Georgian Viticulture and Winemaking: From Modernity to Past Biodiversity survey and selection of Georgian wine yeasts

The work focused on investigating the biodiversity of yeast strains in five different regions in Georgia (Guria, Imereti, Kakheti, Kartli, and Ratcha-Lechkhumi) by collecting samples of grapes and wines in 26 vineyards and 19 family cellars which used spontaneous fermentation style. A total of 182 yeast strains were isolated and identified into 15 different species using molecular techniques (PCR-ITS and RFLP, and partial sequencing of the 26S rDNA gene). Results highlighted that the dominant species found on grapes were Metschnikowia pulcherrima, Hanseniaspora guilliermondii and Cryptococcus flavescens. In contrast, Saccharomyces cerevisiae was the most prevalent yeast species in wine samples. 74 yeast isolates with the potential for wine fermentation were screened for various oenological traits, including ethanol production, resistance to sulphur dioxide (SO2), and the production of acetic acid, glycerol, and hydrogen sulfide (H2S). Three yeast strains were selected for further micro-vinification experiments (Kluyveromyces marxianus UMY207, Saccharomyces cerevisiae UMY255, and Torulaspora delbrueckii UMY196) inoculated in musts of local Georgian grape varieties, Goruli Mtsvane and Saperavi. The study found that significant interactions were present between yeast strain and grape variety factors on the flavour profile of the final products. Particularly, K. marxianus led to the production of specific aromatic compounds in Goruli Mtsvane wines, while S. cerevisiae enhanced the volatiles in Saperavi ones. The study aligns with the concept of matching specific yeast strains with particular grape varieties to optimize the flavour profile of wines, emphasizing the importance of yeast selection in winemaking.