High-sugar driven microbial dynamics in spontaneous fermentations of Lebanese cooked wines.

Traditional Lebanese cooked wines are produced by boiling grapes to concentrate the must, creating an extreme environment marked by high sugar levels where fermentation occurs spontaneously. This study investigated the microbial dynamics and chemical changes occurring in seven fermentations of cooked must from four wineries. Using high-throughput amplicon sequencing of bacterial 16S and fungal ITS2 regions, combined with culture-dependent for yeast isolation and HPLC analyses, we monitored microbial and chemical changes from fresh juice and along the fermentation. Sugar concentrations increased to as high as 725 gL-1 after boiling, while the pH remained stable (3.26-3.90). Fermentation kinetics varied according to the initial sugar concentration, with lag time ranging from 2 to 6 days in fermentations starting below 350 g L-1 to 14-24 days for those exceeding this threshold. Despite prolonged fermentations, ethanol yields remained relatively low (48-129 g L-1). Sugar concentration significantly influenced microbial composition (PERMANOVA, p < 0.0001) despite variability in composition between vats and fermentation processes. A resilient core microbiota dominated by Starmerella bacillaris, Hanseniaspora spp., Saccharomyces cerevisiae, and Fructilactobacillus sanfranciscensis was consistently detected in all vats along the fermentation. Unlike with conventional non-concentrated grape wines, where S. cerevisiae dominates and Oenococcus oeni drives malolactic fermentation, cooked wines showed the persistence of osmotolerant yeasts and the dominance of F. sanfranciscensis. Correlation analyses linked S. bacillaris to glycerol, malate, and citrate, suggesting its role in osmoadaptation and sensory modulation. Our findings provide new insights into microbial resilience and succession under extreme wine fermentation conditions and contribute to the valorization of artisanal winemaking practices.