As many San Franciscans have noticed, sourdough bread stays fresher longer than the regular stuff. Sourdough’s extended freshness is due to extra fermentation that traps more moisture in the dough. But now we know that sourdough’s longevity is also because it can ward off mold. Because bacteria in some sourdough starters actually produce mold-killing compounds—essentially natural preservatives.

Most sourdough starters contain strains of Lactobacillus bacteria, like the poster child Lactobacillus sanfranciscensis. Eight years ago, researchers isolated another strain called Lactobacillus hammesii from a French sourdough starter.

They've now discovered that the strain pumps out a potent antifungal as it digests bread flour. So they baked bread with the L. hammesii starter, sliced it, and waited. The loaf resisted mold for 12 days—a few days more than L. sanfranciscensis sourdough, and twice as long as typical bread. Those results are in the journal Applied and Environmental Microbiology. [Brenna A. Black et al., Antifungal hydroxy-fatty acids produced during sourdough fermentation: microbial and enzymatic pathways, and antifungal activity in bread]

L. hammesii isn't the most common sourdough strain. But researchers say it could eliminate the need for added preservatives. Which would mean store-bought sourdough that's additive-free and lasts for weeks. Assuming you can wait that long to eat it.

—Christopher Intagliata

[The above text is a transcript of this podcast.]