What are primary defects in green coffee?
Primary defects in green coffee are the most serious imperfections identified in a batch of green beans before roasting. The SCA defines five main categories: full black bean, full sour bean, dried cherry, foreign matter (husks, foreign seeds), and fungus-damaged beans. Each defect corresponds to a severe sensory impact in the cup.
The SCA Arabica green coffee defect classification distinguishes primary from secondary defects based on their cup impact. A single full black bean in a 350 g sample constitutes one complete defect — one bean is enough to potentially disqualify a lot. Each type of primary defect has a specific origin and sensory profile.
The full black bean results from harvesting overripe cherries that have fallen to the ground, or from Erwinia bacterial infection. In the cup it generates phenolic, medicinal, or burnt leather flavours. The full sour bean comes from excessively long uncontrolled fermentation — the bean has fully fermented before or during depulping. It produces a pronounced vinegar taste in the cup, sometimes with an alcoholic note. Dried cherries are whole cherries that the depulping process failed to remove; during roasting they generate an over-fermented cherry flavour and can create uneven burning spots in the drum. Foreign matter (stones, twigs, seeds of other species) has no direct aromatic impact but poses a mechanical risk to roasting and grinding equipment.
Fungal damage (green beans with visible moulds or mycotoxins) is arguably the most serious defect — not in terms of taste but food safety: certain moulds produce ochratoxin A, regulated by the European Union since 2005 in roasted coffee (maximum 10 µg/kg). A fact worth knowing: ochratoxin A is heat-stable — it does not break down during roasting. This is why specialty coffee insists on impeccable drying of green beans to a residual moisture of 10-12 %: below this threshold, moulds cannot develop.
The 5 SCA primary defects in green Arabica coffee
| Defect | Main cause | Sensory impact in cup | SCA defect equivalence |
|---|---|---|---|
| Full black bean | Late harvest, fallen to ground, Erwinia | Phenolic, medicinal, burnt leather | 1 bean = 1 full defect |
| Full sour bean | Uncontrolled prolonged fermentation | Vinegar, alcohol, acetic acid | 1 bean = 1 full defect |
| Dried cherry | Insufficient depulping | Over-fermented, harsh cherry, uneven burning | 1 cherry = 1 full defect |
| Foreign matter | Insufficient sorting, contamination | No direct taste impact | 1 object = 1 full defect |
| Fungal damage | Excessive moisture, storage failure | Musty, earthy, mycotoxins | 1 bean = 1 full defect |
Sorting the Field: How Green Coffee Defects Define Quality Before the Roast
The most consequential quality decisions in coffee happen not at the roaster or the café but at the sorting table in a processing station, where green coffee is evaluated for physical defects that will harm or destroy cup quality long before any heat is applied. The SCA green coffee classification system identifies two categories of defects: Category 1 defects (full blacks, full sours, pods/husks, large stones or sticks, mould-damaged beans) which are disqualifying in specialty coffee — even one of certain types per 350-gram sample fails the lot — and Category 2 defects (partial blacks, partial sours, broken/chipped beans, shells, small stones or sticks, water damage) which are tolerable only in strictly limited numbers.
Understanding why specific defects matter illuminates the whole logic of green coffee quality control. Full black beans — beans that have turned entirely black, indicating complete fermentation or cellular breakdown — produce a harsh, rotting, sour note that contaminates every cup containing even one of them. This is why specialty standard requires zero full blacks per 350g sample. Full sours — beans with yellow or brown interiors from internal fermentation — produce an acetic, vinegary note similarly disruptive to cup quality. Insect damage allows mould to enter the bean's interior through entry holes bored by the Coffee Berry Borer (CBB), the most economically damaging pest in coffee globally, producing earthy and musty defect compounds that roasting cannot neutralize.
Practical Recommendations
For buyers and enthusiasts working with green coffee or purchasing through transparent importers, asking for the defect count per classification sample (350g) is a legitimate and revealing question. Specialty grade requires fewer than 5 Category 1 equivalents per 350g; premium grade allows up to 8; exchange grade allows significantly more. Beyond the numbers, the type of defect matters: a lot with a few Category 2 broken beans is much less alarming than one with even a single full black, because the former represents physical handling problems while the latter represents biological and fermentation failures that affect cup chemistry throughout the lot.