Green Coffee Screen Size & Density: A Roaster's Guide (Part 1 of 2) 

A cupping score tells you how a coffee tastes. It doesn't tell you how it will roast, how long it will hold its flavor, or whether it's worth the price on the contract. For that, you need to look at the physical grade of the green coffee itself.

Physical analysis of green coffee comes down to four things: screen size, density, moisture content (and water activity), and defect count. This post covers the first two, screen size and density, since both are measurements of the bean's structure, and both directly predict how a coffee behaves in the roaster. Part 2 covers moisture, water activity, and visual defects.

Screen Size: Bigger Doesn't Mean Better

Screen size is sorted at the dry mill, before the coffee is bagged for export. Machines use sloped, perforated screens that vibrate and shake beans through progressively smaller holes, separating coffee by size.

Sizes are measured in 1/64-inch increments, a "screen 16" bean is 16/64 of an inch across. To grade a sample, mills run about 350 grams of coffee through a stack of screens (roughly size 20 down to size 13 or 14), agitate it for 30 seconds, then weigh what's retained on each screen to get a size breakdown.

Naming conventions vary a lot by origin, which trips up a lot of buyers new to a region:

• British system (Kenya, Tanzania, Zambia, India, PNG): grades like E, AA, AB, C, PB, T
• Colombia: Supremo, Excelso, UGQ (unclassified coffees have been sold this way since 2015)
• Central America: EP, AP, SHB/SHG (Strictly/Hard Bean or Strictly/Hard Grown, tied to elevation as much as size)
• Brazil: numerical screen sizes (17/18, 14/15/16) combined with cup-quality terms like Strictly Soft or Soft

Here's the part worth remembering: screen size has never been a reliable stand-in for cup quality. Larger beans have historically traded at a premium, Kenya AA sells higher than AB, but that's a market habit, not a quality guarantee. Coffees from Nariño in Colombia, Nyamagabe in Rwanda, and Gedeo or Sidama in Ethiopia routinely produce smaller beans that score exceptionally well. Some of the best specialty coffee in Ethiopia is also some of the smallest.

Peaberries are the clearest exception to "bigger is better." A peaberry is a genetic anomaly where the cherry develops one round seed instead of the usual facing pair. They're not a quality indicator either way, but they do carry their own mystique, and their own market (Tanzania in particular has built a reputation around them).

Why size matters at the roaster?

Surface-area-to-volume ratio determines how fast a bean absorbs heat. Coffee with a uniform screen size roasts evenly. A mix of sizes in the same batch roasts unevenly, since smaller beans heat faster than larger ones under the same profile. If you want to know whether size is actually affecting your cup, the test is simple: separate a coffee by screen size, roast each on an identical profile, and cup them side by side. In practice, screens 16–17 tend to taste clean; screens 14 and below more often show green or underripe notes at the table, but that's a tendency, not a rule, and it depends entirely on the lot.

Density: The Number That Predicts How Coffee Roasts

Density is mass divided by volume, usually expressed in grams per liter. Coffee gets sorted by density more than once on its way to your roaster, cherry flotation at the wet mill (used in places like Rwanda and Burundi to catch underripe or insect-damaged cherries), grading channels after depulping (floaters vs. sinkers, with sinkers generally tasting better and pricing higher), and density tables at the dry mill, which vibrate at a set angle and frequency to separate low-density beans and foreign matter from the good coffee. Not every defect shows up this way, though, some, like the potato defect covered in Part 2, stay hidden until the coffee is actually roasted.

Regional patterns worth knowing

East African coffees (Ethiopia, highland Kenya) tend to run dense. Southern Colombian departments (Nariño, Cauca, Huila) trend dense as well. Sumatra and Brazil tend to run lower density. In general: higher elevation and smaller screen size correlate with higher density, washed coffee is denser than natural, and drier coffee is denser than wetter coffee.

How it's measured?

The simplest method is free-settling (bulk) density, fill a container of known volume with green coffee, weigh it, and calculate grams per liter. You can do a rough version of this with something as basic as a 7.5 fl oz glass. The alternative, displacement density (submerging beans in water), is more precise on paper but ruins the sample, is thrown off by surface tension, and isn't practical for routine use. Free-settling density is also more representative of how the coffee is actually handled and shipped, which is the number that matters for roasting decisions.

Why it matters financially?

Denser coffee takes up less space per kilogram. A coffee at 680 g/L needs meaningfully less container or warehouse space than one at 640 g/L to hold the same weight, roughly 6% less, in that example. In a business where shipping and storage space is a real cost, density translates directly into value per shipment.

There's also a common misconception that low density means a coffee was shipped "wet" to pad the weight. In practice, the opposite tends to show up in the data: across specialty lots, higher density and lower moisture usually move together, not apart, more on that in Part 2.

Roasting implications: think of a dense coffee like a cast iron pan and a low-density coffee like a lighter skillet. The dense coffee takes more energy to get going but holds and conducts that heat more steadily through the roast, which usually means a more gradual temperature increase early on. And density isn't fixed: by first crack, a bean has already lost roughly half its original density as it expands and drives off moisture.

Coming Up in Part 2

Screen size and density tell you a lot about how a coffee is likely to behave in the roaster. What they don't tell you is whether that coffee is going to hold its flavor by the time it reaches you, or whether it's hiding defects that are going to show up in the cup. That's what Part 2 covers: moisture content, water activity, and the visual defects worth checking for before you roast.

If you're sourcing and want coffee that's been graded and handled with this level of attention, check out our latest offerings here, or send us a message and we'll walk you through the specs on any lot you're considering.