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

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%.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℃.