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Astringency

The dry, puckering, slightly rough feeling tea leaves behind on the tongue and the roof of the mouth. It is the quality most often mistaken for bitterness, and separating the two is the single most useful thing a new taster can learn.

Sensed as
mouthfeel
Compounds
catechins, and their oxidation products theaflavins and thearubigins
Rises with
hotter water, longer steeps, more leaf, later infusions
Falls with
cooler water, shorter steeps, a quick rinse

What it is

A drying sensation rather than a flavour. Your mouth feels less slippery than it did a moment ago, and surfaces that normally glide over each other start to catch. Strong astringency in a young sheng or an over-steeped Assam can make the sides of the tongue feel almost furred. It builds across a session rather than arriving at once, so the third cup often reads as more astringent than the first even when the brew was identical.

Where it comes from

Catechins, and the theaflavins and thearubigins they turn into during oxidation. They interact with proteins in your saliva, and the classic explanation is that they precipitate those proteins and strip the mouth of lubrication. That is part of it and not all of it: anaesthetising the taste nerve alone leaves astringency perfectly intact, which is how we know the sensation travels on the trigeminal nerve rather than the taste nerves, and small polyphenols produce astringency without measurably changing how well saliva lubricates. So at least some of what you feel is a receptor responding, not just a mouth drying out.

Which teas show it

Strongest in young sheng puer, in unshaded green teas brewed hot, and in brisk black teas from Assam and Ceylon, where it is a wanted quality rather than a fault. Lowest in well-aged shou puer, in heavily roasted oolongs and in shaded Japanese greens, where high theanine and low light shift the leaf away from catechin production. See the style pages for how far this varies inside a single category.

How to turn it down

Cooler water first, since catechin extraction climbs steeply with temperature. Ten degrees can do more than ten seconds. Then shorten the steep, and if it is still drying, rinse the leaf briefly and discard that water. More leaf and less time gives you strength without the drying, which is the whole logic of gongfu brewing and the reason a short heavy steep tastes fuller and softer than a long light one.

How to turn it up

Hotter water and longer steeps, in that order. A tea that has gone flat and thin across a session often has astringency left in it that only a hotter, longer pour will reach.

What it gets confused with

Bitterness, constantly. The test is where you notice it: bitterness is a taste, so you register it while the liquor is in your mouth and it fades once you swallow. Astringency is a texture, so it arrives late, sits after the swallow and gets stronger over the next few seconds. If your mouth feels dry thirty seconds later, that was astringency. Also confused with body, because a strongly astringent tea feels like it is doing more in the mouth than it is.

What people get wrong

Calling it tannin. Tea does contain condensed polyphenols, but the hydrolysable tannins that word means in wine and oak are a different class of molecule, and the advice that travels with the word does not transfer. Decanting will not soften a tea, and tea's polyphenols do not behave like wine's in the mouth or in the body. The second mistake is treating astringency as a defect. In a young sheng or a first flush Darjeeling it is structure, and a version with none is usually a version with nothing else either.

If this is your problem

teabert, the tealytics teapot, keeper of the kettle
If your mouth is still dry half a minute after you swallowed, that was not bitterness. Rate it here instead.

Sources