Sourdough Starter: The Living Culture

Chad Robertson's Tartine Bread codified the natural leavening method for a generation of bakers — presenting sourdough not as an ancient mystical process but as a precise, manageable biological system. The wild yeast and bacteria culture (levain) that leavens Tartine bread is maintained through daily feeding, and its health is the single most important variable in the final bread. Robertson's documentation made the process reproducible for non-professional bakers.

A culture of wild yeast (primarily Saccharomyces cerevisiae and related strains) and lactic acid bacteria (primarily Lactobacillus species) maintained in a flour-water matrix through regular feeding. The yeast provides leavening (CO2 gas production); the bacteria provide flavour (lactic and acetic acid). The ratio between the two organisms determines the bread's flavour character.

• Ethiopian injera starter (teff-based wild fermentation — same wild yeast and bacteria, different grain), German Sauerteig (same organism, stiffer hydration — more acetic, sharper), San Francisco sourd

The starter's flavour directly enters the bread — a mild, ripe starter produces a mildly complex loaf; a sharp, over-sour starter produces an aggressively acidic loaf. The flavour of the bread is built in the culture before the dough is even mixed. This is why controlling the starter is the most important skill in sourdough baking.