These are the two diagnostic tastes in coffee, and telling them apart is the core skill of dialling in.
Sour
Where: sides and front of the tongue. Feel: sharp, quick, puckering. Timing: hits immediately, fades fast. Compare to: lemon juice, unripe fruit, vinegar.
Sour means under-extraction. Grind finer.
Bitter
Where: back of the tongue and the throat. Feel: heavy, dry, coating. Timing: builds slowly, lingers a long time after swallowing. Compare to: dark chocolate, tonic water, over-steeped tea.
Bitter means over-extraction — or a dark roast, which is a different thing.
Both at once
Very common and very informative: it means the grind is uneven. Fines are over-extracting while boulders under-extract, in the same cup.
No grind adjustment fixes this. It is a grinder problem, and it is the main reason burr grinders beat blade grinders.
Astringency is not bitterness
Astringency is tactile — a drying, rough feeling, like strong tea or red wine tannin. It comes from over-extraction and from unripe beans.
The test
Taste a cup at three temperatures: hot, warm, and room temperature. Bitterness becomes more obvious as coffee cools. Sourness becomes more obvious hot.
Calibrate deliberately
Brew the same coffee three ways — very coarse, normal, very fine. Taste them side by side. Half an hour teaches more than months of guessing.
Last reviewed 8 August 2026