Effects of different roasting temperature on flavor and quality of Oolong tea (Tong-Tin Type)

Abstract

The change of liquor color, aroma and taste of oolong tea after roasting have close relation with the change of nonvolatile and volatile compounds. Oolong tea roasted at 8WC still preserved its original golden liquor color, brothy taste, and floral aroma, The high concentrations of linalool, linalool oxides, p-ionone, and 3.7-dimethyl-1.5.7-octatrien-3-01, with a proportional concentration of pyrroles, pyrazines, and furans are probably the main contributors to the pleasant roast aroma of oolong tea roasted at 100°C or 120°C. The high concentrations of pyrroles (1-ethyl-2-formylpyrrole in major), pyrazines (2.5-dimethyl-3-ethyl-pyrazine in major), and furans (5-methyl-2-furfural in major) are probably the main contributors to the over-roast burnt odor of tea roasted at 140°C or above. Obvious deterioration in the quality of tea, such as turning the color of liquor to red and dull, increasing of sour taste and burnt odor of roasted tea, was found when roasted at 140°C or above. Our results strongly suggest that the roasting temperature of high quality oolong tea should not be higher than 80"C, and that of middle-grade tea should be around 100-120^C.