Grind size

Average diameter of coffee particles after grinding, expressed in microns or grinder steps. Coarse grind (≥900µm) suits French press; fine grind (200-400µm) suits espresso. Wrong setting causes over- or under-extraction.

Background & Context

Grind size is the average particle diameter of ground coffee, measured in microns. It is the primary extraction control variable across all brewing methods — a finer grind increases surface area contact between coffee and water, accelerating extraction rate; a coarser grind decreases surface area, slowing extraction. The relationship is non-linear: a 10% change in grind setting can produce a 15–25% change in extraction yield depending on the method and the coffee. In espresso, the extraction window is so narrow — fine adjustments of 0.1mm on the grinder ring — that a single grind setting day-to-day can differ significantly as the burrs heat up, seasonal humidity changes, or a new bag of coffee is opened. In filter brewing, the acceptable grind range is broader: coarse (French press, 800–1200 microns), medium-coarse (Chemex, 700–900 microns), medium (V60, Kalita Wave, 600–800 microns), medium-fine (AeroPress, 500–700 microns). Grind size is also the variable most affected by burr calibration and grinder quality: inconsistent particle size distribution — a wide range of sizes from the same grinder — produces uneven extraction (some particles under-extracted, others over-extracted simultaneously).

Practical Use

The most impactful grind change advice: never use a blade grinder for specialty coffee. Even a basic burr grinder ($60–80) produces dramatically more consistent particle sizes than any blade grinder. For dialing in espresso: adjust grind size first before any other variable. Coarser = shorter, faster, more sour shot. Finer = longer, slower, more bitter shot. For filter: if the coffee drains too fast (under 2 minutes for V60), grind finer. If too slow (over 5 minutes), grind coarser.

Related Terms

Related terms: Burrs — the grinding elements that determine grind size distribution. Extraction yield — grind size is the primary EY control variable. Espresso extraction — most sensitive to grind size changes. Channeling — coarse grind in espresso is a channeling risk.