerating a new, immature starter before it has fully established — cold storage requires a stable culture first Using only white flour when building — whole grain rye accelerates establishment significantly due to higher wild microbe loads