Sourdough Starter Calculator

A sourdough starter is a stable co-culture, typically dominated by wild yeasts and heterofermentative lactic acid bacteria in a rough ratio near 100 bacteria to every yeast cell. It is described by two numbers. Hydration is water weight divided by flour weight times 100, so a 100 percent starter carries equal flour and water and behaves like thick batter, while a 50 percent stiff starter ferments more slowly and pushes the acid balance toward acetic sharpness. Refresh ratio, written as seed to flour to water, sets how much fresh substrate each cell receives: at 1:5:5 the seed is one part in eleven, so a 200 gram build takes about 18 grams of seed with 91 grams each of flour and water. Temperature is the dominant rate variable. Near 27 degrees C a well-fed starter peaks in roughly 4 to 6 hours, near 21 degrees C it needs 6 to 10, and below 16 degrees C it can take 14 hours or more, which is why an unchanged ratio behaves differently in summer and winter. Readiness is judged by volume doubling, a domed and visibly bubbled surface, and the float test. The caveats are that peak-time estimates are approximations sensitive to flour ash content and culture maturity, that larger refresh ratios delay the peak while producing milder flavor, and that hooch, the dark liquid layer that forms on a neglected starter, signals exhausted food rather than a dead culture.

Leavening by wild fermentation is among the oldest food technologies, with evidence of leavened bread in ancient Egypt several thousand years ago and continuous use across the Mediterranean and Near East long before anyone knew why dough rose. The mechanism stayed unexplained until Louis Pasteur established during the 1850s and 1860s that fermentation is the work of living microorganisms, which opened the way to isolating and selling single-strain yeast. Fleischmann began marketing compressed baker's yeast in the United States after 1868, and commercial yeast steadily displaced natural leaven in industrial bread. Sourdough survived as a regional and artisan practice, most famously in San Francisco, where bakers maintained cultures continuously from the Gold Rush era onward. Scientific description came much later: researchers working with San Francisco sourdough in the early 1970s characterized the distinctive bacterium responsible for its flavor, which was subsequently named Lactobacillus sanfranciscensis. The precise weight-based vocabulary this calculation uses, hydration percentages and colon-separated refresh ratios, comes from baker's percentage, the milling and baking industry convention of expressing every ingredient as a percentage of flour weight. Artisan bakers carried that notation into home practice during the sourdough revival of the 1990s and 2000s, which is why maintenance is now discussed in grams and ratios rather than in cups and vague daily feedings.