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.
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.
- The starter must be fed at predictable intervals — irregular feeding produces an unbalanced culture where acid-tolerant bacteria outcompete yeast, producing over-sour, poorly leavening starter [VERIFY feeding schedule: daily at room temperature, weekly if refrigerated] - Temperature determines activity — a starter at 24–26°C is active and predictable; below 18°C it slows dramatically; above 32°C yeast dies before bacteria, producing acid without leavening [VERIFY temperatures] - The float test: a mature, active starter floats when a spoonful is dropped into water — the CO2 bubbles trapped in the matrix make it buoyant. A starter that sinks is under- or over-fermented [VERIFY reliability] - Starter at peak activity — the moment when it has risen to maximum volume and is just beginning to recede — is the correct moment for building the levain for bread-making - Hydration (flour-to-water ratio) of the starter affects its character: stiff starters (lower hydration) produce more acetic acid (sharper, more sour); liquid starters (higher hydration) produce more lactic acid (milder, yogurt-like sourness) [VERIFY] Decisive moment: Peak activity — the starter has risen to its maximum volume, shows a domed or slightly concave top surface, is full of bubbles throughout, and smells of ripe fruit and mild acid. This window lasts approximately 1–2 hours at room temperature before the culture begins to collapse and over-ferment.
- Irregular feeding — produces an unstable, unpredictable culture - Using chlorinated tap water — chlorine inhibits bacterial growth. Use filtered or rested water [VERIFY] - Over-sour starter — indicates acid accumulation from insufficient feeding; restore by feeding twice daily until activity recovers - Using starter past peak — over-fermented starter produces over-sour, poorly structured bread
TARTINE BREAD + MILK STREET