环境温湿度调控对茶鲜叶萎凋失水及白茶品质的影响

Effect of Temperature and RH during Withering on Water Loss and Quality of White Tea

为改进白茶萎凋工艺,并为实现白茶加工品质的稳定性和可控性提供依据。以福鼎大毫茶1芽1～2叶鲜叶为原料,研究不同温度、湿度环境对茶鲜叶萎凋失水速度和白茶品质特征及生化成分的影响。结果表明,茶鲜叶在萎凋过程中失水速度呈先快后慢的趋势,存在2个明显的失水速度变化临界点,在萎凋减重率达40%前失水速度较快,40%～70%失水速度明显减慢,70%后失水很慢。在相同温度(25、30或35℃)条件下,随环境湿度的增加,萎凋叶失水速度减慢;在相同湿度(RH 65%、75%或85%)条件下,随环境温度的降低,在萎凋初期(减重率≤30%)失水速度加快,后期失水速度减慢。萎凋温度、湿度条件能有效调控茶鲜叶萎凋失水速度,进而影响白茶生化成分与感官品质。在高温低湿(35℃、RH65%)条件下萎凋叶失水速度过快,儿茶素含量较高,氨基酸含量较低,成茶白茶品质特征较不明显;在高温高湿(35℃、RH85%)条件下萎凋失水过慢,儿茶素类明显降低,氨基酸、咖啡碱含量增加,成茶易产生"发酵香",降低品质。由此可见,选择中、高温中湿(30～35℃、RH 75%)或中低温(25～30℃)环境调控茶鲜叶萎凋失水速度,可获得品质相对较好的白茶。

This study aimed to improve the withering process in white tea manufacturing in order to enhance the stability, quality and flavor of the tea. The shoots of a bud and one or two leaves from Fuding Dahao tea plant （Camellia sinensis） were used for the experimentation. The effects of temperature and RH during withering of the white tea on the dehydration rate, sensory quality and chemical composition of the tea were investigated. The leaf dehydration was rapid in the beginning of the withering until the weight loss reached 40%0. Then, it slowed significantly till the weight loss became 70%, when the dehydration rate leveled off. At a same temperature （25℃, 30℃ or 35℃）, the higher RH in the withering chamber, the slower the weight loss rate became. But during the prophase of the withering process （i. e. , weight loss at less than 30%）, low temperatures accelerated the water loss at constant RH （65%, 75% or 85%）. The leaf dehydration rate significantly affected the quality, flavor and chemical constituents of the white tea. Higher dehydration rate at high temperatures and low humidity （e. g. , 35℃ and 65% RH） resulted in higher catechin and lower amino acids content in the tea product. The tea flavor was not as significantly affected, though. At 35℃ and 85% RH, the dehydration slowed down significantly with much decreased catechin and amino acids, but increased caffeine content. At the same time, the ＂fermented odor＂ that can ill-affect the delicate tea flavor was generated. Thus, it was concluded that the desirable quality and flavor could be obtained by controlling the dehydration rate of tea leaves during withering process with a moderate RH of 75% at 30 --35℃ or 25--30℃.