Coffee Bean Specifications and Grades Explained

Ever wondered why some coffee tastes bright and complex while others taste flat or bitter? The difference often starts long before brewing — in how the coffee bean was grown, processed, sorted, and graded. Understanding these factors helps explain why beans from certain regions or farms command higher prices and deliver more nuanced cups.

Coffee bean quality is determined by six key factors: processing method (washed or natural), bean shape (flat or peaberry), screen size, growing altitude, defect count, and sensory evaluation. Each element influences flavor, aroma, 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 a coffee cherry. Most cherries hold two flat-sided seeds (flat beans), but about 5% contain a single round seed (peaberry). These round beans usually develop when only one seed forms inside the cherry. Though flavor differences are subtle, peaberries are often separated for special roasting.

How Coffee Beans Are Processed

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

• Washed (Wet) Process: The coffee cherry is pulped, then fermented to remove the sticky mucilage before washing and drying. This method produces cleaner, more uniform beans with high clarity. Most Colombian, Guatemalan, and Kenyan coffees use washed processing.
• Natural (Dry) Process: The whole cherry is dried in the sun before the beans are removed. This method is simpler but riskier — beans may absorb fruity or fermented flavors, and unripe or defective beans are harder to spot. It’s commonly used in Ethiopia, Yemen, and Brazil.

Coffee Bean Specifications: Size, Shape, and Altitude

Green coffee is sorted and graded by several physical and environmental criteria:

Flat vs Peaberry Beans

Most coffee beans are flat beans — two seeds pressed together with a flat side. Peaberries are rare, round beans formed when only one seed develops. They’re not inherently better, but are often sorted separately.

Bean Size by Screen Size

Coffee beans are graded by passing through metal screens with different hole sizes (measured in 1/64th inches, called “mesh” or “screen number”). Larger beans typically mature more evenly. Common size grades include:

• Flat Beans: 20–19 (very large), 18 (large), 17 (medium-large), 16 (standard), 15 (medium), 14 (small), 13–12 (very small)
• Peaberries: 13–12 (large), 11 (medium-large), 10 (standard), 9 (medium), 8 (small)

Altitude Matters

Higher-grown beans are generally denser and more flavorful due to slower maturation. Coffee-growing altitudes are categorized like this:

Quality and Flavor Grading

Green coffee quality is assessed in two major ways:

• Defect Counting: A sample is inspected, and defects (black beans, insect damage, husks, etc.) are counted. The lower the defect count, the higher the grade. This is a statistical measure of bean cleanliness and uniformity.
• Flavor Testing: Some origins (like Brazil, Haiti, Kenya, and Uganda) conduct sensory evaluations to approve export lots for cup quality.

Arabica vs Robusta vs Liberica

There are three main coffee species:

• Arabica (Coffea arabica): Accounts for around two-thirds of global production. Grows best at higher altitudes, produces oval-shaped beans, and is prized for its acidity, complexity, and aroma. Most specialty coffee is Arabica.
• Robusta (Coffea canephora, aka Canephora): Hardier, grows at lower altitudes, has higher caffeine content, and tastes harsher, more bitter, and less acidic. Often used in instant coffee and espresso blends for crema and body.
• Liberica (Coffea liberica): Rare, with poor yield and flavor. Mostly exported to Europe, rarely seen in Japan or specialty markets.

From Harvest to Export: Processing Methods in Detail

After picking, coffee cherries must be processed to remove all outer layers and reveal the green bean inside. There are two primary methods:

Dry/Natural Process

The harvested cherries are spread out to dry in the sun for one to two weeks until they harden and make a cracking sound. Then a machine removes the dried pulp, parchment, and silver skin. This method is simple but weather-dependent, and more prone to contamination by defective beans. It is common in Brazil, Ethiopia, and Yemen. Resulting beans often have a mild sourness and light body.

Washed/Wet Process

The cherries are first sorted in water tanks — unripe or defective cherries float and are discarded. Then a depulper removes the skin and pulp. The beans soak in water tanks where natural fermentation breaks down the mucilage (sticky layer). After 12–24 hours, the beans are washed clean, dried on patios or beds for several days, and then hulled to remove the parchment. The result is cleaner-tasting beans with high clarity and fewer defects. Used widely in Colombia, Guatemala, and Mexico. If fermentation isn’t controlled, unwanted sour or funky flavors can develop.

After processing, green beans are sorted by density and size, bagged in jute sacks, and shipped worldwide. Proper handling ensures they arrive in roasters’ hands ready to shine.

New Crop, Past Crop, and Old Crop

Coffee is also categorized by harvest age:

• New Crop: Recently harvested, bright acidity, vivid green color, pronounced aroma.
• Past Crop:
• Slightly aged, yellowish-green, milder acidity, smoother flavor.
• Old Crop: Dried-out, yellow beans, flat acidity, used mostly in blends or commercial canned coffee.

Frequently Asked Questions

What are the main differences between washed and natural processed coffee beans?

Washed (wet) process beans are cleaned right after harvest using water and fermentation to remove the fruit layer, resulting in a cleaner, brighter cup with higher clarity. Natural (dry) process beans are dried with the fruit still on, creating more fruity, fermented, or full-bodied flavors but with less consistency and more risk of defects.

How is coffee bean size measured and why does it matter?

Coffee bean size is measured using screen sieves with holes sized in 1/64-inch increments. Common designations include No. 18 (large) to No. 14 (small) for flat beans, and No. 10 to No. 8 for peaberries. Larger beans often mature more evenly and are associated with higher elevations and better quality.

Does altitude really affect coffee flavor?

Yes. Coffee grown at higher altitudes (typically 1,200 meters and above) tends to be denser, slower to ripen, and develops more complex sugars and acids. These beans usually have brighter acidity, more nuanced flavors, and are considered higher quality.

What’s the difference between Arabica and Robusta coffee beans?

Arabica beans make up about two-thirds of global production and are valued for their acidity, aroma, and complex flavors. They grow best at higher altitudes. Robusta beans are hardier, contain more caffeine, taste harsher and more bitter, and are often used in espresso blends and instant coffee for their strong body and crema.

How are coffee bean defects counted and why do they matter?

Defects are non-conforming beans such as black, sour, broken, or insect-damaged ones. A sample is inspected, and the number of defects is counted. A lower defect count means higher bean quality and a cleaner cup. This is a key part of green coffee grading.

What does 'new crop' coffee mean?

New crop refers to coffee beans recently harvested and processed. They typically have vibrant acidity, fresh aromas, and bright green color. Over time, beans lose moisture and freshness, becoming 'past crop' or 'old crop' with more muted flavors.