Green coffee grading is the standardized process of evaluating unroasted coffee beans for quality, size, and defects. For buyers, exporters, and roasters, understanding grading systems is essential for accurate quality assessment, fair pricing, and successful coffee trading.
Why Green Coffee Grading Matters
Quality Communication
Grading provides a common language for quality:
- Buyers understand what they’re purchasing
- Sellers accurately represent their coffee
- Prices reflect actual quality levels
- Disputes are minimized through clear standards
Value Determination
Grades directly impact coffee pricing:
- Higher grades command premium prices
- Defect counts affect value calculations
- Size consistency influences roasting uniformity
- Screen size determines market positioning
Key Grading Parameters
1. Screen Size
Coffee beans are sorted by size using screens with specific hole diameters:
| Screen Size | Hole Diameter | Common Grade Name |
|---|---|---|
| 20 | 8.0 mm | Very Large |
| 18 | 7.1 mm | Large (AA) |
| 17 | 6.7 mm | Bold |
| 16 | 6.3 mm | Medium (AB) |
| 15 | 6.0 mm | Standard |
| 14 | 5.6 mm | Small |
| 13 | 5.2 mm | Peaberry (PB) |
Why Size Matters:
- Uniform size ensures even roasting
- Larger beans often (not always) indicate better quality
- Market preferences vary by region and use
2. Defect Count
Physical defects are counted and categorized:
Primary (Full) Defects:
- Full black beans
- Full sour beans
- Dried cherry/pod
- Large stones
- Large sticks
Secondary (Partial) Defects:
- Partial black/sour
- Broken beans
- Insect damage
- Shells/husks
- Immature/quakers
Defect Calculation:
Different defects carry different weights. For example:
- 1 full black = 1 full defect
- 5 broken beans = 1 full defect
- 10 insect-damaged beans = 1 full defect
3. Color and Appearance
Visual assessment evaluates:
- Color uniformity: Consistent green, blue-green, or yellowish tones
- Processing indicators: Washed beans typically appear cleaner
- Age signs: Fresh coffee shows brighter coloration
- Foreign matter: Non-coffee particles are defects
4. Moisture Content
Ideal moisture levels for storage stability:
- Target range: 10-12%
- Too high (>12.5%): Risk of mold and fermentation
- Too low (<9%): Accelerated aging and flavor loss
5. Water Activity
A more precise moisture indicator:
- Target range: 0.55-0.65 aw
- Predicts shelf stability better than moisture content alone
- Increasingly used in specialty coffee evaluation
Regional Grading Systems
East African Grading (Uganda, Kenya, Tanzania)
Ugandan System:
- Screen 18: Large beans, premium grade
- Screen 15: Standard export grade
- Bugisu AA: Top Arabica grade from Mt. Elgon
- Drugar: Standard Robusta grade
Kenyan System:
- AA: Screen 17-18, premium grade
- AB: Screen 15-16, good quality
- PB: Peaberry, sought after for unique flavor
- C: Screen 14-15, lower grade
Ethiopian Grading
Ethiopian Coffee and Tea Authority grades:
- Grade 1: 0-3 defects per 300g (specialty)
- Grade 2: 4-12 defects per 300g (specialty)
- Grade 3: 13-27 defects per 300g (commercial)
- Grades 4-5: Higher defect counts
Brazilian/Colombian Systems
Screen-based with defect counts:
- Supremo (Colombia): Screen 17+
- Excelso (Colombia): Screen 14-16
- NY 2 (Brazil): Max 4 defects per 300g
Specialty Coffee Grading (SCA Standards)
The Specialty Coffee Association defines specialty green coffee as:
Green Grading Requirements
Sample size: 350 grams
Defect tolerance: Maximum 5 full defects
No primary defects (quakers, full black/sour) allowed
Moisture: 10-12%
Cupping score: 80+ points
Specialty Classifications
| Classification | Defect Count | Cupping Score |
|---|---|---|
| Specialty Grade | 0-5 | 80+ |
| Premium Grade | 6-8 | 75-79 |
| Exchange Grade | 9-23 | Below 75 |
Best Practices for Green Coffee Evaluation
1. Sample Preparation
- Use representative samples from the lot
- Sample 350g minimum for accurate assessment
- Ensure proper sample storage and handling
2. Visual Inspection
- Work on a well-lit, neutral-colored surface
- Spread beans evenly for thorough examination
- Use magnification for detailed defect identification
3. Defect Identification
- Sort defects into categories
- Count and weigh according to standard equivalents
- Document findings systematically
4. Size Analysis
- Use calibrated screens
- Screen in size order (largest to smallest)
- Calculate percentages for each screen size
5. Moisture Testing
- Use calibrated moisture meters
- Test multiple points in the sample
- Record conditions at time of testing
Common Grading Challenges
Inconsistent Standards
Different origins use different systems:
- Convert between systems using reference charts
- Request specific grade definitions from suppliers
- Develop internal standards for consistent buying
Subjective Assessments
Some evaluations are judgment-based:
- Train graders consistently
- Calibrate teams regularly
- Use multiple graders for important decisions
Sample Representativeness
Samples may not reflect full lots:
- Request samples from multiple bag positions
- Verify sample handling procedures
- Re-evaluate upon arrival if concerns exist
Technology in Grading
Modern tools enhance traditional grading:
- Electronic color sorters: Automated defect removal
- Optical graders: Consistent size and color analysis
- Near-infrared spectroscopy: Moisture and composition analysis
- Machine learning: Automated defect detection
Conclusion
Green coffee grading combines standardized methods with trained judgment to evaluate coffee quality accurately. Understanding grading systems enables better buying decisions, fairer pricing, and clearer communication throughout the coffee supply chain. Whether sourcing Ugandan Robusta or Ethiopian Arabica, proper grading ensures quality expectations are met.
Keywords: green coffee grading, coffee bean classification, coffee defects, coffee screen size, SCA grading standards, specialty coffee grading, coffee quality assessment
Meta Description: Master green coffee grading with this comprehensive guide. Learn about screen sizes, defect counts, regional grading systems, and SCA specialty standards for accurate coffee quality evaluation.
