Sourdough Calculator

The algebra here exists because a sourdough starter is not a separate ingredient but a pre-mixed portion of the flour and water already in the formula. A starter at 100 percent hydration is half flour and half water by weight; more generally its flour fraction is 1 divided by 1 plus its hydration, so a 75 percent starter is 57.1 percent flour and 42.9 percent water. Since the starter contributes nothing outside those two categories, the total dough weight collapses to flour multiplied by 1 plus hydration plus salt, and the starter percentage drops out of that expression entirely. Added flour and added water are then obtained by subtracting the starter's own flour and water from the totals - skip that subtraction and a 20 percent inoculation silently pushes a 75 percent dough to nearly 80 percent. Typical working ranges are 65 to 85 percent hydration, 10 to 30 percent starter, and 1.8 to 2.2 percent salt. Inoculation sets pace rather than character: 10 to 15 percent gives long slow fermentation and more acetic tang, 25 to 30 percent ferments quickly and tastes milder. The culture itself is a stable partnership of lactic acid bacteria and wild yeasts at roughly a hundred bacteria per yeast cell, dropping dough pH from about 6 toward 3.5 to 4.5. Fermentation estimates should be treated as rough guides, since rates roughly double for each 8 to 10 degrees C of warming, whole grain and high-protein flours absorb more water than white flour, and an underfed starter simply will not perform at its nominal percentage.

Sourdough is the original leavening. Every risen bread before the late nineteenth century relied on a maintained culture or on barm from brewing, and the technique is documented across ancient Egypt and the classical Mediterranean. It receded quickly once Fleischmann-style compressed baker's yeast became available from 1868 onward, since a single-strain yeast rises dough in hours rather than most of a day and requires no daily feeding. Sourdough survived mainly in regional traditions - German and Nordic rye breads, Italian panettone, and the bakeries of San Francisco, where the term itself became a nickname for Gold Rush prospectors who carried their cultures with them. The scientific description came much later. In 1971, researchers at the USDA Western Regional Research Center working on San Francisco bread isolated and named the dominant bacterium of that culture, Lactobacillus sanfranciscensis, and described its symbiosis with an acid-tolerant wild yeast that ferments maltose poorly and so leaves it to the bacteria. That work explained why a starter is stable over years of feeding rather than being overrun by contaminants. The modern revival is a publishing and internet phenomenon: baker's-percentage formulas circulated on baking forums from the early 2000s, and Chad Robertson's Tartine Bread in 2010 turned high-hydration naturally leavened loaves into a mainstream home project, which is when calculators of this kind became widely used.