How Grind Distribution Changes Extraction (and Why Grind Size Alone Doesn't Tell the Full Story)

When you grind coffee, you're not producing particles of one size. You're producing a distribution of particle sizes — some larger, some smaller — centered around whatever average your grinder is set to.

That distribution matters more than the average size does. Two coffees ground to the same nominal size can extract very differently, because the spread of particles around that average changes how water moves through the bed of grounds and how the soluble compounds come out.

This is what grind distribution is, why it matters, and how different grinders produce different distributions.

What grind distribution actually means

Grind distribution is the range of particle sizes produced when you grind coffee. A "medium" grind isn't actually all medium particles. It's a curve — some particles are coarser than the target, some are finer, and most are somewhere in the middle.

A typical grinding curve for a common burr grinder at a "medium" setting looks something like this:

• 30 to 40% of particles are at the target size or very close to it.
• 20 to 30% are finer than the target.
• 20 to 30% are coarser than the target.
• A small percentage are very fine (called "fines"), typically much smaller than the average.
• A small percentage are very coarse (called "boulders"), typically much larger than the average.

Different grinders produce different distributions at the same nominal setting. A high-quality flat-burr grinder might produce 70 to 80% of particles at or near the target, with relatively few fines and boulders. A low-quality conical burr grinder might produce a wider distribution, with more fines and boulders for the same nominal setting.

That difference matters because the fines and boulders extract very differently from the bulk of the grind.

Why fines and boulders matter

Fines are particles that are much smaller than the target grind size. They extract much more quickly than the rest of the bed because they have a much higher surface-area-to-volume ratio. In a typical pour-over brew, fines can extract 25 to 35% of their mass while the rest of the bed extracts 18 to 22%.

What this means in practice is that fines contribute disproportionate bitterness to the cup. They're the source of most of what people describe as "harsh," "astringent," or "dusty" in a brewed coffee.

Boulders are the opposite. They're particles much larger than the target, and they under-extract — sometimes significantly. They contribute less to the cup than they should given their mass, and they leave the brew tasting thin or underdeveloped.

A grinder that produces many fines will produce a cup with more bitterness than the same coffee ground through a grinder that produces fewer fines. A grinder that produces many boulders will produce a cup that tastes underdeveloped and weak.

How grinders compare

Grinders vary widely in distribution, and the most reliable way to characterize a grinder is to look at the particle-size distribution it produces rather than its nominal setting.

High-end flat-burr grinders (like the Mahlkonig EK43, the Mahlkonig E80, or the Ditting 804) tend to produce the tightest distributions. Particle sizes cluster tightly around the target, fines are minimized, and the cup is generally cleaner and more consistent.

Mid-range conical-burr grinders (like the Baratza Forte, the Niche Zero, or the Eureka Mignon Specialità) produce distributions somewhere between flat-burr and entry-level. The Niche in particular is known for relatively few fines for a conical grinder, which is one reason it's popular for filter brewing.

Entry-level burr grinders (like the Baratza Encore or the Breville Smart Grinder Pro) produce wider distributions. The Encore is well-regarded for what it costs, but it produces more fines than more expensive grinders, particularly at finer settings.

Blade grinders produce the widest distributions by far. They chop rather than grind, and the result is unpredictable particle sizes ranging from coarse fragments to fine dust. This is why blade grinders are almost universally considered the wrong tool for brewing — the distribution is too wide, fines dominate, and the cup is consistently harsher than it would be with a burr grinder.

What this looks like in the cup

In a pour-over brew, the practical differences between grinders show up as follows.

A grinder with tight distribution (flat-burr, high-end) will produce a brew where the cup profile is consistent across pours. You'll taste clarity in the cup — individual flavor notes will be distinct, and there's less "muddy" quality from uneven extraction. Acidity is brighter, body is lighter, and the finish is cleaner.

A grinder with wide distribution (entry-level burr, blade) will produce a brew where the cup profile has more shadow and edge. Individual flavor notes blur together, the body often reads as heavier (because of all the extraction from the fines), the finish tends to have more bitter residue, and the cup feels less refined.

Both cups can be perfectly drinkable. The difference is that the tight-distribution cup is more reliable and the wide-distribution cup is harder to dial in. If you're chasing a specific flavor profile in a coffee, the tighter distribution gives you more control.

What this means for brewing at home

If you're buying a grinder for home brewing, the distribution is one of the most important things to consider. Here's a practical rule of thumb.

For pour-over and other filter brewing, distribution matters most. A mid-range burr grinder with a tight distribution will give you a noticeably cleaner cup than a less expensive burr grinder with a wider distribution, even if the nominal grind setting is the same.

For espresso, distribution matters in a different way. Espresso brewing is sensitive to the coarse end of the distribution more than the fines (because too many coarse particles can lead to channeling and uneven extraction under the higher pressure), and a grinder that's solid for espresso may still produce an unforgiving brew for pour-over.

For French press, distribution matters least. The long steep time and full immersion give the brew more tolerance for an uneven distribution, and a less expensive grinder will produce a perfectly drinkable French press.

The takeaway

Grind size is a useful starting point but it doesn't tell the whole story. The distribution of particles around that average size changes how coffee brews, and grinders that produce tighter distributions tend to produce cleaner, more consistent cups.

If you're choosing a grinder, look for reviews that discuss particle-size distribution rather than just nominal settings. The grinder that produces 75% of particles at the target size and minimizes fines will generally give you a more consistent cup than one that nominally grinds to the same size but produces a wider spread.

This is what grind distribution is, why it matters, and how to think about it when you're choosing a grinder.

Brew slow.