Withering

Definition

Withering (萎凋, weidiao) is the step where freshly plucked leaves are spread out to lose water. Fresh tea leaf is roughly 75 to 80 percent water. As it wilts, the leaf goes limp, which lets it be rolled without snapping, and its chemistry starts to change: cell membranes become more permeable, proteins break down into amino acids, and aroma compounds begin to form. How long and how far the wither runs depends on the tea. Green teas get little or none, just a short spreading to let surface moisture go before kill-green. White tea is defined by its wither: leaves sit for one to three days, indoors or partly in sun, until nearly dry, with slow, light oxidation. Black tea is withered for roughly 12 to 18 hours on troughs with fans blowing air through the leaf, until it has lost a third or more of its weight. Oolong starts with a short sun wither (shaiqing) followed by indoor withering combined with bruising. Weather drives withering. Humid, cool days slow it, and producers adjust with fans, warmed air or longer schedules. A wither that runs too short gives grassy, harsh tea; one that runs too long or too hot gives flat, dull flavor.