Sour or bitter? Fix it with the grinder
The rule of thumb
- Sour, thin: under-extracted → grind finer.
- Bitter, harsh: over-extracted → grind coarser.
Change one thing at a time (grind size first), and keep dose and water constant.
Why burrs help
Burr grinders produce a more even particle size than blade grinders, which is why they are the usual recommendation.
General brewing guidance, not a test result.