FIG 1.

Isolation of yeast from clay vessels. (A) Yeast strains in clay vessels. Scanning electron microscope (SEM) pictures of the inside of a modern clay vessel buried in the ground for 3 weeks without beer (left panel) and presoaked with unfiltered beer (middle panel) prior to burial. On the right panel is a 2-year out-of-use wine clay vessel (bottom) that yielded live yeast cells, observed as colonies and by electron microscopy (EM [upper panel]). Yeast cells were only successfully isolated from the last two vessels. (B) The pipeline of yeast isolation and characterization from vessels. Putative fermented beverage-containing vessels were carefully dismantled. Small pieces were sent for scanning electron microscopy (SEM), and the rest were incubated in growth medium (YPD) for 72 h at room temperature. Samples were plated on selective plates with antibiotics to eliminate bacteria. After 72 h, yeast colonies appeared and were regrown on new plates. The yeast strains were taken for various analyses, including full-genome sequencing and comparison of growth under fermentation-related conditions in beer wort. In addition, beer was brewed according to a standard recipe using the isolated yeast strains. The presence of aromatic and flavor compounds in the beers was analyzed quantitatively, and their flavor was qualitatively evaluated by specialized beer tasters.