The effect of stem contact fermentation on the quality of Cabernet Sauvignon and Merlot wines from Yantai, China

Grapes grown in the Yantai wine region typically exhibit lower phenolic content and sugar levels, resulting in wines with relatively lower sensory quality. This study aims to assess the impact of stem-contact fermentation on the quality of wines from this region. Cabernet Sauvignon and Merlot grapes were selected winemaking, using three approaches: 100% destemming, and stem-contact fermentation with 10% and 20% grape stems, respectively. After alcoholic fermentation, the wines were analyzed for oenological parameters, phenolic compounds, color parameters, volatile compounds, and sensory evaluation. The results showed that stems did not negatively impact the oenological parameters. In Cabernet Sauvignon wines, stems resulted in a significant increase in total phenolics, anthocyanins, and tannins. In Merlot wines, stems caused a significant increase in total phenolics and a notable reduction in total anthocyanins. Stems primarily affected the anthocyanin content in both Cabernet Sauvignon and Merlot wines, with minimal effects on the proportions of individual anthocyanins. PLS-DA analysis further revealed that stems significantly affected the levels of total tannins, (-)-epigallocatechin, and total phenolic compounds in Cabernet Sauvignon wines, as well as the levels of (-)-epigallocatechin and total phenolics in Merlot wines. The presence of grape stems also significantly influenced the volatile compounds in the wine. When 20% of grapes retained their stems, there was a trend toward higher volatile content, resulting a more complex aroma profile. Overall, retaining some stems during fermentation is an effective strategy to enhance the quality of wines from the Yantai wine region.