Quality Control in Processing

The Quality Control Chain

Quality control (QC) in coffee is a multi-stage process that begins at the wet mill and continues through dry milling, export grading, import evaluation, and roastery intake. At each stage, trained professionals use standardized tools and protocols to assess, grade, and either approve or reject a lot. Understanding these systems helps you appreciate why some coffees cost $5 per kilogram and others cost $50.

Physical Defect Analysis

The foundation of green coffee grading is defect counting. The SCA Green Coffee Grading Protocol defines two categories:

Category 1 (primary) defects — any of these disqualifies a lot from specialty classification: - Full black bean - Full sour bean - Dried cherry/pod - Fungus-damaged bean - Foreign matter (stones, sticks) - Severe insect damage

Category 2 (secondary) defects — these are counted and allowed in limited quantities: - Partial black/sour beans - Broken/chipped/cut beans - Shells (elephant ears) - Floaters (lightweight beans) - Immature/unripe beans (quakers) - Hulls, husks

The grading protocol: 1. Take a 350-gram sample from a representative portion of the lot 2. Hand-sort all defective beans onto a separate tray 3. Count and categorize each defect using the SCA defect equivalence chart 4. Specialty grade requires: zero Category 1 defects and fewer than 5 full Category 2 defect equivalents

Moisture Measurement

Every QC lab requires a calibrated moisture meter to verify that green beans fall within the 10–12% target range. Common instruments:

Moisture readings are taken at multiple points in the lot — top, middle, and bottom of bags — to detect inconsistency. A single bag reading 13.5% in a lot that averages 11% may indicate water damage or improper drying.

Screen Size (Sizing)

Beans are sifted through screens with numbered round holes to determine size distribution. Screen sizes are measured in 64ths of an inch:

• Screen 18+ (7.14mm+) — large, premium grade
• Screen 16 (6.35mm) — standard specialty
• Screen 14 (5.56mm) — smaller, but acceptable
• Below 14 — typically commercial grade

Uniform screen size is important because it ensures even roasting — mixed sizes roast at different rates, producing inconsistent extraction.

Density and Color

Density correlates with altitude and affects roast behavior. High-density beans (grown above 1,400m) require more heat energy to develop. Labs measure density using displacement methods or instruments like the Sinar AP-6060 or Lighttells.

Color is measured with a colorimeter (commonly Agtron or Lighttells) on both green and roasted samples. Green bean color indicates freshness and processing type: - Fresh washed: blue-green - Fresh natural: yellow-green - Aged/past crop: brown-yellow

Sample Roasting

Before a lot is purchased or approved, it is sample roasted — a small batch (100–150 grams) roasted on a dedicated sample roaster to a standardized light-medium profile. The SCA protocol specifies:

• Roast time: 8–12 minutes
• Target color: Agtron 58±1 (whole bean) / 63±1 (ground)
• Cooling: maximum 3 minutes
• Resting: minimum 8 hours before cupping

Common sample roasters include the Ikawa Pro (hot air, digitally profiled), Probatino, and the Roest (Norwegian design with automated profiles). Consistency between sample roasts is critical — the goal is to evaluate the green coffee, not the roast.

Cupping Protocol

Professional cupping follows the SCA Cupping Protocol, designed to evaluate coffee under standardized conditions:

Preparation: - Ratio: 8.25 grams per 150 ml water - Grind: medium-coarse (passing 70–75% through a 20-mesh sieve) - Water: 93°C, freshly heated, TDS 75–250 ppm - Minimum 5 cups per sample to assess uniformity

Evaluation sequence: 1. Fragrance (0:00) — smell the dry grounds 2. Crust break (4:00) — break the crust with a spoon, evaluate wet aroma 3. Skim (6:00) — remove floating grounds 4. Slurp (8:00–12:00) — aspirate coffee from the spoon, evaluating flavor, acidity, body, balance 5. Cool-down (12:00+) — evaluate as temperature drops; defects often become more apparent as coffee cools

Scoring: Each attribute is scored on a 6–10 point scale. The total (minus defect deductions) produces the final score out of 100. Specialty grade requires 80+.

Defect Detection in the Cup