Particle Distribution and Uniformity
A grind is never a single size — it is a distribution of sizes around a target. Plot how many particles fall at each diameter and you get the grinder's signature curve. The shape of that curve, not just its center point, decides how evenly your coffee extracts. This is why two grinders set to the "same" medium can brew very differently: their distributions differ.
#Reading the Curve 📈
The key feature is the number of peaks. A unimodal distribution has one clear hump — most particles cluster near the target size, with few strays. A bimodal distribution has two humps — a main peak at the target plus a second, smaller peak of very fine dust (fines). Almost every real grinder produces some fines, so distributions are rarely perfectly unimodal; the question is how tight the main peak is and how large the fines tail.
| Distribution | Shape | Extraction behavior |
|---|---|---|
| Unimodal (tight) | One narrow peak | Even — particles extract in step |
| Bimodal | Main peak + fines peak | Uneven — fines and boulders diverge |
| Wide / flat | Spread out | Chaotic — see blade grinders |
#Why Uniformity Matters 🎯
Extraction is a race against time, and every particle extracts at a rate set by its size. In a brew, all particles get the same contact time — so if they differ wildly in size, they cannot all finish in the right place. The fines over-extract into bitterness while the boulders under-extract into sourness, and the cup is the muddled average of both. A uniform grind lets you choose one contact time that suits nearly every particle, so the whole bed lands in the sweet spot of extraction together. That is the mechanism behind clean, sweet, well-defined pour over.
Much of the price difference between grinders buys a tighter distribution — sharper, better-aligned burrs that produce fewer strays. It is the main reason a good grinder out-brews a good dripper.
A modest population of fines is not pure evil. Fines add body and help build the bed's resistance to flow. The goal is controlled distribution, not zero fines — which no grinder achieves. Chasing perfection here has diminishing returns past a quality burr set.
#Geometry and Distribution
Burr geometry nudges the curve: many flat burrs aim for a tighter unimodal peak, while conicals are sometimes described as slightly broader — though, as that note stresses, this is contested and grinder quality dominates the category.
#Continue Reading
- Fines and Boulders — the two ends of the distribution
- Burr Grinders vs Blade Grinders — why blades wreck the curve
- Conical vs Flat Burrs — how geometry shifts the peaks
- Channeling and Uneven Extraction — what uneven grind does in the bed
- Why Grind Size Matters — size and spread together