Kenya AA, AB, PB explained: a buyer's guide to the grades

If you have ever picked up a bag of Kenyan coffee, you have seen the letters. AA. AB. PB. Sometimes TT, T, or C in smaller print. They look like an academic grading scheme. They are not. They tell you almost nothing about whether the coffee will taste good, and a lot about whether the coffee will roast evenly. Both of those facts are important. Most buyers know neither.

Here is the full explainer.

What the grades actually are

Kenyan coffee is graded after milling, by passing the green beans over a series of screens with progressively smaller holes. The screens sort the beans by size. The bigger the bean, the higher the grade. That is it. Grade is a physical sorting category, not a taste category. A small bean is not a worse bean. It is a smaller bean.

There is a quality correlation, but it is loose, and it is downstream of the sorting. We will get to that in a moment.

The official Kenyan grade ladder, from largest to smallest:

• AA: screen 17/18 and above (roughly 7.2mm and up). The largest beans in the lot.
• AB: a combined grade of screens 15, 16, and 17. The medium and upper-medium beans, blended together.
• PB (peaberry): a separate category, not based on size. Peaberries form when a coffee cherry produces a single round bean instead of the usual two flat beans. They are roundish, smaller than AA, and sorted out separately at the mill.
• C: screens below 15. Smaller beans.
• TT: lighter-density beans that float during density sorting, regardless of size. Often less developed.
• T: the smallest screens and the broken or chipped beans.
• MH / ML: heavy and light mbuni, which is the term for unwashed (dry-processed) Kenyan coffee. A separate category entirely.

A single farm's harvest will produce all of these grades. A typical washed Kenyan lot might split 25-35% AA, 35-45% AB, 5-10% PB, 10-15% C, and the rest in lower grades. The exact split depends on the cultivars, the season, and the picking discipline.

So is AA the best?

It is the most expensive at the auction. It is the most marketed abroad. It is not necessarily the best in the cup.

Here is the loose quality correlation. Larger beans had access to more nutrients and more time on the tree before being picked, on average. They tend to have slightly more density and slightly more development. They also roast more evenly because uniform size means uniform heat exposure. Roasters love AA for that reason. Their drum behaves more predictably.

But the differences in cup quality between a great AA, a great AB, and a great PB from the same farm are often smaller than the differences between a good and a great roast of any one of them. I have served AB lots in competition that scored higher than AA lots from the same washing station. The judges did not care about the screen size. They cared about the cup.

The honest hierarchy for a serious buyer:

1. The cooperative or estate matters most.
2. The harvest year matters next.
3. The processing matters next.
4. The cultivar matters next.
5. The grade matters last.

If a bag tells you AA and nothing else, the bag is bluffing.

What about peaberry (PB)?

Peaberries are the unicorn of Kenyan grading. They are the round single-bean version of a coffee cherry, formed when only one of the two ovules in the cherry develops. About 5-10% of any harvest comes out as peaberry.

Two things to know:

They roast differently. Round beans transfer heat more evenly than flat beans. A skilled roaster can pull out a sweetness and clarity in a PB that is hard to get from the same lot's AA. This is why a lot of competition baristas, myself included, often choose PB for specific routines.

They are not automatically better. A bad PB lot from a poorly managed estate is a bad coffee regardless of the round shape. The same hierarchy applies. The farm matters more than the geometry of the bean.

What about the lower grades?

C, TT, and T grades are typically sold for local consumption, instant coffee, or as filler in commodity blends. They are not, on average, worth seeking out as a specialty buyer. But occasionally a great washing station will produce a stunning C lot that just happened to come from younger trees or smaller cultivars, and an attentive buyer will catch it. It is rare. Default to AA, AB, or PB unless you have a reason.

The grades TT and T are particularly worth avoiding for specialty drinking. They include lighter and broken beans that roast unevenly and tend to taste flat or papery in the cup. They have a place in the commodity chain. They do not belong in a premium bag.

How to use the grade when you buy

Practical buying rules:

• AA is your default for a clean, structured, classic Kenyan washed cup. Buy AA when you want the textbook Kenya experience.
• AB is the value play. The cup is often 90-95% as good as the AA from the same lot, at 60-75% of the price. Buy AB when you want quality without paying the AA premium.
• PB is the curiosity play. Buy a small bag of peaberry from a producer you already trust, and brew it side by side with their AA. You will learn more about Kenyan coffee from that one comparison than from reading any guide.

In all three cases, the grade alone is not enough. Always ask for the harvest year, the cooperative or estate, the cultivar, and the roast date. Without those, the grade is theatre.

A final word on commodity Kenyan

There is a lot of coffee in Kenya, and most of it never makes it into the specialty conversation. The commodity portion of the country's harvest goes into instant coffee, into supermarket blends, into the global undifferentiated brown-liquid economy. It is not bad coffee. It is just generic coffee.

If you are reading this, you are probably looking for the other Kenya. The cooperative-named, harvest-dated, recently roasted, grade-labelled, processing-disclosed Kenya. That coffee exists. It costs more. It is worth it. And it is one of the most rewarding origins you will ever drink.

Pick up a bag from a small roaster who can answer the five questions. Brew it twice a day for a week. The grade on the bag will be the last thing you remember about it.

Martin