Wild microbial communities shaping the spontaneous fermentation of biodynamic Malbec wine

Prior to the industrialisation of winemaking, spontaneous fermentation was the only option available to wineries, relying exclusively on native micro-organisms from the vineyard due to the absence of commercial inoculants. While nowadays inoculation is a practical choice for industrial-scale producers, small wineries aiming to craft distinctive wines can benefit from the complexity and uniqueness of spontaneous fermentation. However, the unpredictable interactions among the diverse community of bacteria and fungi during fermentation pose significant challenges. Understanding these microbial interactions is essential for making informed winemaking decisions. In this study, we analysed the microbiome, physicochemical, and sensorial profiles of Malbec wines produced from biodynamic vineyard plots subjected to different management practices, including organic amendment incorporation and hail net placement, over three seasons. Our results revealed significant heterogeneity between individual fermentations, with no clear effects of vineyard treatments on the final wine profiles. Notably, metabarcoding analysis revealed a remarkable persistence of DNA signatures from the native fungal consortium; specifically, Hanseniaspora nectarophila and Hanseniaspora guilliermondii remained detectable until 75 % of alcoholic fermentation (AF). Along with Saccharomyces cerevisiae, Schizosaccharomyces japonicus, and Metschnikowia pulcherrima, these taxonomic signals were consistent throughout the vintages, though the latter two were more sensitive to seasonal climate variations. These findings underscore the critical role of locally adapted consortia in shaping the unique expression of wines.