Over-extraction means too high a proportion of the coffee’s soluble material has dissolved into the water.
What it tastes like
Bitter, obviously — but bitterness alone can also come from dark roasting.
The reliable signs are astringency — a drying, mouth-puckering sensation like strong tea — and a hollow, empty finish. Over-extracted coffee is bitter and then nothing.
The pleasant compounds come out first; what comes out last is bitter and drying.
The numbers
Extraction yield is measurable. 18 to 22% is the accepted good range. Above 22% is generally over-extracted, though the boundary moves with the coffee.
Measuring it needs a refractometer. Tasting it needs practice and nothing else.
The causes, in order of likelihood
Grind too fine. More surface area, faster extraction. The commonest cause and the first thing to change.
Contact time too long. A four-minute press left for ten, or a pour-over that has stalled.
Water too hot. Over 96 °C extracts aggressively.
Too much agitation. Excessive stirring or pouring extracts more.
Ratio too wide. 1:20 pulls more from the same coffee.
The fixes
Grind coarser first. Then shorten the time. Then lower the temperature.
The trap
Over-extracted and under-extracted at once is possible and common — it means the grind is uneven, and that is a grinder problem.
Last reviewed 8 August 2026