BrewWater
Why does my coffee taste flat or dull?
Short answer
Often the water. The World Health Organization notes demineralised water tastes flat, and producers of bottled demineralised water add minerals back for taste. Water with too little dissolved mineral gives extraction nothing to work with. Check your total dissolved solids against the target of one hundred and fifty.
| Measure | Value | Unit | Source |
|---|---|---|---|
| Target total dissolved solids for brewing water | 150 | mg/L | Specialty Coffee Association of America · verified |
| Acceptable total dissolved solids range for brewing water | 75–250 | mg/L | Specialty Coffee Association of America · verified |
| Target total alkalinity for brewing water | 40 | mg/L as CaCO3 | Specialty Coffee Association of America · verified |
Flat versus sour — they are different faults
Flat and dull usually points to too little dissolved mineral content overall, so extraction has nothing to work with. Sharp and sour points specifically at too little alkalinity, where there is not enough buffering to hold the pH steady against the acids coffee releases. The fixes differ.
What about too much mineral content?
That produces a different dullness. High alkalinity neutralises the acidity that gives coffee brightness, so the cup reads muted or chalky rather than thin. If your water is hard and your coffee tastes flat, the answer is less alkalinity, not more mineral content.
Rule the water in or out first
Before adjusting grind or ratio, brew the same coffee with water at the target figures. If the cup changes substantially, the water was the variable. If it does not, you have eliminated it and can stop chasing it — which is worth doing early, because water is the easiest variable to hold constant.