Georgian yeasts and grape cultivars do edit the wine quality in a precision oenology

Georgia, a country of the South Caucasus region, is recognised to be the oldest place with winemaking practice since the Neolithic period. Eight-thousand years of winemaking experience has led to a continuous progress in both the local oenological techniques and the breeding programs of autochthonous grape varieties, consequently becoming the basis for vini-viticuture of this country. Moreover, the home made production of wine is still very popular in rural families and spontaneous fermentation of must is the norm in Georgia. Five Georgian regions, Guria, Imereti, Ratcha-Lechkhumi, Kartli and Kakheti, were chosen for grape and wines sampling; 22 different native cultivars, in 26 vineyards and 19 family cellars were analysed. This study allowed the isolation of one hundred and eighty-two novel wine-associated yeasts from Georgia. Yeast of the collection were ascribed to 15 different species; Metschnikowia pulcherrima (F’ = 0.56, I’ = 0.32), Hanseniaspora guilliermondii (F’ = 0.49, I’ = 0.27), and Cryptococcus flavescens (F’ = 0.31, I’ = 0.11) were the dominant yeasts found on grapes, whereas Saccharomyces cerevisiae showed the highest prevalence into wine samples. Seventy four isolates with fermentative potential were screened for oenological traits such as ethanol production, resistance to SO2, and acetic acid, glycerol and H2S production. Three yeast strains belonging to the Kluyveromyces marxianus, S. cerevisiae and Torulaspora delbrueckii species were selected and separately inoculated in vinifications experiments at a Georgian cellar, using musts from healty grapes of two local cultivars Goruli Mtsvane (B) and Saperavi (N). Physical (°Brix) and microbial analyses (plate counts) were performed to monitor the fermentative process. The results from quantitative GC-FID analysis of volatile compounds revealed that the highest amount of fermentation flavors were significantly more produced in fermentation conducted in Saperavi variety inoculated with K. marxianus, whereas other aromatic compounds showed a higher content in Goruli Mtsvane variety samples fermented by S. cerevisiae. The selected yeast strains have proved to be promising for enhancing the flavor potential in low aromatic Georgian cultivars. This work intends to be a knowledge contribution for a precision oenology toward the strategic concept of “one grape variety-one yeast”.