The difference between oxidation and fermentation
The two words are used interchangeably in tea writing and describe entirely different processes. Getting them the wrong way round makes half the category descriptions incoherent.
tea type
What is being compared
Why these get confused
'Fermented' is applied to black tea constantly, including by producers. It is wrong, and the model keeps `oxidationLevel` and `postFermentation` apart because of it.
Point by point
| Aspect | Black tea | Dark tea and pu-erh |
|---|---|---|
| What acts on the leaf | The leaf’s own enzymes, exposed to air when cells are ruptured. | Microorganisms — bacteria and fungi — living on and in the leaf. |
| How long | Hours. | Weeks to decades. |
| Is it alive | No. It is a chemical reaction. | Yes. It depends on a living population. |
| Can it be stopped | Yes, with heat, and that is what fixing does. | Slowed by drying and cold, but raw pu-erh continues for decades. |
| Which teas | Black and oolong. | Dark tea — pu-erh, Fu Zhuan, Liu Bao and their relatives. |
The short answer
Modelling them as separate fields is not pedantry. A tea can be both — aged oolong is oxidised and then ferments — and one field could not express that.
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