Lactobacillus sanfranciscensis (formerly L. sanfrancisco) is a species of lactic acid bacteria that helps give sourdough bread its characteristic taste. It is named after San Francisco, whose sourdough was found to contain the variety, though it not exclusive to the area.
Sourdough starters are leavened by a mixture of yeast and lactobacilli in a ratio of about 1:100. The yeast is most commonly Candida milleri. This yeast cannot metabolize the maltose found in the dough, while the Lactobacillus needs maltose. They therefore act without conflict for substrate, with the Lactobacillus utilizing maltose and the yeast utilizing the other sugars, including the glucose produced by the Lactobacillus.
For commercial use, specific strains of the L. sanfranciscensis are grown on defined media, freeze-dried, and shipped to bakeries worldwide.