Co-evolutionary dynamics of microbial communities and flavor profiles during natural fermentation of Cabernet Sauvignon and Merlot: A comparative study within a single vineyard.

Indigenous microorganisms play a crucial role in determining the quality of naturally fermented wines. However, the impact of grape cultivar specificity on microbial composition is often overshadowed by the geographical location of the vineyard, leading to underestimation of its role in natural wine fermentation. Therefore, this study focuses on different grape cultivars within a single vineyard. The physicochemical results revealed that during fermentation of Merlot and Cabernet Sauvignon wines, ethanol content significantly increased, while residual sugar, pH, malic acid, citric acid, and yeast assimilable nitrogen notably decreased. High-throughput sequencing (HTS) results showed that fungal diversity and richness in Merlot were significantly higher than in Cabernet Sauvignon, whereas bacterial diversity exhibited the opposite trend. The predominant fungal genera in Merlot were Hanseniaspora, followed by Lachancea, whereas the opposite was observed in Cabernet Sauvignon. Erysiphe and Pantoea were exclusively present in Merlot, whereas Erwinia was detected only in Cabernet Sauvignon. A total of 106 flavor compounds were quantified using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS), identifying 22 core volatile compounds in Merlot and 19 in Cabernet Sauvignon. Moreover, at the end of fermentation, the total ester content in Cabernet Sauvignon was significantly higher than in Merlot, imparting a more pronounced fruity and floral aroma, which was further confirmed using sensory analysis. Correlation analysis indicated that Saccharomyces was positively correlated with alcohol content, total acidity, and 16 core volatile compounds, while Hanseniaspora and Lachancea showed opposite correlations. These insights provide a data reference for producing high-quality wines with regional characteristics.