The Science Within: Understanding the Symbiotic Partnership of Yeast and Bacteria

The sourdough ecosystem is built upon a symbiotic partnership between two primary groups of microorganisms: wild yeasts and Lactic Acid Bacteria (LAB). The dominant yeasts often include species such as Saccharomyces cerevisiae and Kazachstania humilis, while the bacteria are primarily from the Lactobacillus genus. This relationship is mutually beneficial; LAB can metabolize certain sugars within the flour that yeasts cannot, and in turn, yeasts consume some of the metabolic byproducts of the LAB fermentation process. This codependency creates a remarkably stable and resilient culture capable of outcompeting spoilage microbes. A key characteristic of a mature starter is the population balance: it typically contains as many as 100 times more bacterial cells than yeast cells, a ratio that highlights the profound influence of bacteria on the final bread's flavor, texture, and keeping qualities.