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Fine vs coarse grind on a V60, measured

One variable changed · simulated on the CoffeeScope V3 engine · updated 18 July 2026

Grind size is the single most powerful dial on a pour-over, and the debate is old: grind finer to pull more out of the bed, or coarser to keep the cup clean and avoid bitterness? We ran both through the CoffeeScope simulator on one identical V60 recipe — changing only the grind — and measured what came out of the bed.

The question

A finer grind exposes more surface area, so each ground gives up its solubles faster; it also produces more fines that pack the bed and slow the water down, extending contact time. Both effects push extraction up. Coarser grind does the opposite: less surface, a looser bed, faster drawdown, less extracted. The barista's worry is that fine over-extracts into bitterness and astringency, while coarse under-extracts into a thin, sour cup. This experiment puts numbers on that trade.

The setup

Both lanes are the baked Hoffmann Ultimate V60 recipe (15 g, 1:16.7, 96 °C, center pour). The only difference is grind median — 450 µm vs 850 µm — with the simulator's fine/medium/coarse size-class model enabled so fines can migrate and clog the paper.

Exact recipe (reproducible in the simulator)

{
  "brewer": "v60", "doseG": 15, "ratio": 16.7,
  "waterTempC": 96, "roastLevel": 0.28, "roastAgeDays": 7,
  "grindSpread": 0.24, "bloomWaterX": 3, "bloomTimeS": 45,
  "pourRate": 6, "pourHeight": 16, "pourPattern": "center",
  "bedLevel": 0.5, "pourHeadroom": { "stopMm": 10, "resumeMm": 13 },
  "sizeClasses": true, "resolution": "medium", "numericBackend": "js",

  "grindUm": 450   // Lane A — fine
  "grindUm": 850   // Lane B — coarse
}

Every number on this page is read from these two runs, taken to brew completion (the drawdown stall detector) on the deterministic V3 engine.

Measured results

Measure	Fine · 450 µm	Coarse · 850 µm	Takeaway
Extraction yield (EY)	23.9 %	17.1 %	Fine over-extracts past the ~18–22 % Gold Cup window; coarse falls short of it.
Strength (TDS)	1.61 %	1.15 %	Fine brews a markedly stronger cup; coarse lands at the thin edge of filter strength.
Drawdown time	424 s	154 s	Fines cake the paper: the fine bed drains nearly 3× slower, which itself drives more extraction.
Cup volume	223.5 ml	223.4 ml	Same water in, essentially the same beverage out — grind changes concentration, not volume.
Cup temperature at finish	55.8 °C	77.2 °C	The 7-minute fine drawdown loses a lot of heat before it reaches the cup.
Caffeine	172 mg	152 mg	Tracks contact time here — the long fine brew strips more; caffeine is otherwise grind-insensitive.

Predicted taste axes

The simulator's six taste axes (plus astringency) are directional calibrations, not sensory-panel scores. A difference is flagged tasteable when it clears the model's own threshold of 0.045 (0–1 scale).

Axis	Fine	Coarse	Δ	Tasteable?
Bitterness	0.68	0.26	0.42	yes — the headline difference
Clarity	0.49	0.82	0.33	yes — coarse reads far cleaner
Astringency	0.28	0.04	0.23	yes — fines dry the fine cup out
Aroma	0.76	0.97	0.21	yes
Sweetness	0.41	0.58	0.17	yes — bitterness masks sweetness in the fine cup
Acidity	0.47	0.58	0.12	yes
Body	0.63	0.56	0.08	yes

Every axis moves past the tasteable threshold — grind is the one variable in this set where the whole flavour profile shifts at once.

How it builds over time

Cumulative extraction yield and cup volume, sampled during the brew:

Time	Fine — EY	Fine — in cup	Coarse — EY	Coarse — in cup
60 s	9.5 %	24.6 ml	8.6 %	47.8 ml
120 s	16.0 %	51.1 ml	14.9 %	157.0 ml
Final	23.9 %	223.5 ml	17.1 %	223.4 ml

At one minute the coarse bed has already passed nearly twice as much liquid to the cup (47.8 vs 24.6 ml): the clogged fine bed is the real engine of over-extraction, not surface area alone.

Why it happens

Two mechanisms compound. First, surface area: the extraction kinetics scale with grind surface, so finer grounds hand over their fast and slow solubles more quickly per second of contact. Second, and larger here, permeability: bed permeability follows a Kozeny–Carman shape that scales with the square of grind size (k ∝ d²), and the finest particles migrate down and cake against the paper. The fine bed's drawdown stretches from 154 s to 424 s, and that extra contact time keeps pulling slow, bitter polyphenols long after the sweet fast compounds are spent — which is exactly why the fine cup lands at 23.9 % EY with high bitterness and astringency, while the free-draining coarse bed stops at 17.1 % and stays clean. See the methodology for the Darcy/Kozeny–Carman and two-timescale extraction models this rests on.

Caveats

This is a simulator, not a measurement of your grinder and your beans. Read the numbers as a well-reasoned direction, not a lab result.

The taste axes are calibrated to move the right way by a plausible amount, not validated against a trained sensory panel (see the calibration note).
Real grinders produce a whole particle distribution with a fines tail specific to the burr; the model uses a median plus a fixed spread and a three-class fine/medium/coarse split, not your grinder's true curve.
The clog model is a tuned fines-caking throttle on the paper, not a resolved particle-by-particle filter — it captures the direction and rough magnitude of the slow-down, not an exact seconds figure for a specific paper.
Channeling or paper-wall bypass — a common real-world cause of uneven fine extraction — is not modeled.

Run it yourself

Load this exact A/B in the live simulator and slice the rig open to watch the fine bed clog and the drawdown stall:

Run fine vs coarse live →

Related experiments: Light vs dark roast 1:14 vs 1:17 ratio 85 °C vs 96 °C

Methodology, validation & limitations →