Levain

Levain is a natural leaven used in bread making, created by fermenting flour and water with wild yeasts and lactic acid bacteria. It serves as a microbial starter that, when added to dough, provides leavening through gas production and contributes complex aromas and flavors beyond those produced by commercial yeast alone.

The leavening action arises from a symbiosis of yeasts and lactic acid bacteria. Yeasts produce carbon dioxide that leavens the dough, while lactic and acetic acids from the bacteria contribute acidity, aroma, and a distinctive crumb texture. The balance of microorganisms, and thus flavor and rise, is influenced by factors such as hydration level, temperature, flour type, and feeding regimen.

Levain is typically maintained by regularly feeding a portion of the starter with fresh flour and water to keep it active. It can be kept at room temperature for daily baking or refrigerated for longer intervals, with periodic feedings to refresh the culture. Levain can be stiff (lower hydration) or liquid (higher hydration), and its hydration level affects fermentation rate, acidity, and flavor development. Rye and whole-grain flours are common in levains because they often foster robust microbial activity.

To use levain in a recipe, a portion of the mature levain is mixed into dough dough to inoculate fermentation. The levain’s maturity, demonstrated by a consistent rise and aroma, signals readiness to bake. Safety practices include discarding any levain that shows mold, unusual color, or off odors. Etymologically, levain means leaven in French and is synonymous with sourdough in many baking contexts.