Under-Extraction
萃取不足
GrindingDefinition
The opposite failure, in which water leaves the grounds before enough flavor has dissolved, so the cup lacks sweetness and body. It usually traces to too coarse a grind, a brew that finished too fast, water that is too cool, or simply too little coffee relative to the water. The telltale taste is sharp, sour, thin, and faintly salty - like a coffee that never finished brewing.
Etymology
The prefix under-, meaning insufficient, paired with extraction; it entered common use alongside over-extraction as specialty roasters shifted toward lighter, harder-to-dissolve beans.
In use
The verdict on a sour, watery shot - 'grind finer, it's under-extracted' - and the most common first hurdle when dialing in espresso.