Yellowing
Yellowing is the step that makes yellow tea yellow and it is the rarest operation in tea. After the kill-green, the still-warm leaf is smothered under a damp cloth and left to change slowly in its own heat. Its enzymes are already dead by then, so what happens is not the enzymatic oxidation that makes an oolong. It is a slower, non-enzymatic change that takes the edge off a green tea.
What it is
A deliberate smother, sometimes called sweltering. The leaf is fixed as though it were going to be green tea, then, while still warm and still holding moisture, it is either gathered and tied in cloth or paper and kept in a covered container, or spread directly on the ground and covered over. Either way it is held warm and humid and left alone. Published durations run from four hours to several days, and the leaf is wrapped in some places and laid out in others, which is a fair reflection of a technique that survives in a handful of places and is not standardised across them.
What it does to the leaf
Non-enzymatic oxidation in warm damp. Catechins convert into compounds that are less astringent, chlorophyll degrades and takes both the leaf and the liquor toward yellow, and proteins break down into free amino acids, which read as sweetness. The tea comes out measurably less bitter than the green tea it started as, with its floral side pushed forward. In some places the leaf is then dried, wrapped and rested a second time before its final shaping and drying, so the smother can happen more than once.
How it's done
One method with variations in the wrapping and the number of rounds. In one, the leaf is spread on the ground under a damp cloth for four to ten hours, with the length adjusted to the weather. In the other it is tied in cloth or paper, placed in a container, covered and kept warm for several days, then dried, wrapped and aged a second time before it is shaped and dried for good. The pluck on the way in is unusually strict: for a high-grade yellow, only the bud, taken before it turns downy.
What it tastes like
Like a green tea with the sharpness sanded off. Sweeter, mellower and rounder, noticeably less bitter than the same leaf would be as green tea, with the floral note more obvious for the loss of the grassy one. The liquor carries the yellow tint the name refers to, which comes from the chlorophyll breaking down rather than from any browning of the polyphenols.
What people get wrong
Calling this a light oxidation like a white tea's. The mechanism is different. A white tea's slow change is enzymatic, driven by the leaf's own polyphenol oxidase across a long wither, while yellowing happens after those enzymes have been killed and cannot be doing anything at all. The second mistake is expecting yellow tea to be easy to find. It came close to dying out, a few names such as Jun Shan Yin Zhen survive and one province still makes it in any quantity.
Styles where this step is distinctive
Sources
- yellow tea is heated to destroy the oxidative enzymes and then sweltered: gathered, tied in cloth or paper, placed in a container, covered with a damp cloth and kept warm for several days, during which non-enzymatic oxidation occurs Francl, Steeped: The Chemistry of Tea (2024), ch. 2
- the sweltering makes yellow tea sweeter and mellower than green tea by oxidising catechins to less astringent compounds, degrades the chlorophyll to give the yellow colour and breaks proteins into free amino acids that add sweetness Francl, Steeped: The Chemistry of Tea (2024), ch. 2
- in Chinese production the still-warm leaves are spread on the ground and left covered with a damp cloth for four to ten hours depending on the weather; only the bud is picked, before it becomes downy Gascoyne et al., Tea: History, Terroirs, Varieties (2014), 'The Processing of Chinese Teas'
- yellow teas are increasingly rare, with only a few such as Jun Shan Yin Zhen remaining and one province still producing limited quantities Gascoyne et al., Tea: History, Terroirs, Varieties (2014), 'The Processing of Chinese Teas'