Green Coffee Grading — SCA Defect Classification and Moisture Standards
SCA Grade 1 green coffee: 0 primary defects, ≤5 secondary defects per 350g sample, screen size 15+, moisture 10–12%. Primary defects include full black, full sour, pod/cherry, large stone, large stick.
| Measure | Value | Unit | Notes |
|---|---|---|---|
| Grade 1 primary defects | 0 | defects per 350g | Any primary defect disqualifies Grade 1 status |
| Grade 1 secondary defects | ≤5 | defects per 350g | Secondary defects counted on equivalency scale |
| Grade 2 primary defects | ≤3 | defects per 350g | |
| Grade 2 secondary defects | ≤5 | defects per 350g | |
| Moisture content target | 10–12 | % | Below 10% causes brittleness; above 12% risks mold |
| Minimum screen size (Grade 1) | 15+ | screen (1/64 inch units) | Screen 15 = 15/64 inch (≈6mm) — filters out undersized beans |
| Sample weight for grading | 350 | g | SCA standard evaluation sample size |
Green coffee grading provides a standardized language for the commodity and specialty coffee trades to evaluate raw beans before roasting. The SCA (Specialty Coffee Association) grading system, developed from earlier Brazilian and New York exchange standards, classifies green coffee by defect count, moisture content, and screen size.
SCA Grade Definitions
| Grade | Primary Defects | Secondary Defects | Cup Quality |
|---|---|---|---|
| Grade 1 (Specialty) | 0 | ≤5 | Must score ≥80 on cupping scale |
| Grade 2 (Premium) | 0 | ≤8 | Cup quality demonstrated |
| Grade 3 (Exchange) | ≤9 (combined) | — | No cup defects allowed |
| Grade 4 (Standard) | 10–23 | — | — |
| Grade 5 (Off-Grade) | 24+ | — | Below commercial standard |
All grading is performed on a 350g sample. The SCA Grade 1 classification additionally requires that the coffee cups without defects — a green grade alone is insufficient for Specialty designation.
Primary Defect Classification
| Defect | Cause | Cup Impact |
|---|---|---|
| Full black bean | Overripe on tree or on ground | Fermented, phenolic off-flavor |
| Full sour bean | Bacterial fermentation during processing | Vinegar, acetic acid off-flavor |
| Dried pod / cherry | Unhulled fruit passes through processing | Fermented, woody off-flavor |
| Large stone (>5g equivalent) | Foreign matter contamination | Equipment damage risk |
| Large stick (>5g equivalent) | Foreign matter contamination | Equipment damage risk |
Each primary defect found in the 350g sample counts as one full defect unit. A single primary defect disqualifies Grade 1 status.
Secondary Defect Equivalencies
Secondary defects are counted on an equivalency scale where a set number equals one primary defect:
| Secondary Defect | Equivalent Count |
|---|---|
| Partial black bean | 3 = 1 primary defect |
| Partial sour bean | 3 = 1 primary defect |
| Parchment bean | 5 = 1 primary defect |
| Floater bean | 5 = 1 primary defect |
| Immature/unripe bean | 5 = 1 primary defect |
| Withered bean | 5 = 1 primary defect |
| Shell/quaker | 5 = 1 primary defect |
| Small stone (<5g) | 2 = 1 primary defect |
| Small stick (<5g) | 2 = 1 primary defect |
Moisture Content Standards
Green coffee moisture content must fall within 10–12% (measured by weight) for SCA Grade 1. Moisture affects:
- Storage stability: Above 12%, mold and mycotoxin risk increases
- Roast behavior: Below 10%, brittle beans may fracture or roast unevenly
- Weight accuracy: Higher moisture = heavier weight; buyers test moisture before purchase
- Shelf life: Properly dried coffee (10–12%) stored in GrainPro bags retains quality for 12–18 months
Screen Size and Density
Screen size 15 is the minimum for Grade 1, but screen size alone is not a complete quality proxy. High-altitude Arabica from dense growing regions (Ethiopia Yirgacheffe, Colombia Huila) often grades screen 17–20. However, some exceptional varieties (Gesha, Pacamara) grow large even at moderate altitudes, while high-altitude Robusta may be small-screened. Density testing (using a flotation tank or pneumatic separator) provides additional quality data beyond screen size.
Related Pages
Sources
- SCA Green Coffee Grading Handbook
- SCA Green Coffee Classification System
- ICO Coffee Report — Quality Standards
- USDA Coffee Quality Analysis
Frequently Asked Questions
What is the difference between a primary and secondary defect?
Primary defects are severe quality failures that each count as one full defect unit: full black bean, full sour bean, dried cherry/pod, large stone, large stick, large clod. Secondary defects are less severe but still affect cup quality — partial black, partial sour, parchment, floater, immature/unripe, withered, shell, small stone, small stick, small clod. Multiple secondary defects are required to equal one primary defect equivalent.
Why does moisture content matter so much for green coffee?
Moisture content at 10–12% represents an equilibrium with stable storage conditions. Below 10%, the bean's cellular structure becomes brittle and the roast behaves erratically — beans may crack prematurely or roast unevenly. Above 12%, the risk of mold growth and mycotoxin contamination (particularly ochratoxin A) increases substantially. Moisture also affects weight-based commodity pricing — buyers test moisture before purchase.
What does screen size 15 actually mean in physical dimensions?
Screen sizes are measured in units of 1/64 inch. Screen 15 = 15/64 inch = approximately 5.95mm. This is the minimum hole size through which a qualifying bean must not pass — beans that fit through are rejected as undersized. Larger screen sizes (17–20) are often associated with premium Specialty grade lots from high-altitude origins where beans develop more slowly and achieve greater density and size.
Does SCA grading predict cup quality directly?
Green coffee grading primarily screens for defects that cause off-flavors — fermentation defects (sour), overripe beans (black), foreign matter (stone, stick). It correlates with minimum quality thresholds but does not predict the flavor complexity, sweetness, or terroir expression that determines a coffee's cupping score. A Grade 1 coffee can score anywhere from 80 to 94+ on the SCA cupping scale depending on origin, processing, and roast.