Effects of pH, Sulfur Dioxide, Storage Time, and Temperature on the Color and Stability of Red Muscadine Grape Wine

Abstract

Red muscadine grape (Vitis rotundifolia Michx.) wines are very susceptible to browning and overall loss of color quality during processing and storage. This study examined the effects of three pH levels (2.90, 3.20, 3.80), three sulfur dioxide levels (25, 50, 75 ppm free SO₂), three storage temperatures (20°C, 30°C, 40°C), and three storage times (0, 3, 9 months). A higher pH resulted in a loss of color intensity and redness and increased browning during storage for nine months. Wine with lower pH had a greater loss of free, unpolymerized anthocyanins, which indicated greater polymerization in lower pH wine. Sulfur dioxide levels higher than 25 ppm free SO₂ severely bleached the color of red muscadine wine and lessened browning in high pH wine only. High SO₂ levels also lessened browning of wine stored at 20°C, but not at higher storage temperatures. Higher storage temperature greatly increased browning and anthocyanin loss during nine months of storage. Wine stored at 30°C or 40°C had unacceptable color after nine months.