The effect of pH and ethanol on the astringent sub-qualities of red wine, and the implications for optimum grape maturity /

Abstract

The first objective of this study was to identify appropriate sensory descriptors to assess the astringent sub-qualities of red wine. The influence of pH and ethanol on the sensation of astringency in red wine was evaluated, using a de-alcoholized red wine. A portion of the wine was adjusted to the pH values of 3.2, 3.4, 3.6 and 3.8, and another portion was adjusted to ethanol concentrations of 0%, 6%, 12%, and 15%. In addition, the pH 3.4 and 3.6 treatments were adjusted to an ethanol concentration of 12% and 15% all wines were then assessed sensorially and seventeen terms were identified, through panel discussion, to describe the mouth-feel and taste qualities: velvet, aggressive, silk/satin, dry, fleshy, unripe, pucker viscosity, abrasive, heat, chewy, acidity, grippy/adhesive, bitter, balance, overall astringency, and mouth-coat. Descriptive analysis profiling techniques were used to train the panel and measure the intensity of these attributes. It was found that decreasing pH values (averaged across all ethanol concentrations) showed an increase in the overall astringency of the wine. The combined treatments of ethanol and pH, real wine parameters (pH 3.4 and 3.6; 12% and 15% ethanol) did not have an effect on the perception of the astringent sub-qualities of the wine. A time intensity study was also included using the pH and ethanol adjusted wines, which showed that as the ethanol level of the wines increased so did the time to maximum intensity. The second objective was to identify appropriate sensory descriptors to evaluate the influence of grape maturity and maceration technique (grape skin contact) on the astringency sub-qualities of red vinifera wines from Niagara. The grapes were harvested across two dates, representing an early harvest and a late harvest. A portion of the Cabernet Sauvignon grapes wine was divided into three maceration treatments of oneweek maceration, standard two-week maceration, three-week maceration, and MCM. Another portion of both the early and late harvest Cabernet Sauvignon grapes were chaptalized to yield a final ethanol concentration of 14.5%. The wines were assessed sensorially and thirteen terms were identified, through panel discussion, to describe the mouth-feel and taste qualities: carbon dioxide, pucker, acidity, silk/chamois, dusty/chalky/powdery, sandpaper, numbing, grippy/adhesive, dry, mouthcoat, bitter, balance and, overall astringency. Descriptive analysis techniques were used to train the panel and measure the intensity of these attributes. The data revealed few significant differences in the mouth-feel of the wines with respect to maturity; which included differences in overall astringency and balance. There were varietal differences between Cabernet Sauvignon, Cabernet Franc, and Pinot Noir and differences for Cabernet Sauvignon wines due to the length and manner of maceration and as a result of chaptalization. Statistical analysis revealed a more complex mouth-feel for the Pinot Noir wines; and an increase in the intensity of the astringent sub-qualities as a result of the addition of sugar to the wines. These findings have implications for how processing decisions, such as optimum grape maturity and vinification methods may affect red wine quality.