Why does my coffee taste bitter?
Usually over-extraction: water has been in contact with the grounds for too long, or at too high a temperature, or the grind is too fine — so the process has pulled out compounds that should have been left behind.
Brewing coffee is a sequence. The pleasant acids and fruit notes dissolve first, then the sugars and balanced flavours, and finally the bitter compounds, including some tannins and the darker roasting products. Stop too early and the cup is sour, thin and under-developed. Go too far and bitterness dominates. The target is the middle.
So the fixes are the variables that control contact:
- Grind coarser. Finer grounds have more surface area and extract faster. This is the single most effective adjustment for most people.
- Shorten the brew. For a cafetière, four minutes is a common target; leaving it to stand while you drink the first cup keeps extracting.
- Cool the water. Boiling water is too hot. Around 92–96°C is the usual range, so a kettle left for thirty seconds after boiling.
- Use less coffee, or more water, if the ratio is very strong.
Two other causes are worth ruling out. Stale or dirty equipment contributes real bitterness — old coffee oils go rancid, and a machine that has never been descaled or a cafetière with residue in the mesh will taint every cup. And a very dark roast is bitter by design; no brewing adjustment will make a French roast taste bright.
Sourness and bitterness are often confused. Sour means under-extracted — grind finer or brew longer, the opposite advice.