How Coffee Beans Are Graded by Size, Altitude, and Process

Ever wonder why some coffees taste bright and complex while others are flat or bitter? Much of it comes down to how the beans were grown, processed, and sorted before they reached your bag. From altitude to processing method, these factors determine not just appearance but cup quality. If you’ve ever stared at a bag of beans wondering what ‘AA’ or ‘washed’ really means, here’s the breakdown.

Coffee beans are graded and categorized by six main factors: processing method (washed or natural), bean shape (flat or peaberry), screen size (mesh number), growing altitude, defect count, and flavor profile. Each element influences taste, consistency, and market value.

What Is a Coffee Bean, Really?

The green coffee bean is the seed inside the fruit of the coffee plant, commonly called the coffee cherry. These cherries turn from green to yellow to red as they ripen. Inside each cherry are usually two flat-sided seeds (flat beans), though occasionally a single round seed (peaberry) forms. The beans you roast and brew come from this fruit after the pulp, mucilage, parchment, and silver skin have been removed.

How Coffee Beans Are Processed: Washed vs. Natural

Coffee beans are processed in one of two main ways, which greatly impact flavor consistency and cleanliness:

• Washed : The coffee cherry is pulped, then fermented and washed to remove all fruit residue before drying. This method results in a cleaner, more uniform cup and is widely used in Central America and Africa.
• Natural : The entire cherry is dried in the sun with the bean inside, then hulled to remove the dried husk. This method is simpler but can yield inconsistent quality due to uneven drying and potential spoilage.

Flat Bean vs. Peaberry: Shape Matters

Most coffee cherries contain two flat beans that sit against each other, creating a flat side on each. Occasionally, a cherry produces a single round bean called a peaberry . Peaberries occur in roughly 5% of all coffee and are often separated during grading. While flavor differences are subtle, peaberries are sometimes considered to have more concentrated taste, though this is not universally agreed upon.

Coffee Bean Size: Screen Size and Mesh Numbers

Coffee beans are sorted by size using vibrating screens with numbered holes (mesh). The larger the mesh number, the smaller the openings—and the bigger the beans that are sorted through them. Sizing helps ensure uniform roasting. Key grades for flat beans include:

• 20–19 mesh: Extra-large
• 18 mesh: Large
• 17 mesh: Medium-large
• 16 mesh: Regular
• 15 mesh: Medium
• 14 mesh: Small
• 13–12 mesh: Extra-small

For peaberries, the sizing is slightly different:

• 13–12 mesh: Large
• 11 mesh: Medium-large
• 10 mesh: Regular
• 9 mesh: Medium
• 8 mesh: Small

These numbers are critical for roasters aiming for even development during roasting.

Altitude: Why Higher Grows Better Beans

Coffee is grown between 200–2500 meters above sea level, but beans grown at higher elevations (1500m+) are widely regarded as superior. Elevation affects growing conditions, bean density, and acidity:

Higher altitudes typically mean slower bean maturation, denser beans, and brighter, more complex acidity—traits sought after in specialty coffee.

Quality Grading: How Defects Define Grade

Coffee quality is assessed by counting physical defects—like black beans, insect damage, or chipped or broken seeds—in a 300g or 350g sample. The fewer defects, the higher the grade. This defect count (called '' in the original) is a key metric in determining export quality, especially for specialty-grade beans.

Flavor Profiles by Origin

Different countries employ their own sensory evaluation methods to test flavor before export. Flavor is influenced by species, processing, altitude, and roast level. Major coffee-producing countries like Brazil, Kenya, Haiti, and Uganda all conduct taste tests to ensure beans meet export standards.

Arabica vs. Robusta vs. Liberica: The Three Main Species

There are three main coffee species traded globally:

• Arabica : Accounts for around two-thirds of global production. Arabica beans are oval, have a sweeter, more complex flavor, and are grown at higher altitudes. They’re preferred in specialty coffee.
• Robusta : Often bitter, less acidic, and with a harsher flavor. Grown at lower altitudes and more resistant to disease, robusta is commonly used in instant and blended coffees.
• Liberica : Rare, with poor cup quality and low yields. Most production is exported to Europe and rarely seen in Japan or specialty markets.

New Crop, Past Crop, and Old Crop: Freshness Factors

Freshness also plays a role in coffee grading and flavor:

• New Crop : Bright greenish beans with sharp acidity and fresh aroma.
• Past Crop :
• Slightly yellow-green beans with mellower acidity.
• Old Crop : Yellowish, dry beans with muted flavors, often used in blends or commercial canned coffee.

From Cherry to Export: Processing Methods in Depth

Before coffee reaches your cup, it undergoes post-harvest processing to remove the fruit and prepare the beans for shipment. There are two primary methods:

• Natural (Dry) Process: The entire coffee cherry is dried in the sun for one to two weeks until it hardens and makes a cracking sound. Then, a machine removes the dried husk, mucilage, and parchment. Common in Brazil, Ethiopia, and Yemen, this method is simple but riskier for contamination and defect inclusion. The resulting cup tends to be lighter and more rustic.
• Washed (Wet) Process: The cherries are sorted and soaked to remove floaters. Then, a depulper removes the skin and pulp. The beans soak in water tanks to ferment and loosen the sticky mucilage, which is then rinsed away. After fermentation (lasting half a day to a full day), beans are washed clean, dried on patios or raised beds, and hulled to remove the parchment. This method, used by Colombia, Guatemala, and Mexico, produces cleaner, brighter beans with fewer defects—but requires careful processing to avoid off-flavors. Properly done, it highlights each bean’s unique characteristics.

Once dried, green coffee beans are packed in jute sacks and shipped worldwide.

Frequently Asked Questions

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

Washed coffee removes the fruit before drying, resulting in a cleaner, more consistent flavor. Natural coffee dries the bean inside the whole cherry, often leading to a fruitier but riskier, inconsistent cup. Washed is preferred for high-quality specialty lots.

What do the mesh numbers mean for coffee bean size?

Mesh numbers refer to the size of the holes in grading screens. Higher numbers (like 18 or 16) mean smaller openings and thus classify smaller beans. Flat beans range from extra-large (20–19 mesh) to extra-small (13–12 mesh), while peaberries use a different scale.

Why are high-altitude coffee beans considered better?

Beans grown at higher altitudes (generally above 1500m) mature more slowly, develop denser beans, and tend to have brighter acidity and more complex flavors—traits prized in specialty coffee.

What are peaberry coffee beans?

Peaberries are rare, round beans that form when only one seed develops inside a coffee cherry instead of two flat beans. They’re often separated and sold separately, sometimes considered to have more concentrated flavor, though this varies.

How are coffee bean defects counted?

Defects like black beans, insect damage, or chipped seeds are counted in a 300–350g sample. The lower the number of defects, the higher the coffee grade and quality, especially for specialty export lots.

What’s the difference between new, past, and old crop coffee?

New crop beans are freshly harvested with bright acidity. Past crop beans are slightly older with mellower flavors. Old crop beans are dry and muted, often used in blends or commercial coffee.