Over-extraction

Extraction exceeding 22% EY, producing a bitter, astringent, dry cup. Causes: too fine grind, too high temperature, too long time, excessive agitation. Correction: coarser grind or shorter time.

Background & Context

Over-extraction occurs when too much of the available soluble material has been dissolved from the coffee grounds, resulting in a cup dominated by harsh, astringent, and bitter compounds. On the Brewing Control Chart, over-extraction is defined as an extraction yield above 22% for filter coffee. The chemistry: coffee compounds dissolve in a specific sequential order. The first to extract are positive compounds — acids, sugars, and fruity aromatics (extractable between 18–22% EY). Beyond this point, the next compounds to dissolve are bitter phenylindanes (from chlorogenic acid degradation) and astringent tannins — the source of over-extraction's characteristic dry, harsh, metallic aftertaste. Over-extraction tastes simultaneously bitter and hollow — the sweetness of the middle-extraction range has given way to harsh, drying compounds with no structural support. In espresso, over-extraction results from shots that run too long (above 35 seconds), are too finely ground relative to the dose, or are brewed at too high a temperature. In filter coffee, over-extraction occurs with too fine a grind, too long a brew time, or too high a temperature. The salt trick: adding a small pinch of salt suppresses bitter receptors — if this dramatically improves a coffee, it confirms over-extraction.

Practical Use

Diagnosing over-extraction vs. under-extraction: under-extraction = sour, weak, lacking sweetness; over-extraction = bitter, astringent, dry, hollow. Both can taste bad, but differently. To fix over-extraction in filter: coarsen the grind (first fix), reduce brew temperature, or reduce steep time. In espresso: coarsen the grind (the most direct fix), or reduce temperature to 88–89°C for dark roasts that are especially prone to phenylindane extraction.

Related Terms

Related terms: Under-extraction — the opposite defect. Extraction yield — over-extraction = EY above 22%. Bitterness — the dominant sensory signal of over-extraction. Brewing Control Chart — the tool for targeting correct extraction zones.