Kill-Green (Shaqing)
Kill-green, or shaqing, is the heating step that destroys a tea leaf's oxidizing enzymes, locking in green color; it is done by pan-firing, steaming or baking.
Definition
Kill-green (杀青, shaqing, literally "kill the green") is the step that stops oxidation. Fresh leaf is heated quickly enough to denature the enzymes, mainly polyphenol oxidase, that would otherwise turn it brown. In English the step is also called fixing, de-enzyming or firing. It is the defining step of green tea and also appears in yellow tea, oolong and the leaf used for pu'er. The heat source shapes the flavor. Most Chinese green teas are pan-fired (chaoqing) in a hot wok or a rotating drum, which gives nutty, toasty, chestnut-like notes. Japanese teas are almost all steamed (zhengqing), which gives a brighter green leaf and vegetal, marine, sometimes spinach-like flavor. A few teas are fixed by baking or hot air. Timing within the process defines the tea class. Green tea is fixed soon after plucking, with little withering. Oolong is fixed only after withering and bruising have taken oxidation as far as the maker wants. Pu'er maocha is pan-fired at a lower intensity, which is thought to leave some enzyme activity and help the leaf change during aging. White tea and black tea have no kill-green step at all.
In Depth
Why it is hard: the leaf has to heat through fast and evenly. Too little heat leaves live enzymes, and the tea turns reddish with a sour, stewed taste. Too much heat scorches edges, giving burnt spots and a smoky, bitter note. Skilled hand firers judge it by touch, sound and smell, and large producers use drum fixers with controlled temperature and dwell time.
Spotting it in the cup: pan-fired green tea tends to have a yellow-green liquor with roasted nut and bean aromas. Steamed green tea brews greener and cloudier, with grassy and seaweed notes. If a green tea shows browning or a stewed fruit smell, the kill-green was likely incomplete.
Common confusion: kill-green is not the same as drying. The leaf leaves the fixing stage soft and still moist; it is rolled and dried afterward.
See Also
- Green Tea Processing
- Tea Processing