Green Coffee Grading

The Gate Between Farm and Roaster

Green coffee grading is the quality checkpoint that determines whether a lot enters the specialty market or gets downgraded to commodity. It happens at the dry mill after hulling (removing parchment) and before export. Every buyer, exporter, and quality lab uses the same fundamental framework, developed by the Specialty Coffee Association (SCA), to evaluate green coffee on physical attributes before it ever touches a roaster.

I think of the grading table as the final exam. You can do everything right at the farm -- perfect cherry selection, beautiful fermentation, careful drying -- and still fail if the physical grading reveals problems. One full black bean in your 350-gram sample and the lot is disqualified from specialty. That is the reality.

Screen Size

Screen size measures the physical dimensions of green beans using perforated metal screens numbered by 64ths of an inch. The standard screens:

• Screen 18+ (7.14mm) -- large beans, typically from high-altitude Colombian lots
• Screen 16-17 (6.35-6.75mm) -- standard specialty size for Colombian Arabica
• Screen 15 (5.95mm) -- smaller beans, still acceptable but may indicate less development
• Below Screen 14 -- generally excluded from specialty lots

Size matters because uniform screen size ensures even roasting. A mix of large and small beans in the same batch means some will be underdeveloped while others burn. At the dry mill, beans pass through a series of screens to separate by size, and each fraction is evaluated independently.

Our Geisha lots tend to produce larger screen sizes -- predominantly 17-18 -- which is partly genetics and partly the higher altitude where we grow them. The Castillo from our mid-range blocks runs more 15-16, which is perfectly fine for specialty but tells a different story about development.

Defect Counting

The SCA green grading protocol classifies defects into two categories:

Category 1 (Primary) Defects

• Full black -- completely carbonized beans (fermentation defect)
• Full sour -- light brown/yellow, vinegar smell (overfermentation)
• Dried cherry/pod -- unprocessed cherry that passed through the mill
• Large stones/sticks -- foreign material
• Severe insect damage -- broca-damaged beans with multiple bore holes

Category 2 (Secondary) Defects

• Partial black, partial sour -- less severe versions of primary defects
• Broken/chipped -- mechanical damage during hulling
• Quakers -- immature beans that will not develop color during roasting
• Shells -- malformed elephant ears
• Slight insect damage -- single bore hole

Specialty grade requires: zero Category 1 defects and no more than 5 Category 2 defects in a 350-gram sample. This is a strict standard. A single full black bean in your sample disqualifies the entire lot from specialty classification.

I have sat at the grading table and watched a beautiful lot -- one we were sure would score 85+ -- get flagged because of broca damage that our pest management had not caught in time. Those tiny bore holes from the coffee berry borer are hard to spot on the tree, but under the grading lamp they are unmistakable. That is why broca monitoring connects directly to export quality.

Moisture Content and Water Activity

Two measurements that protect the coffee during storage and transport:

• Moisture content -- measured with a moisture meter, target is 10.0-12.0% for export. Below 10%, the coffee tastes flat and faded. Above 12.5%, the coffee risks mold development during ocean transit (a 20-foot container can spend 3-6 weeks at sea in tropical humidity)
• Water activity (Aw) -- measures the available water for microbial growth. Target below 0.60 Aw. This is more predictive of mold risk than moisture content alone

On our farms, we monitor humidity compliance for every lot before it leaves for the dry mill, because once coffee arrives at port with high moisture, the entire container is at risk. I have learned to be paranoid about this. We check moisture with a handheld meter at the bodega, and the trilladora checks it again. If there is any doubt, the lot stays in storage until it reaches the target range.

Export Standards

Beyond SCA grading, Colombian coffee exports must comply with:

• FNC (Federacion Nacional de Cafeteros) quality minimums -- Excelso grade requires Screen 14+ with specific defect limits
• ICO (International Coffee Organization) certificates -- required documentation for international trade
• Phytosanitary certificates -- ICA (Colombian agricultural authority) certifies the coffee is free from quarantine pests
• Importer country requirements -- Japan, the EU, and the US each have specific maximum residue limits (MRLs) for pesticides

The grading table is where science meets commerce. A lot that scores 86 on the cupping table but fails physical grading never reaches the buyer. Every step in the traceability chain is designed to prevent that scenario.

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Green grading is the final gate before your coffee reaches the world. Want to see how we grade and classify our dry mill lots across quality tiers? Join the community at skool.com/particular-3064 for real grading data and export preparation insights.