Under-extraction means too little of the coffee’s soluble material dissolved.
What it tastes like
Sour — sharp, thin, quick to fade, without sweetness behind it.
Salty, oddly. Under-extracted coffee often reads as saline, because acids and salts come out early and the sweetness that would balance them has not arrived.
Thin body and a short, empty finish.
Why it happens chemically
Extraction is sequential. Acids and salts first, then sugars, then bitter compounds. Stop too early and you have only the first group.
The numbers
Below 18% extraction yield is generally under-extracted.
The causes
Grind too coarse. Less surface area. The commonest cause.
Contact time too short. An espresso gushing in 12 seconds, a pour-over draining in 90.
Water too cool. Under 90 °C (194 °F), extraction slows significantly. This is why cheap machines make sour coffee.
Uneven wetting. Dry patches in the bed are not being extracted at all — channeling in espresso, a poor pour in a V60.
Water too soft. Distilled or very soft water lacks the minerals that carry flavor compounds out.
The fixes
Grind finer. Then hotter. Then longer.
The freshness factor
Very fresh coffee — under four days — degasses hard, and the gas physically blocks water from the grounds. That reads as under-extraction and resolves on its own.
Last reviewed 30 October 2026