Why 'Over-Extracted' Is Usually Two Different Problems
Most troubleshooting charts treat coffee brewing as a one-dimensional tug-of-war: if the cup tastes sour, extract more (grind finer, brew hotter, wait longer); if it tastes bitter or astringent, extract less.
That mental model works across a narrow band of pour-over recipes and fails everywhere else—because a cup of coffee is governed by at least four distinct physical outputs, not one:
- Strength (
TDS %) — How concentrated the dissolved solids are in the liquid hitting your palate. - Average Extraction (
EY %) — The fraction of dry bean mass dissolved into the cup (fast organic acids first, sugars and Maillard intermediates second, slower bitter compounds last). - Evenness (
0–100) — How uniformly water contacts the coffee bed. Low evenness produces localized over-extraction alongside under-extracted pockets, yielding harshness even when average extraction sits at a textbook 20%. - Body (
0–100) — Emulsified lipids and suspended micro-fines, controlled primarily by filter media (metal mesh vs. paper) rather than soluble yield.
Interactive Regime Toy
Pressurized Percolation (Espresso Volcano Cliff)
STRENGTH
9.42%
TDS
EXTRACTION
21.4%
Avg. Yield
EVENNESS
88 / 100
Uniform flow
BODY
81 / 100
Lipids & fines
Two Regimes Where One-Axis Intuition Breaks
In pressurized espresso, Cameron et al. (Matter, 2020) showed that grinding finer increases extraction only down to a critical particle-size threshold. Past that cliff, fine particles clog local regions of the puck and force water through narrow bypass channels. Average extraction drops, while the over-flushed channel walls contribute intense astringency. A shot that tastes simultaneously sour and drying is rarely “over-extracted”—it has fallen off the fine side of the volcano curve, and the fix is grinding coarser, not finer.
In full immersion (French press, cupping, Clever), Liang, Chan & Ristenpart (Scientific Reports, 2021) demonstrated that once steep time is sufficient, extraction approaches a desorption equilibrium ceiling governed almost entirely by the water-to-coffee ratio. Chasing higher sweetness by grinding immersion coffee ultra-fine mostly adds suspended fines and muddiness without moving the equilibrium ceiling; adjusting the brew ratio moves both strength and extraction predictably.
I built Dialed to make all four axes visible at once across immersion, pour-over, espresso, moka pot, and cold brew—linking every parameter directly to the underlying literature (or marking empirical assumptions explicitly).