Sourdough Bread

What it is

Sourdough is bread leavened not by commercial yeast but by a starter — a living culture of wild yeasts and lactic-acid bacteria maintained in a flour-and-water medium. The result is a crusty, open-crumbed loaf with a characteristic tang, a long keeping quality, and a flavor shaped by time and microbial life.

How it's made

A baker keeps a starter (also levain, chef, or mother) — flour and water colonized by wild Saccharomyces and other yeasts plus Lactobacillus bacteria — feeding it to keep it active. A portion is mixed into the dough, which then ferments slowly over many hours: the yeasts produce carbon dioxide to leaven the loaf while the bacteria produce lactic and acetic acids for sourness and keeping power. The dough is typically autolysed, bulk-fermented with periodic folds, shaped, proofed in a banneton, scored, and baked — often in a covered Dutch oven to trap steam for a blistered, crackling crust.

Flavor profile

Tangy and complex, ranging from mild and milky to sharply sour depending on the culture, hydration, and fermentation time; the crust is deeply browned and crackling, the crumb chewy and open with a custardy interior. Flavor is the product of fermentation chemistry as much as ingredients.

Culinary uses

Eaten as table and sandwich bread; in San Francisco it is the traditional vessel for clam chowder served in a hollowed bread bowl. The long fermentation is also valued for making bread more digestible.

Regional variations

San Francisco sourdough is the most famous regional style, associated with a distinctly tangy loaf and historic bakeries dating to the Gold Rush (Boudin Bakery, established 1849, claims a continuous mother starter since). The Lactobacillus sanfranciscensis bacterium is named for the city — fueling a romantic "terroir" argument that the local microclimate produces a uniquely sour bread. The honest scientific picture is more nuanced: that bacterium is now known to occur in sourdough cultures worldwide, so San Francisco's distinctiveness owes as much to its baking traditions and history as to any exclusive local microbe. Beyond it lie many regional and national sourdough traditions — German and northern European rye sourdoughs, Italian pane styles, and others — each shaped by local flours and cultures.

Cultural & historical context

Sourdough is the oldest form of leavened bread, predating commercial yeast by millennia; leavening by wild fermentation was known in ancient Egypt and was the universal method until industrial yeast arrived in the 19th century. It carries frontier romance in the American West — Gold Rush prospectors who kept a starter alive were nicknamed "sourdoughs" — and it has enjoyed a powerful modern artisan revival, driven by bakers like the Tartine school and by a worldwide home-baking boom (notably during the 2020 pandemic), when keeping and naming a starter became a small cultural phenomenon of its own.

Reference notes

Tags: fermented, bread, wild-leavened, artisan, vegan-base. Related ingredients: bread flour, rye flour, whole wheat flour, starter culture, sea salt. Related cuisines: American (San Francisco), German, European, global artisan. Suggested Cuisinopedia links: Bread Flour, Rye Flour, Levain, Kimchi (fermentation kinship). Find-it note: high-protein bread flours, rye, and bannetons are stocked at baking-supply and specialty markets; an established starter can be sourced from a local bakery or maintained from scratch.

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