Coffee Bean Size, Grade, and Processing Basics

If you’ve ever wondered why some coffees cost more or taste brighter, the answer often lies in how the beans were grown, processed, and sorted—not just the roast. From bean shape to screen size and altitude, these factors define a coffee’s profile before it even reaches your cup. This guide breaks down the essentials.

In short: Washed beans are processed uniformly in water, producing consistent quality, while natural beans dry in the sun with fruit attached, leading to more variable results. Flat beans are the standard oval shape; peaberries are round and occur when one seed in the coffee cherry fails to split. Screens numbered 15–18 (mesh) typically mark specialty-grade sizes.

How Coffee Beans Are Processed

Coffee cherries can be processed in two main ways. Washed (or wet) process involves removing the fruit and mucilage by soaking and friction in water tanks, resulting in a cleaner, more uniform cup. Natural (or dry) process dries the whole cherry in the sun before hulling, which can create richer flavors but often with less consistency. Washed beans are generally more predictable in profile.

Flat vs. Peaberry Coffee Beans

A typical coffee cherry holds two flat-sided seeds (flat beans), but about 5% contain a single round seed—the peaberry . This occurs when one seed doesn’t separate during development. Though the shape differs, peaberries don’t inherently taste different. Flat beans have the usual oval, flat-faced form, while peaberries are entirely rounded. Both can appear in any origin or process.

Coffee Bean Size by Screen Mesh

Coffee beans are sorted and graded by size using numbered screens (mesh). The larger the mesh number, the smaller the holes—and the smaller the beans that pass through. Here’s how it breaks down:

Altitude and Coffee Grade

Coffee is also graded by the elevation where it’s grown. Higher altitudes generally slow growth, producing denser beans with more complex flavors. Grades are assigned based on minimum altitude in meters:

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

How Coffee Quality Is Determined

Quality is assessed by counting defects—foreign matter, insect damage, broken or immature beans—in a sample. The fewer the defects (called ), the higher the grade. This statistical method ensures consistency and helps roasters select beans with the best potential cup quality.

Does Taste Vary by Country?

Yes. Countries like Brazil, Haiti, Kenya, and Ethiopia conduct their own flavor evaluations before export. These taste tests help ensure that only coffees meeting certain sensory standards reach global markets. While methods vary by origin, they aim to maintain cup quality and profile integrity.

Frequently Asked Questions

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

Washed coffee is processed by removing the coffee cherry’s skin and pulp using water and friction, which results in a cleaner, more uniform flavor. Natural coffee dries the whole cherry in the sun before hulling, often producing fruitier but less consistent flavors due to variable drying conditions.

What are peaberry coffee beans?

Peaberries are single, round coffee beans that form when one seed in a coffee cherry does not split during development. They make up about 5% of all coffee and are not a separate variety, just a different shape. They can occur in any coffee origin and are not inherently better or worse in taste.

How are coffee beans sized?

Coffee beans are sized using screen meshes with numbers indicating hole size. Higher mesh numbers mean smaller holes and smaller beans. For flat beans, grades range from Extra Large (mesh 20–19) to Extra Small (mesh 13–12). For peaberries, grades include Large (mesh 13–12) down to Small (mesh 8).

Does altitude affect coffee quality?

Yes. Generally, coffee grown at higher altitudes (1,200 m and above) is denser and develops more complex flavors due to slower maturation. Grades such as (1,500+ m) and (1,200–1,500 m) indicate higher quality due to elevation. Lower-altitude beans (below 610 m) are considered lower grade.

How is coffee bean quality determined?

Quality is measured by counting defects in a sample—the less defective beans (like broken, black, or immature ones), the higher the grade. This defect count, or , is a key metric in determining the overall quality and market value of green coffee beans.

Recommended FrontStreet Beans for Size & Grade Insights

Try FrontStreet’s Ethiopia Yirgacheffe for a bright, high-altitude washed coffee (typically grade 15–16 screen size), showcasing the clarity of high-grown washed beans. Their Colombia Huila offers balanced medium-large beans (screen 16–17) grown at 1,400–1,800 m, ideal for seeing how elevation impacts cup profile. For peaberry enthusiasts, their Tanzania Peaberry highlights the rounded bean type with intense citrus and floral notes, usually graded in the upper peaberry screen range. All are single origins with transparent processing—reflecting the very factors discussed here. Freshly roasted within 5 days · Orders placed before 17:00 ship the same day · Next-day delivery across most of Guangdong Province.