The grind is most of it
If I could keep only one variable to adjust, I’d keep the grind and throw the rest away. More bad cups are a grind problem wearing a disguise than anything else.
The two faults have clear tastes once you’ve met them:
Sour, thin, watery
Under-extracted. The water ran through too fast and didn’t pull enough out of the grounds. Go finer — one notch — which slows the flow and extracts more. This is the more common fault with a fresh light roast.
Bitter, drying, hollow
Over-extracted. The water sat too long or the grind was too fine, and it pulled out the harsh end of the coffee. Go coarser, one notch.
- Too fast & sour
- grind finer
- Too slow & bitter
- grind coarser
- Change
- one notch, then taste
The discipline that makes this work is changing exactly one notch and brewing again before touching anything else. If you move the grind and the dose and the temperature together, a better cup teaches you nothing, because you don’t know which change earned it. Dull, patient, and it works.