Monitoring and Characterization of the Microbiome of Organic Grapes, Must and Natural Wine During Spontaneous Alcoholic and Malolactic Fermentation

Natural wines represent a new trend in winemaking without use of preservatives and starter cultures, revealing unique quality traits of grapes, wine and terroir, but are susceptible to spoilage or undesirable fermentations. This study aims to highlight the diversity and succession of microbiota of natural wines, from the vineyard (grapes) to mature, fermented wines and the effects of different grape varieties, production stages and equipment. Samples of “Limniona”, “Malagouzia” and “Roditis” grape varieties, initial and fermented must, filtered and unfiltered natural Limniona wines were analyzed in order to enumerate key groups of microorganisms and identify beneficial yeasts and bacteria of alcoholic and malolactic fermentation, respectively, as well as potential marker of off-flavors. Although beneficial fermentation microorganisms (especially Saccharomyces yeasts) were scarce in initial grape, where other contaminants or wild yeasts were present, gradually, as fermentation progresses, there was a prevalence of Saccharomyces cerevisiae strains of increased diversity in matured wine, as well as several lactic acid bacteria (LAB) of malolactic fermentation, mostly Lactobacillus and Oenococcus, and other bacteria from environmental sources, irrelevant to alcoholic/malolactic fermentation or spoilage, like Burkholderia. The type of vessel affected the type of LAB that prevail, with an abundance of Oenococcus in clay vessels, versus Lactobacillus species in stainless steel vessels. Notably, some Lactobacillus species like L. parafarraginis can be linked to off-flavors if they represent a high percentage of the wine microbiota. These findings highlight the importance of understanding, monitoring and controling microbial succession during production stages, in order to prevent sensory faults and ensure stable quality of natural wines.