Microbial Terroir Under Post-Harvest Management: Linking Withering Practices to Grape Microbiome and Metabolome Dynamics in Corvina Grapes

Grape-associated microbial communities are key contributors to wine quality and microbial terroir, yet their dynamics during withering, a critical post-harvest stage for premium sweet and fortified wine production, remain poorly characterized. Using high-throughput metabarcoding (16S rRNA and ITS), we monitored bacterial and fungal communities on Corvina grape berries throughout withering under controlled (C) and non-controlled (NC) dehydration conditions, integrating microbiome data with previously determined volatile organic compound (VOC) and stilbene profiles to uncover taxon–metabolite relationships. Microbial communities underwent progressive restructuring during dehydration. Moreover, the two withering conditions exhibited distinct dehydration kinetics, with C reaching 30% weight loss 14 days earlier than NC, with a significant effect on the abundance of several wine-relevant and spoilage-associated taxa. Metschnikowia was significantly more abundant under C conditions at 10% and 20% weight loss, while Botrytis reached 26.5% relative abundance at 30% weight loss under NC compared with 2.4% under C. A correlation network analysis identified significant associations between Lactobacillus, Acinetobacter, Clostridium, and metabolite accumulation, with Metschnikowia showing positive associations with bioactive compounds and negative associations with spoilage fungi. This first joint time-course analysis of mycobiome and bacteriome dynamics alongside metabolome changes during withering highlights significant associations between microbial succession and grape biochemical changes during withering.