Taylor Cowan • July 14, 2022

Withering, Wondering, Watching: A Quick Dive into Tea Withering

black teaeducationgreen teahualien teawhite tea

Mr. Zhou with his Sanxia Bilouchun, Formosa Green Snail

Mr. Zhou with his Sanxia Biluochun, Formosa Green Snail.

Withering may seem boring

it's like watching paint dry, only with leaves—but it's one of the most crucial steps in tea production.

The tea leaf begins wilting the moment it is plucked. Withering is the controlled dehydration and concentration of aromatic compounds. This can occur outdoors or indoors, though UV sunlights assists in the process.

Withering can happen in a variety of contexts: bamboo baskets, troughs, air dryers, and tarps strewn out in the sun.
 

Withering also creates suppleness and pliability in the leaf for the next steps. Withering can happen in a variety of contexts: bamboo baskets, troughs, air dryers, and tarps strewn out in the sun.

 
During solar withering, the blue light of the sun causes a tea leaf open its stomatal pores, letting water evaporate. The leaf is parched. It desperately tries to close the pores but can’t because of the sunlight. So it releases an emergency sealant—abscisic acid which seals the pores.
Bamboo tumblers, like pictured here, assist in withering. 
Why tell all this? Because abscisic acid is rife with floral organic compounds, which you’ll taste in the finished cup.
 
Once the vacuole (aka “break-in-case-of-emergency-water") of a planet cell is totally drained, it creates space for the intermingling and degradation of carbohydrates and sugars in what will eventually create a tea’s aroma complex.
When cell walls break down, polyphenol oxidase enters—the agent of oxidation.
Note the difference between the fresh picked and perky tea leaves vs. their withered counterpart.
But, without rolling or further encouraging oxidation, the result will be a mottled, inconsistent and mixed oxidative spectrum—not quite the vivid red “complex” polyphenols of a black tea.
Withering can take all day (or days!) in some cases, depending on the climate conditions. Experienced producers use simply their touch, sight and smell to determine when a batch of picked tea leaves is sufficiently withered.
Mr. Chui monitors his withering Li Shan by smell.