A seep from the past: Isolation and characterization of live yeast cells from ancient beer vessels and analysis of the bevrages they produce

Ancient microorganisms have been primarily studied using ancient-DNA techniques. Additionally, reconstructions of ancient fermented beverages relied on ancient recipes or chemical residues, using modern yeast. Here, we hypothesize that highly enriched yeast populations that were present in fermented beverages would have become the dominant microorganism species in the vessel, and the descendants of these yeast could be directly isolated from the vessels and studied. Initially, we developed an isolation pipeline of yeast from modern clay vessels. Using this protocol, we screened for yeast presence in beverage related and non-related ancient vessels and sediments from several sites in Israel. We found that yeast cells were successfully isolated from clay containers of fermented beverages, in a significantly higher proportion than from non-beverage-related ones. Furthermore, genomic analysis of the isolated yeast revealed that they are similar to strains found in traditional African beer and mead, supporting the notion that they originated from fermenting yeast. Lastly, the yeast strains isolated from the putative beverage containers grew in wort and produced a beer which is similar to modern beer, while the few yeast strains isolated from non-related vessels and sediments, did not produce drinkable beer. Our data suggest that the yeast cells we isolated from the beverage containers are descendants of the original yeast that fermented the ancient beverage. These findings enable to more accurately define ancient beverages, and open a new avenue in experimental archeology: research of the ancient microorganism content of fermented beverages and food.