Sourdough starter

What it is

A starter (Italian lievito madre or pasta madre) is a stable colony of wild yeasts and lactic-acid bacteria living in a flour-and-water paste. The yeasts leaven; the bacteria produce the acids that give sourdough its tang and help it keep longer. Once established and fed, one starter can leaven bread indefinitely.

Compared with commercial yeast it works more slowly and unpredictably, which is a feature: the long ferment builds deep flavor and an open, custardy crumb in focaccia.

Keeping it healthy

A starter needs regular feeding — discarding most of it and refreshing with fresh flour and water. Kept at room temperature it wants daily feeding; kept in the fridge it can go a week or more between feeds, which suits occasional bakers. Feed it once or twice to wake it up before a bake day.

A healthy starter smells pleasantly sour, yeasty, and a little fruity, and rises predictably after feeding. A thin layer of grey liquid ("hooch") just means it is hungry — stir it in or pour it off and feed.

Knowing when it is ready to bake

Use the starter at its peak: several hours after feeding, when it has risen to roughly double, domed, and is full of bubbles but has not yet started to collapse. The classic float test — a spoonful floats in water — is a rough readiness check.

Baking with a sluggish, hungry, or over-ripe starter is a common reason sourdough focaccia rises poorly or tastes sharply sour. Time your feed so the starter peaks when you want to mix.

Using it in focaccia

Sourdough focaccia typically uses the starter as the sole leavening, with a long bulk ferment (often partly in the fridge). Expect timings measured in many hours rather than one or two. The reward is a focaccia with more flavor complexity, a chewier open crumb, and a longer shelf life. You can also hedge with a small amount of commercial yeast alongside the starter for a more predictable rise.