San Francisco sourdough — a bread leavened entirely by wild yeast and *Lactobacillus sanfranciscensis* (a species of lactic acid bacteria literally named for the city), with a thick, crackly crust and a distinctly tangy crumb — is America's most famous bread and the product of a specific microbial terroir. The sourdough tradition in San Francisco dates to the Gold Rush (1849), when Isidore Boudin, a French baker, began making sourdough using wild cultures. The Boudin Bakery has operated continuously since 1849, and the "mother" starter (the living sourdough culture maintained through regular feeding) is claimed to be the same culture Boudin used. The specific tang of San Francisco sourdough is produced by *L. sanfranciscensis* and the wild yeast *Candida milleri*, which thrive in the city's cool, fog-damp climate.
A round boule or long batard of bread with a thick, deeply crackled crust (dark golden to mahogany), a moist, open crumb with large, irregular holes, and a distinctly sour, tangy flavour. The tang should be pronounced but not overwhelming — a balance of acetic acid (sharp, vinegary) and lactic acid (milder, yogurt-like). The crust should be thick enough to crackle audibly when torn. The interior should be moist, slightly chewy, and aromatic.
1) The starter is everything — a mature, active sourdough starter maintained through daily feeding. The starter provides both leavening (wild yeast) and flavour (lactic and acetic acid from bacterial fermentation). 2) Long, cold fermentation — the dough rises slowly in the refrigerator for 12-48 hours. The cold slows the yeast (preventing over-rising) while allowing the bacteria to continue producing acid (increasing the tang). 3) High hydration dough (70-80%) — the wet dough produces the open crumb with large holes. 4) Steam in the oven during the first 15 minutes — steam delays crust formation, allowing maximum rise (*oven spring*), then the crust sets and crisps as the steam dissipates. A Dutch oven traps steam effectively. 5) Bake at 230°C+ — the high heat produces the thick, deeply coloured crust.
Boudin Bakery's bread bowls — hollowed-out sourdough rounds filled with clam chowder at Fisherman's Wharf — are the tourist experience that is also a genuinely good format. The sourdough absorbs the chowder; the bread bowl is eaten as the final course. The "can you replicate SF sourdough elsewhere?" debate: the specific *L. sanfranciscensis* strain is unique to the Bay Area's climate. Bakers elsewhere can make excellent sourdough, but the specific tang profile of a Boudin loaf is, to some extent, terroir-dependent.
Immature starter — a starter that hasn't been regularly fed and maintained produces weak leavening and poor flavour. Under-fermenting — the tang develops during fermentation; a short rise produces bland bread. Not enough steam — the crust stays pale and thin.
Chad Robertson — Tartine Bread; James Beard — American Cookery