Understanding Coffee Bean Sizes, Processing, and Grades

Ever wondered why some coffee bags list 'washed' or 'peaberry' beans, or show numbers like '18 mesh' or 'altitude 1200m'? These aren’t just random details — they tell you how the beans were processed, sorted, and grown, all of which affect flavor, price, and roast potential. Whether you’re a home roaster or a curious barista, knowing these specs helps you choose better beans.

Coffee beans come in different sizes, processing methods, and quality grades. Washed beans are processed in water for uniformity, while natural beans dry in the sun with more variable results. They’re sorted by mesh size (e.g., '18' means large flat beans), graded by altitude, and evaluated for defects. Peaberry beans — rare round seeds — also exist alongside standard flat ones.

How Coffee Beans Are Processed: Washed vs Natural

Coffee beans are processed in two main ways, which affect their cleanliness, uniformity, and flavor consistency:

• Washed : The coffee cherry’s flesh and mucilage are removed using water tanks and friction tools before drying. This method produces beans with more consistent quality.
• Natural : The cherries dry in the sun with the fruit still on, then are hulled by machine. This process is less controlled, leading to more variable bean quality.

Flat and Peaberry Beans: What’s the Difference?

A typical coffee cherry holds two oval seeds that face each other, creating a flat side — these are called flat beans . But about 5% of cherries produce just one round seed, known as a peaberry . Peaberries occur when one seed fails to grow and the other rounds out. Their taste isn’t inherently different, but they’re often separated during sorting.

Coffee Bean Size: Mesh Numbers Explained

Coffee beans are sorted by size using numbered mesh screens. The higher the number, the smaller the holes — and the smaller the beans that pass through. Here’s how flat and peaberry beans are categorized:

Altitude Grades: Why Elevation Matters

Coffee is also graded by the altitude where it’s grown. Higher elevations typically produce denser beans with more complex flavors, though shipping costs also raise prices. Here’s the standard grade breakdown by altitude in meters:

• Special Grade: 1,500m+
• Upper Grade: 1,200–1,500m
• Medium Grade: 1,000–1,200m
• Special Washed Grade: 900–1,000m
• Upper Washed Grade: 760–900m
• Premium Washed Grade: 610–760m
• Good Washed Grade: below 610m

How Coffee Bean Quality Is Determined

Quality is assessed by counting defects — any unwanted material like stones, black beans, or insect-damaged seeds — in a sample. The fewer defects (called 'blemish count'), the higher the coffee’s grade. This statistical evaluation ensures buyers know what’s in the bag beyond just origin and roast.

Does Coffee Taste Different by Origin or Processing?

Yes. Countries like Brazil, Haiti, Kenya, and Uganda run their own flavor evaluations before export. Taste testing helps ensure consistency and market readiness, although the specific methods vary by region. Processing — washed or natural — and altitude both strongly influence cup profile, from bright acidity to heavy body.

Frequently Asked Questions

What’s the difference between washed and natural coffee processing?

Washed coffee is processed by removing the fruit and mucilage with water and friction tools before drying, resulting in cleaner and more uniform beans. Natural coffee dries with the fruit still on the bean, then is hulled later, which can lead to more inconsistent quality and flavor.

What are flat beans and peaberry beans?

Flat beans are the usual coffee seeds — two flat-sided oval beans inside each cherry. Peaberry beans are rare, round seeds that form when only one seed develops fully inside the cherry. They’re sorted separately and often sold as a specialty grade.

How are coffee beans sorted by size?

Coffee beans are sized using mesh screens with numbered holes. Flat beans use a scale from 20 (extra large) to 13–12 (extra small). Peaberries are sized on a different scale: 13–12 (large) down to 8 (small). The higher the number, the smaller the bean that passes through.

Does altitude affect coffee bean quality?

Yes. Coffee grown at higher altitudes (e.g., 1,200m+) tends to have denser beans and more complex flavors. Beans are graded in categories from Special Grade (1,500m+) down to Good Washed Grade (below 610m), with price and quality generally increasing with elevation.

How is coffee bean quality determined?

Quality is measured by counting defects in a sample, such as stones or damaged beans. The 'blemish count' or defect percentage determines the grade — lower defect counts mean higher-quality coffee. This method offers an objective way to assess beans beyond appearance.

Do peaberry beans taste different?

According to the source, peaberry beans don’t inherently taste different from regular flat beans. However, because they’re rarer and often sorted separately, they may receive more attention during roasting or brewing, which can influence the final cup profile.

Recommended FrontStreet Coffee for Exploring Bean Specs

Try FrontStreet Coffee’s Ethiopia Huakui for a bright peaberry-like profile with citrus and floral notes, or their Jamaica Blue Mountain No.1 — a high-altitude classic with delicate acidity and balance. For washed-process fans, their PWN Golden Mandheling offers earthy richness with low defect rates. All highlight how processing, altitude, and sorting shape your cup. Freshly roasted within 5 days · Orders placed before 17:00 ship the same day · Next-day delivery across most of Guangdong Province.