Starter culture

A starter culture is a concentrated batch of live microorganisms, usually bacteria, yeast, or both, that is added to a new batch of food or drink to kick off fermentation reliably. Sourdough starter, yogurt starter cultures, and kefir grains are all examples, each suited to a different kind of ferment and food base.

Starter cultures generally come in two forms, direct-set cultures that are used once and not reused, and ongoing or heirloom cultures like a sourdough starter or kefir grains that are maintained indefinitely by regularly feeding them fresh food. Ongoing cultures need a consistent feeding schedule to stay active, while direct-set cultures are simpler but require buying or making a fresh batch each time.

A common beginner mistake is letting an ongoing culture run out of food for too long, which can weaken or, in some cases, kill it off entirely. Storage conditions also matter a lot, since some cultures tolerate refrigeration between uses while others are best kept at room temperature and fed daily. Reading the specific care instructions for whichever starter you are using, rather than assuming all starters behave the same, avoids most common failures.