Understanding Coffee Bean Grading: What AA, AB, C, and Peaberry Really Mean
Coffee is a natural product, and like all things grown in nature, no two beans are exactly alike. Some are larger, some smaller, some rounder, some more elongated. To bring consistency to the trade and roasting process, producers and buyers have long relied on coffee bean grading systems – with bean size being one of the most common metrics.
How Are Coffee Beans Graded by Size?
Globally, coffee beans are sorted using a system of grading sieves – imagine a stack of flat colanders, each with slightly smaller holes than the one above. Beans are poured in at the top, and as they fall through the stack, they're sorted by the smallest sieve they can pass through.
These screens are typically measured in 1/64ths of an inch:
- Screen 18 = 18/64" (7.14 mm)
- Screen 16 = 16/64" (6.35 mm)
- Screen 14 = 14/64" (5.56 mm)
Why does size matter? Larger beans often correlate with higher altitude, slower maturation, and more developed sugars – though this isn't a hard rule. Size grading also helps ensure even roasting, as similarly sized beans roast at similar rates.
Kenya's Unique Coffee Grading System
Kenya uses the same screen sizes but applies a letter-based grading system:
| Grade | Screen Size | Description |
|---|---|---|
| AA | 17–18 | Largest beans, often prized for complexity and brightness |
| AB | 15–16 | Medium-sized, balanced profile |
| C | 14 and below | Smaller beans, often used in blends or commodity coffee |
| PB (Peaberry) | Varies | A single, round bean formed when only one seed develops inside the cherry |
What Is a Peaberry?
Most coffee cherries contain two seeds (beans), which flatten against each other. Occasionally, only one seed develops – resulting in a peaberry. These beans are rounder, denser, and often considered to have a more concentrated flavour.
Peaberries are typically separated during grading because their shape allows them to pass through screens differently. They also roast differently due to their density and shape, often requiring slightly lower charge temperatures and longer development times in the roaster.
One Farm, Many Grades: Kiriga as a Case Study
Coffee grading isn't just a national standard – it can vary within a single farm. A great example is Kiriga Estate in Kenya.
From a single harvest, Kiriga has produced multiple grades:
- AA – Large, dense beans with vibrant acidity and floral complexity
- AB – Balanced and versatile, with juicy fruit notes
- C – Smaller beans, but surprisingly sweet and clean
- Peaberry (PB) – Round, dense beans with a syrupy body and intense flavour
This diversity comes from post-harvest processing, not different trees. After pulping and washing, the beans are dried and then passed through screens to separate them by size.
Last year, we were lucky to offer all four grades from Kiriga. This year, we're focusing on two standout lots:
- Kiriga AA – Blackcurrant, rhubarb, cream
- Kiriga Peaberry – Blackberry jam, lime marmalade, dried apricot
Even though AB and C aren't available this season, the AA and PB lots continue to showcase the range and quality that a single farm can produce. If you'd like to find out more about our relationship with the Kiriga Estate, read our Kiriga producer story.
Grading Systems Around the World
Other countries use different coffee grading systems based on size, defects, or cup quality:
- Brazil – Uses screen size and defect count (e.g. NY 2/3, screen 17/18)
- Colombia – Grades by size: Supremo (larger), Excelso (smaller)
- Ethiopia – Uses a numbered grading system based on cup quality and defect count (see below)
- Indonesia – Uses a defect-based system: Grade 1 (0–11 defects), Grade 5 (86+)
- SCA (Specialty Coffee Association) – Defines Grade 1 as having no primary defects and a cupping score of 80+
Coffee Grading Sieves
Click any screen size to see which grades it produces
Grading Systems Around the World
Select a country to explore its grading system
Ethiopia: Coffee Grades 1 to 5
Click a grade to learn what it means in practice
Ethiopia's Coffee Grades 1 to 5
Ethiopia's grading system deserves a closer look — particularly if you buy single origin coffees and want to understand what those numbers mean.
The Ethiopian Coffee and Tea Authority grades washed (wet-processed) coffees on a scale from Grade 1 to Grade 5, based primarily on cup quality and defect count:
| Grade | Defects (per 300g sample) | What it means |
|---|---|---|
| Grade 1 | 0–3 | Specialty grade — clean cup, exceptional flavour, minimal defects |
| Grade 2 | 4–12 | Still high quality; most traceable specialty lots fall here |
| Grade 3 | 13–25 | Commercial grade; acceptable cup quality |
| Grade 4 | 26–45 | Lower commercial grade |
| Grade 5 | 46+ | Commodity grade; used in blends or instant coffee |
Natural (dry-processed) Ethiopian coffees follow a parallel but separate grading scale, with slightly different defect tolerances. In both cases, Grade 1 is the benchmark for specialty coffee — which is why you'll often see it referenced on bags and tasting notes for high-end Ethiopian lots.
It's worth noting that cup quality is assessed alongside defect count: a coffee can have very few defects but still score poorly in the cup. Grade 1 requires both.
Final Thoughts
Coffee grading by size is just one piece of the puzzle — but it's a fascinating one. It helps producers sort their harvests, buyers make informed decisions, and roasters fine-tune their profiles. And as Kiriga shows, even a single farm can offer a diverse spectrum of flavours through careful grading and selection.
Curious about how coffee processing affects flavour before grading even begins? Explore the rest of our processing guide for a fuller picture — or browse our current single origin coffees to see grading in practice.