As·trin·gen·cy

The dry, puckering sensation on the tongue, often from tannins. A hint of it is a mark of a well-made tea.

Astringency is the same drying, numbing sensation you get from biting into an unripe banana or persimmon — caused by tannins binding to proteins in saliva. In tea, it's a texture rather than a flavour, and it's not inherently a flaw.

A well-made tea often carries a light astringency that frames the other flavours and leaves a long, structured aftertaste. Too much, usually from over-steeping or water that's too hot, can tip a tea from pleasantly brisk into simply bitter and drying.