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What happens to tea leaves during the withering stage of black tea processing?

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Neatly planted rows of green tea bushes stretch across rolling fields with Mount Fuji, capped with snow, rising in the background in Japan. — tea Rows of tea (*Camellia sinensis*) growing in Japan, with Mount Fuji in the background.

During the withering stage of black tea processing, the leaves undergo both physical and chemical changes to prepare them for further manufacturing.12

Physical Changes

The primary physical change is the loss of moisture. Freshly plucked leaves typically have a moisture content of 70 to 80 percent by weight. Through the withering process, this is reduced to 55 to 70 percent, causing the leaves to become flaccid. This process can be performed using traditional methods, such as spreading leaves on trays, or through various mechanized systems like trough, drum, or tunnel withering, which use forced or hot air to accelerate the process.1

Chemical Changes

Beyond moisture loss, the leaves undergo chemical withering, which is essential for developing the final quality of the tea. During this phase:12
* Proteins and carbohydrates break down into simpler amino acids and sugars.1
* The concentration of caffeine and polyphenols increases.1

While mechanized systems significantly reduce the time required for withering, they may potentially lower the quality of the final product if they do not allow sufficient time for these critical chemical reactions to occur.1