Brewing dissolves flavour out of ground coffee. How much gets dissolved is called extraction. Get it right and the cup is sweet and balanced.
The levers
- Grind size: finer extracts more, coarser less.
- Time: longer contact extracts more.
- Temperature: hotter water extracts more.
- Ratio: more water per gram of coffee extracts more, and also dilutes.
Sour cup? Go finer or longer. Bitter cup? Go coarser or shorter. Change one thing at a time.