Green coffee quality
Green Coffee Defects
Quick answer
A defect count converts physical faults found in a defined green sample — commonly 300 g — into weighted "full defect" units. Primary defects such as full black or sour beans count heavily; secondary defects such as broken beans or husk require several occurrences to make one full defect. The weighting tables differ by origin, so counts are not directly comparable between countries.
How defect counting works
A sample of green coffee is drawn to an agreed method, weighed, and picked over by hand on a sorting tray. Every physical fault is identified, categorised and tallied. The tallies are then converted into full defect equivalents using a weighting table, and the resulting figure is what appears in the contract.
The weighting is the part that surprises people. One full black bean is one full defect. Several broken beans are needed to make one. The logic is impact: a full black bean will ruin a cup on its own, a chip will not.
Weighting tables differ by origin
Different origins and different grading systems apply different weightings and different sample sizes. A defect count from one system cannot be compared directly with one from another without knowing both tables. State the system in the contract.
Primary defects
| Defect | Appearance | Likely cause | Cup impact |
|---|---|---|---|
| Full black | Entirely black, often shrivelled | Over-fermentation, dead cherry, ground collection | Rotten, sour, fermented — severe |
| Full sour | Brown to reddish-brown, sometimes waxy | Over-fermentation, over-ripe cherry, contaminated water | Sour, vinegary, onion |
| Dried cherry / pod | Whole or partial dried fruit | Incomplete hulling or pre-cleaning | Ferment, dirty, mouldy |
| Severe insect damage | Multiple bore holes | Coffee berry borer | Dirty, sour; secondary mould risk |
| Foreign matter | Stone, stick, metal | Inadequate cleaning | Physical hazard to mill and roaster |
| Fungus damage | Yellow-brown to reddish discolouration | Mould during drying or storage | Mouldy, musty; food safety concern |
Secondary defects
| Defect | Appearance | Likely cause | Cup impact |
|---|---|---|---|
| Partial black | Less than half the bean blackened | As full black, less advanced | Sour, fermented — moderate |
| Partial sour | Partial brown discolouration | As full sour, less advanced | Sour — moderate |
| Parchment | Bean still in its endocarp | Incomplete hulling | Minimal in cup; roasts unevenly |
| Floater | Pale, low density, often wrinkled | Improper drying or storage | Flat, papery, faded |
| Immature / quaker | Small, wrinkled, silverskin adhering | Under-ripe cherry picked | Fails to brown in roast; grassy, peanutty |
| Withered | Shrivelled, light | Drought stress during development | Thin, grassy |
| Shell | Hollow, ear-shaped fragments | Genetic malformation | Roasts fast, scorches |
| Broken / chipped / cut | Fragments and damaged beans | Aggressive pulping or hulling | Roasts unevenly; more fines |
| Hull / husk | Dried skin fragments | Incomplete cleaning | Ferment, dirty |
| Slight insect damage | One to a few bore holes | Coffee berry borer | Minor unless widespread |
Reading defects diagnostically
A defect profile is a report on the upstream process. The useful question is not only "how many" but "which ones", because the pattern points at where the problem is.
- Blacks and sours dominant → fermentation control, or cherry sitting before processing.
- Quakers and immatures dominant → picking discipline; strip picking or under-ripe deliveries.
- Floaters and faded beans → drying or storage; possibly past crop.
- Broken and cut beans → mechanical settings at the pulper or huller.
- Husk, parchment and foreign matter → dry mill cleaning line, not the farm.
- Fungus damage → drying regime or warehouse conditions; the one category with a food safety dimension.
What a clean defect count does not guarantee
Defect analysis is a physical examination of the green bean. Several of the most damaging faults — particularly phenolic and ferment taints in naturals — leave little or no visible trace. A parcel can pass defect analysis and still cup badly. Physical analysis and cup approval are complementary controls, not alternatives.
Writing a defect tolerance
What the clause needs to state
- Sample size
- Commonly 300 g of green coffee
- Counting system
- Which weighting table applies
- Maximum full defects
- The headline figure
- Category caps
- Separate ceilings for primary defects, foreign matter and stones
- Sampling method
- How the sample is drawn and composited from the parcel
- Point of determination
- Pre-shipment, load port or arrival
- Consequence
- Allowance, rejection or re-determination if exceeded
Defect analysis on your specification
Tell us the counting system and tolerance you work to, and we will report against it on the pre-shipment sample.
See our QC workflowFrequently asked questions
How are coffee defects counted?
What is a quaker?
Can defect counts be compared between origins?
Does a low defect count mean a good cup?
Tell us the coffee you need
Lots can be specified by origin, region, process, grade, screen, moisture, defect tolerance, crop year and packaging. Send what you know and we will confirm what each origin realistically supports.
Keep reading
Related guides
- Green Coffee Grades ExplainedWhat coffee grades actually encode — bean size, density, defect count and preparation — and how the systems used across six East African origins differ.
- Coffee CuppingHow professional coffee cupping works: sample roasting, grind, ratio, water, the break, and the controls that make one table’s results comparable with another’s.
- Dry ProcessingThe mill-side view of dry processing: cherry reception, bed loading, turning regimes, the drying curve and hulling — and the faults that produce phenolic cups.
- Green Coffee MoistureGreen coffee moisture content explained: typical export ranges, why measurement methods disagree, what happens above and below target, and how to write the clause.