A drying, puckering sensation on the tongue and inner cheeks — the same feeling unripe persimmon or strong black tea leaves behind. It's not bitterness and it's not acidity. It's a tactile flaw, not a taste, caused by polyphenols binding to the proteins in your saliva.
In a cup, astringency reads as "this coffee feels rough" or "my mouth feels coated and sticky after I swallow." Light roasts show it more than dark, because the compounds responsible aren't roasted away.
What causes it
Mostly two things. Under-extraction of certain phenolic compounds while the rest of the cup is fine — common when the grind is too coarse, the water too cool, or the contact time too short. And green-coffee defects: under-ripe cherries picked alongside ripe ones, or beans dried too fast.
In pour-over, channeling makes it worse. Water finds a fast path through one part of the bed, drains in seconds, and pulls those rough compounds without the sweetness behind them.
How to fix it in your cup
Grind finer, raise the temperature toward 96 °C, and slow the pours so the bed has time to extract evenly. If a coffee tastes astringent across multiple recipes and grinders, the problem is the bean — switch to a different lot.
Astringency is the easiest flaw to confuse with acidity if you're new to specialty coffee. The difference is what your mouth feels twenty seconds later: bright acidity makes you salivate, astringency leaves you dry.