Researchers at North Carolina State University have found that while a specific yeast dominates sourdough starters regardless of flour type, bacterial communities vary based on the flour used, potentially affecting bread's flavor and texture. The study, published in Microbiology Spectrum, highlights how environmental factors like flour influence these microbes. This work began as a classroom experiment to teach students about fermentation and evolution.
Sourdough starters, a mix of flour and water that ferments to leaven bread, host diverse microorganisms responsible for the bread's tangy taste and chewy texture. A new study reveals that these microbes do not emerge randomly but are influenced by the flour bakers choose.
Led by evolutionary biologist Caiti Heil, Ph.D., at North Carolina State University in Raleigh, the research examined how different flours affect starter microbiomes. The team analyzed starters fed with all-purpose flour, bread flour, or whole wheat flour over several weeks using metabarcoding, a technique that identifies microbes genetically.
Results showed that yeasts from the genus Kazachstania consistently dominated all starters, regardless of flour type or feeding schedule. This was unexpected, as the researchers anticipated Saccharomyces cerevisiae, the common brewer's yeast. In contrast, bacterial profiles differed: whole wheat flour starters had higher levels of Companilactobacillus, while bread flour ones featured more Levilactobacillus.
"We can use sourdough as an experimental evolution framework, to see what happens over time," Heil explained. She added, "And because the microbial composition affects different traits, by altering the flour you could potentially alter how your bread tastes."
The project originated from an educational initiative by postdoctoral researcher Enrique Schwarzkopf, Ph.D., who runs a middle school program on fermentation. Students tested various flour combinations to observe microbial growth in starters like Schwarzkopf's own, named Seth.
Previous studies have identified over 60 bacteria species and 80 yeast types in global sourdoughs, shaped by factors including flour nutrients, air, surfaces, and even bakers' hands. Grains like wheat, rye, barley, teff, and millet provide distinct nutrients that microbes rely on.
Heil's work underscores flour as an ecological driver, offering insights into how microbial communities form, compete, and adapt in changing environments. The findings appear in Microbiology Spectrum (2026; 14(1)), with authors including Sima Taheri, Enrique Schwarzkopf, and others.
