Fermentation-Based Valorization of Grapevine Waste: Microbial Bioconversion, Bioactive Recovery, and Industrial Bioprocess Integration

Vineyard management and winemaking leave behind large residue streams that are still rarely used as fermentation feedstocks. This review considers how pomace, skins, seeds, stems, canes, pruning wood, leaves and wine lees can be directed toward microbial bioconversion, fermentation-assisted recovery of bioactive compounds, and circular biorefinery schemes. Their composition (phenolics, stilbenes, dietary fiber, lignocellulose, sugars, minerals and yeast-derived material) makes them workable in either solid-state or submerged fermentation. We describe the routes that lead to enzymes, organic acids, ethanol, microbial biomass, biosurfactants, pigments and functional ingredients, together with the mechanisms by which bound phenolics are released and transformed. Green extraction, downstream purification, analytical standardization and process intensification are treated next, since market-ready consistency depends on them. The remaining obstacles are then set out: feedstock variability, phenolic inhibition, strain safety, scale-up, product stability, regulatory demands and economics. The data show grapevine waste as a versatile and valuable fermentation substrate and identify the reasons why laboratory results have not yet reached industrial scale.