Effect of withering/spreading on the physical and chemical properties of tea: A review

Withering and spreading, though slightly differing in their parameters, share the same aim of moisture reduction in tea leaves, and they have a strong impact on the physical and chemical properties of tea. Even though researchers tend to pay close attention to the characteristic crafts of different teas, increasing investigations begin to focus on the withering process due to its profound effects on the composition and content of quality-related compounds. This review provides an overview of tea withering process to address questions comprehensively during withering. Hence, it is expected in this review to figure out factors that affect withering results, the way withering influences the physical and chemical properties of withered leaves and tea quality, and intelligent technologies and devices targeted at withering processes to promote the modernization of the tea industry. Herein, several key withering parameters, including duration, temperature, humidity, light irradiation, airflow, and more, are tailored to different tea types, demanding further exploration of advanced withering devices and real-time monitoring systems. The development of real-time monitoring technology enables objective and real-time adjustment of withering status in order to optimize withering results. Tea quality, including taste, aroma, and color quality, is first shaped during withering due to the change of composition and content of quality-related metabolites through (non)enzymatic reactions, which are easily influenced by the factors above. A thorough understanding of withering is key to improving tea quality effectively and scientifically.