A sourdough starter is a living culture of wild yeasts and lactobacilli, maintained with regular flour-and-water feedings. It serves as the sole leavening agent in true sourdough bread, producing both rise and the characteristic tang. For active use, a typical feeding ratio is one part starter to five parts flour and five parts water by weight, which produces a slow, full peak roughly eight to twelve hours after feeding at around 24°C. A starter is ready to bake with when it at least doubles within four to eight hours of feeding, smells fruity or yogurty rather than vinegary, and passes the float test — though a thick starter can float even when under-active, so rise speed and smell remain more reliable. The peak of a starter's rise is the highest point just before it begins to fall; it is at peak or just past peak, "ripe," that the starter is best incorporated into dough for predictable fermentation. For a 1:5:5 feeding, the starter can still be used one to two hours past peak, but longer and the gluten begins to weaken; refrigerating overnight after peak is a common way to hold it for next-day use.
A healthy starter smells yeasty, fruity, slightly tangy, and yogurty. A dark watery layer on top, called hooch, indicates the starter is hungry — it can be stirred back in, followed by a fresh feeding, or poured off if very old. A vinegar or nail-polish smell points to over-acidity or contamination and calls for repeated feedings to reset the culture. To build a starter from scratch, mix 50 grams of whole rye flour with 50 grams of water in a jar, rest it for 24 hours, then discard half and feed it 1:1:1 daily; active bubbles usually appear between day three and day seven. Whole rye is preferred for new starters because it carries more wild microbes and nutrients than all-purpose flour. A young starter, only hours past feeding, gives mild CO₂ production with less acid, while a mature starter aged six to twelve hours at room temperature reaches peak activity with a balanced acid profile. Ideal ambient temperature for an active starter is 24–26°C; warmer conditions speed fermentation and increase acidity, cooler conditions slow it and yield milder flavor.
For storage, a starter kept at room temperature in a sealed jar will last a few days between feedings, while long-term storage is best in the fridge at a 1:5:5 ratio refreshed weekly. For multi-month storage, the starter can be dehydrated by spreading it thin on parchment until dry, then crumbled and stored in a jar — rehydration with fresh water and flour brings it back when needed, a useful travel-proofing method. Freezing also works well: feed the starter strong, let it reach peak, then freeze in small portions like ice cube trays, thawing and feeding twice before use. To refresh a neglected starter, discard most of it and feed 1:2:2 every 12 hours at room temperature; within two to three days it should be active again, signaled by a sweet fruity smell. Starter discard need not go to waste — it enriches pancakes, waffles, crackers, pizza dough, banana bread, fried discard crackers, or any dough as a small flavor-boosting pre-ferment, though discard is less active than ripe starter and is not strong enough to leaven bread on its own.