Bitterness
A taste, detected on the tongue, and the most frequently misfiled word in tea writing.
Bitterness in tea comes mainly from caffeine and from the catechins, and it rises with water temperature, with steep time and with leaf-to-water ratio. It is a taste in the strict sense: it is registered on the tongue, and the sensation stops when the liquid leaves the mouth. That is what separates it from astringency, which continues after swallowing because it is a physical change in the mouth rather than a flavour arriving. Chinese tasting vocabulary keeps the two apart as ku (bitter) and se (astringent, puckering) and regards a tea that is ku without being se as a different and often better thing than one that is both. English-language tea writing usually has one word for both sensations, which is why so much brewing advice pairs a correct diagnosis with the wrong fix.
Which sense this is
Taste. Registered on the tongue. There are few of these and tea writing uses them loosely — most words that sound like tastes are smells.
Taste, not mouthfeel. TeaHQ's own vocabulary file currently disagrees: `mouthfeelSchema` in `src/domain/vocabularies.ts` lists `bitter` among texture terms, and eleven teas carry it there. That is the error this axis field exists to make visible, and it is recorded rather than quietly patched.
Sensory primitive. A single sensation that can be isolated and trained on, independently of what the tea reminds anyone of.
Where it comes from
- Brewing variable
Hotter water and longer contact extract more caffeine and more catechins, so bitterness rises with both. This is the first thing to change when a cup is harsher than expected.
Produced at the drinker's end, by a brewing choice or a brewing error.
- Established chemistry
Caffeine is bitter, and the catechin group contributes bitterness alongside astringency. The contribution is shared across a family of related compounds rather than traceable to one molecule.
The chemical route is identified in the literature. Often a family of related compounds rather than one named molecule.
- Processing step
Shading before plucking is associated with lower bitterness in the resulting tea, which is one reason gyokuro and tencha are grown under cover.
A named production step reliably produces it. A statement about practice, not about chemistry.
Processing: process-shading. Types: type-green-tea.
When it is a fault, and when it is not
A fault when it was not intended and can be brewed away — a gyokuro made with boiling water, an over-steeped green. Not a fault in young sheng pu-erh, Dan Cong or matcha, where a measured bitterness is structural and its absence would mean the tea had been made weak to hide something.
Not to be confused with
- Astringency (Mouthfeel) — A tactile sensation, not a taste: polyphenols binding salivary proteins so the mouth stops feeling lubricated.
What gets said that is not right
That bitterness and astringency are the same sensation with two names. They have different causes, different time courses and different remedies, and treating them as one is why 'brew it cooler' is given as the answer to a problem it does not touch.
Nearby
A tasting note is a comparison, not a measurement. Where the route from leaf to sensation is established it is labelled as such above; where it is not, the page says so rather than supplying a mechanism the descriptor has not earned. See the rest of the vocabulary for how the axes divide up.