Kill-green vs oxidation
Every category of tea is decided at one fork: whether heat arrives before the leaf browns, or after. Kill-green and oxidation are the two branches, and the whole six-category structure follows from where a producer puts that heat.
processing method
What is being compared
Point by point
| Aspect | Kill-green (fixation) | Oxidation |
|---|---|---|
| What it does | Denatures polyphenol oxidase, arresting enzymatic oxidation permanently. | Lets polyphenol oxidase act, converting leaf polyphenols into larger coloured compounds. |
| Timing in the process | Early, and once. Everything after it happens to a leaf that has stopped changing colour. | After rupture, and it runs until it is stopped. |
| What stops it | Nothing needs to. It is the stopper. | Heat — which is to say, kill-green. |
| Categories it produces | Green tea, and yellow tea when a further smothering step follows. | Black tea when run to completion; oolong when confined to the bruised leaf margin. |
| Where they meet | In oolong and black tea, applied late to halt oxidation once the maker judges it complete. | In green tea, barely at all, because the heat arrived first. |
| Flavour direction | Preserves fresh, marine and vegetal character; the method adds either umami or toast. | Builds malt, dried fruit, cocoa and the brisk astringency that stands up to milk. |
| The naming problem | Called ‘stopping fermentation’, which is wrong twice over — it stops oxidation, and fermentation means something else in tea. | Called ‘fermentation’ constantly, including by producers, including in direct translation of the Chinese term. |
The short answer
White tea is the interesting case here, because it does neither deliberately: it is withered and dried, with whatever oxidation happens along the way left unmanaged. That is why it sits awkwardly in a scheme built around this fork.
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