What is coffee grading?

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 sieving screens – 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 screen 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:

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, please read our Producer Story by clicking here.

Grading Systems Around the World

Other countries use different 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 – Grades by cup quality: Grade 1 (washed, clean), Grade 2, etc.
  • 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+

Other Products Graded by Size or Quality

Coffee isn’t the only product where grading matters. Here are a few others:

  • Wine grapes – Graded by sugar content (Brix), size, and ripeness
  • Eggs – Graded by weight and shell quality (e.g. Class A, Medium, Large)
  • Beef – Graded by marbling and texture (e.g. USDA Prime, UK R4L)
  • Diamonds – Graded by the 4 Cs: carat, cut, colour, clarity
  • Tea – Graded by leaf size: OP (whole leaf), BOP (broken), Dust (fine)

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.

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