Effects of different withering temperatures and times on the quality of summer white tea

【Objective】 In order to explore the effect of withering temperature and time on the quality of summer white tea, clarify the key time point of white tea quality transformation, and provide reference for the comprehensive utilization of summer and autumn tea resources, white tea production and processing and quality improvement.【Method】 With one bud and one leaf of Fuding Dabai tea as test material, the effects of different withering temperatures(18, 23 and 28℃) and different withering times(0, 8, 16, 24, 32, 40 and 48 h) on the color of white tea products and the sensory quality, biochemical components and taste attributes of finished tea were studied by high performance liquid chromatography, Lab color model, electronic tongue and sensory evaluation under the condition of humidity control(65±5)%. The optimum withering temperature and time of summer white tea were comprehensively evaluated by systematic cluster analysis and principal component analysis.【Result】 The results showed that with the prolongation of withering time, the water content, color saturation and hue chroma of white tea in process gradually decreased, and the color became darker and yellower. The color change range under different temperature withering was 23℃>28℃>18℃. The sensory evaluation score of the tea increased first and then decreased. The optimum withering time at 18, 23 and 28℃ was 40, 32 and 32 h, respectively. The optimum withering temperature of summer white tea was 23℃, which was conducive to the formation of flower aroma. The contents of tea polyphenols, catechin, epigallocatechin gallate and epicatechin gallate decreased, the contents of amino acids and epicatechin increased first and then decreased, the contents of caffeine, gallic acid and gallocatechin increased, the salty and sour tastes of tea soup decreased first and then increased. The results of cluster analysis showed that the quality of withering white tea at low temperature(18℃) was significantly different from that of other white teas at two different withering temperatures, and its quality transformation was the slowest. The transformation began at 16 h of withering, and the difference was obvious at 40 h of withering. The difference was significant at 23℃ withering to 24 h and 28℃ withering to 32 h. The results of principal component analysis showed that the cumulative contribution rate of the first five principal components was 87.63%. The first principal component mainly integrated the information of color, shape and bitter and astringent substances. The total score of sensory evaluation, leaf base score, aroma score, astringent and salty taste had a greater contribution to the second principal component. The fourth principal component mainly integrated the information of sweet substances.【Conclusion】 Under the condition of humidity control(65±5)%, the key nodes of quality transformation, the optimum withering temperature(23℃) and the optimum withering time(18℃ 40 h, 23℃ 32 h, 28℃ 32 h) are determined by combining the color of summer white tea products and the sensory quality, biochemical components and taste properties of finished tea. The results of this study can be used to regulate the quality and flavor of summer white tea.