A lot of people already know this, I'm sure, but it's a bit counterintuitive, and here's hoping it helps any beginners scrolling through.

This is particularly the case for pour over and drip coffee. I long assumed that an astringent flavor/feeling, sorta mouth-drying and unpleasantly mouth-watering at the same time, with a biting aftertaste, was a result of over-extraction, since it can feel sorta similar to bitterness. With that, it seemed to make sense to grind coarser, which obviously didn't help.

In the end, going significantly finer brought a much fuller and sweeter extraction, minimizing the astringency without increasing bitterness at all.

A caveat, of course, astringency can indeed come from over-extraction, so this isn't a guarantee. If you're already coarse, try finer. But if you're grinding super fine, the opposite might go for you/those beans.

TL;DR: if you are having issues with astringency, it might be intuitive to go for a lighter extraction with a coarser grind, but try going finer for richer flavor instead.