Effects of Caffeic Acid Concentration on Copigmentation and Color Quality of Blueberry Wines with Different Residual-Sugar Levels

Color stability is a critical quality attribute of blueberry wine, yet anthocyanin degradation and insufficient copigmentation during processing and storage can lead to undesirable color changes and reduced sensory quality. This study investigated the effects of caffeic acid on copigmentation and color quality in dry, semi-dry, semi-sweet, and sweet blueberry wines. Wines were treated with different caffeic acid concentrations and evaluated for physicochemical properties, color characteristics, phenolic compounds, anthocyanin-related indices, and electronic-tongue responses. Caffeic acid caused no substantial changes in pH, total sugar, total acidity, or alcohol content. At appropriate concentrations, it decreased lightness, increased redness and blue-purple hue, and enhanced color density, bathochromic shift, and copigmentation. It also resulted in higher measured total phenolic, flavonoid, and anthocyanin contents and increased WCP, WC, CDR SO2, and CA, providing spectrophotometric evidence consistent with enhanced anthocyanin color expression and copigmentation-related interactions. Effects varied with residual-sugar level: the strongest overall effects occurred at 300 mg/L in dry wine and 400 mg/L in semi-dry, semi-sweet, and sweet wines. Electronic-tongue analysis showed increased sensor responses corresponding to aftertaste and richness and a decreased bitterness-related sensor response. Overall, caffeic acid was associated with enhanced immediate color expression and spectrophotometric responses consistent with copigmentation, with the magnitude of these responses depending on caffeic acid concentration and residual-sugar category. These findings provide a theoretical basis and practical guidance for the targeted use of caffeic acid as a copigmentation enhancer for color management in blueberry wines with different residual-sugar levels.