Withering

Withering is the first step the maker controls and almost every tea gets one. The leaf is laid out and allowed to lose water, which makes it limp enough to work and starts a set of chemical changes that everything downstream either encourages or cuts short. How long it runs is one of the two or three decisions that settle what type of tea this will be.

What it is

A controlled wilt. The leaf is spread thin, on bamboo racks or tarps outdoors or in indoor troughs with air forced through them and held there while humidity, temperature and airflow are watched. Bed depth matters as much as timing, because a thick layer withers unevenly and an unevenly withered batch cannot be rescued later. The maker calls the end point on weight, on how flaccid the leaf has gone or on smell, and a great many call it by nose alone.

What it does to the leaf

Two things at once and the trade separates them by name. The physical wither takes out moisture, commonly a third to a half of it, and leaves the leaf pliable enough to roll without shattering. The chemical wither is the interesting one. Cell membranes start to break down, chlorophyll degrades, caffeine creeps up, stored carbohydrates are broken down for energy, grassy aromas dissipate and new volatile compounds appear in their place. The same membrane breakdown puts polyphenol oxidase within reach of oxygen, which is why a long wither is already a slow oxidation.

How it's done

The variable is length, not equipment. White tea is withered for 12 to 24 hours and that wither is essentially the whole process. Chinese green gets one to three hours, enough to make the leaf workable before the heat goes on. Chinese black runs five or six hours and can take the leaf to 60 percent moisture loss in that time, well past the third-to-a-half figure quoted for tea in general: published figures are measured on different teas at different points in the wither, so a single number for tea as a whole does not exist. Oolong is withered outdoors on cloths for anywhere from thirty minutes to two hours. Japanese green is the outlier, going straight from the field to the steamer with no controlled wither at all.

What it tastes like

A long wither tastes sweeter, softer and more floral; a short one tastes greener and brighter. It is most of the distance between a Bai Mu Dan, which is essentially a long wither and a dry, and a Long Jing, which is withered only long enough to be workable before it meets the pan. Push it too far and the leaf dries out enough that the enzymes stop working, which strands the tea between styles: no longer fresh, not yet developed.

What people get wrong

Reading withering as drying. Drying happens at the end, with heat, and takes the leaf to a couple of percent moisture so it keeps. Withering happens at ambient or gently warmed temperatures, stops somewhere around half the water gone and exists for the chemical change rather than the preservation. A tea that has been dried has stopped changing. A tea that is withering is doing most of its changing. The second mistake is assuming every tea gets one: Japanese green tea usually goes straight to the steamer with no controlled wither at all and that is part of why it tastes as vividly green as it does.

Where the boundary blurs

Withering and oxidation are not two stages but one process with a change of name. The moment the leaf starts losing water its cell walls begin to fail and enzymatic oxidation starts with them. The line is drawn at the point where the maker begins deliberately damaging the leaf to speed the reaction up. That line is a convention of description. Nothing chemical happens at it, which is why white tea, whose only real operation is a long wither, still comes out lightly oxidised.

Styles where this step is distinctive

and 140 more

teabert, the tealytics teapot, keeper of the kettle

White tea is mostly a long wither and nothing else. That is not laziness, it is the entire technique.

Sources

a controlled wither reduces moisture by about one-third to one-half, degrades chlorophyll, raises caffeine, disperses grassy aromas and breaks down cell walls, initiating polyphenol oxidase and peroxidase activity; withered too long, that enzyme activity ceases through dehydration Gebely, Tea: A User's Guide (2016), ch. 4
withering has two aspects the trade names separately: physical withering, which all teas get and which makes the leaf pliable, and chemical withering, which breaks complex compounds into simpler ones and can start oxidation Uhl, The Art and Craft of Tea (2016), 'Processing'
as water leaves, the leaf collapses on itself and its cell membranes degrade; on exposure to oxygen the fats and proteins inside begin to decompose and free amino acids appear Francl, Steeped: The Chemistry of Tea (2024), ch. 2
withering durations differ by family: 12 to 24 hours for white, one to three hours for Chinese green, five to six hours for Chinese black until the leaf has lost 60 percent of its moisture, and thirty minutes to two hours for wulong; Japanese green usually goes straight to steaming Gascoyne et al., Tea: History, Terroirs, Varieties (2014), 'The Processing of Chinese Teas', 'Processing Japanese Green Teas' and 'Processing Green Wulong Teas'