Color and Color Stability of Red Wine from Noble (Vitis rotundifolia Michx.) and Cabernet Sauvignon (Vitis vinifera L.) at Various pH

Muscadine grapes (Vitis rotundifolia) are the most widely planted grapes in the south and southeast United States due to their suitability in these areas. Most of the commercial muscadine grape crop is used to produce wine. Wine made from suitable cultivars of muscadine grapes possesses a very fruity, unique flavor and aroma that appeals to many people in the South. However, muscadine grape products are very susceptible to browning and overall loss of color quality during processing and storage (1,4,7). This color instability is severely limiting the marketability of red muscadine wines. Several factors have been shown to influence the color quality and stability of red muscadine wines. The anthocyanin content and composition and conditions of processing and storage have been shown to have a major affect on the color and stability of red muscadine products (1,2,4,7). Muscadine grapes contain only the 3,5-diglucosi de anthocyanins (1), which have been reported to be more susceptible to browning than are the monoglucoside anthocyanins (6). This might indicate why red muscadine wines tend to brown. Monoglucoside anthocyanins are the predominant pigments in Vitis vinifera wines (8), and red vinifera wines are generally considered to have relat1vely stable color. The effects of pH on the color of red Vitis vinifera wines has been well documented (10,11,12). These effects of pH have also been observed in red muscadine wine (7), with a higher pH causing the wine to be less red and less intense. In the same research (7), red muscadine wine with a higher pH also browned to a much greater extent than did wine with a lower pH. Lower pH wine also had a greater loss of pH responsive anthocyanin than higher pH wine, which indicated greater polymerization of anthocyanin at lower pH. The formation of various anthocyanin-tannin complexes or polymers during aging of red wines has been well documented (3,5,9), and it has also been shown that these anthocyanin-tannin complexes help stabilize the wine color (8). Perhaps the color instability of red muscadine wine is due to greater polymerization of anthocyanins and tannins. Further research is needed to compare the color components and anthocyanin-tannin polymerization of red muscadine wine with that of a red vinifera wine with relatively stable color such as Cabernet Sauvignon at various pH.