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.
I think jumping coarser and then “fine” tuning (pun half-intended) works well IF you start super fine.
If you’re starting in the middle of the spectrum from fine to coarse, and you only ever try going coarser first, you never get to try what might be the best cup, which may be on the finer side of your starting point.
Winning cups in pour over competitions are often ground shockingly fine, like only 30%-50% coarser than espresso fine. You may be using dark roast or Ethiopian beans (known to produce tons of fines and need coarser settings), but if not, I’d really suggest going finer just to see how it goes. You’ll find a lot of experts suggest the same.