A Review of Withering in the Processing of Black Tea

Abstract

Purpose: Tea is the most frequently consumed drink worldwide, next to water. About 75% of the total world tea production includes black tea, and withering is one of the major processing steps critical for the quality of black tea. There are two types of tea withering methods: physical and chemical withering. Withering can be achieved by using tat, tunnel, drum, and trough withering systems. Of these, the trough withering system is the most commonly used. This study focuses on the different types of withering, their effect on the various quality attributes of tea, and other aspects of withering methods that affect superior quality tea. Results: During physical withering, tea shoots loose moisture content that drops from approximately 70-80% to 60-70% (wet basis). This leads to increased sap concentration in tea leaf cells, and turgid leaves become flaccid. It also prevents tea shoots from damage during maceration or rolling. During chemical withering, complex chemical compounds break down into simpler ones volatile flavor compounds, amino acids, and simple sugars are formed. Withering increases enzymatic activities as well as the concentration of caffeine. Research indicates that about 15% of chlorophyll degradation occurs during withering. It is also reported that during withering lipids break down into simpler compounds and catechin levels decrease. Improper withering can cause adverse effects on subsequent manufacturing operations, such as maceration, rolling, fermentation, drying, and tea storage. Conclusion: Freshly harvested leaves are conditioned physically and chemically for subsequent processing. There is no specified withering duration, but 14-18 h is generally considered the optimum period. Proper and even withering of tea shoots greatly depends on the standards of plucking, handling, transportation, environmental conditions, time, and temperature. Thus, to ensure consumption of high quality tea, the withering step must be monitored carefully.

Effects of Variety, Season, and Region on Theaflavins Content of Fermented Chinese Congou Black Tea

“…Tea is the second most consumed beverage around the world after water. e annual consumption of tea may reach about 2.5 million metric tons (processed leaves), 75% of which is black tea [1]. Congou black tea is a unique variety of Chinese black tea, which is made with careful skill to produce thin, tight strips without breaking the leaves [2].…”

Changes in Phytochemicals and Determination of Optimum Fermentation Time during Black Tea Manufacturing

“…The major changes occurred in the leaf appearance, where the moisture content of leaf reduced from 82.50 to 70.21 %, and reducing sugar reduced from 30 to 20.46 ppm. Changes in carotenoids and organic acids were found due to the breakdown of proteins to amino acids and the breakdown of chlorophyll due to a decrease in moisture content [2]. Besides, withering influences the volatile components and increase caffeine and polyphenol oxidase [2].…”

“…Tea processing consists of a series of stages starting from the harvesting of fresh tea leaves (crop shoots comprising three leaves and a bud (>75 %)) called plucking, through intermediate processing called withering, CTC (Crush, Tear and Curled), fermentation, at last to dry for manufacturing black tea [2][3][4]. Withering reduces the moisture content of tea leaf to make leathery and soft, CTC chops into small and uniform pieces to make granular leaf particles.…”

Applicability of multifunctional preprocessing device for simultaneous estimation of spreading of green tea, withering of black tea and shaking of oolong tea

“…Reasonable pretreatment technologies for fresh tea leaves contribute to increasing the content of tea quality compositions, and improve the characteristic aroma, astringent, strong, bitter and fresh taste of tea brews . In recent years, research on the preprocessing methods of fresh tea leaves has mainly involved the design of tea processing single machinery, the optimization of processing a particular kind of tea, dynamic changes in the major chemical components of tea, changes in tea aroma component contents and impact on tea quality . There have been no reports of a multifunctional preprocessing device synchronously used for spreading of green tea, withering of black tea, and shaking of oolong tea.…”