San Francisco Sourdough

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.