tags: [] - coffee/green-beans - coffee/processing - coffee/tasting aliases: - Coffee defects - Green coffee defects - Coffee grading defects

Common Defects¶

Tags: #coffee/green-beans #coffee/processing #coffee/tasting Aliases: Coffee defects, Green coffee defects, Coffee grading defects Related: Coffee Tasting MOC | Green Coffee Grading | SCA Cupping Protocol | Coffee Quality and Grading | Processing Methods MOC Status: ✅ Complete

Overview¶

Coffee defects are physical or sensory characteristics that negatively affect quality, arising at any stage from growing through processing, storage, and roasting. The Specialty Coffee Association (SCA) classifies green coffee defects as Category 1 (primary, severe) or Category 2 (secondary, moderate), with maximum tolerances used to determine whether a lot qualifies as specialty grade. A single primary defect can disqualify a sample; specialty grade requires zero primary defects and no more than five secondary defects in a 350 g sample.

SCA Defect Classification¶

Category 1 (Primary) Defects¶

Primary defects impose severe cup impacts; each defect instance counts as one full defect in the grading sample.

Defect	Description	Cup impact
Full black bean	Bean entirely blackened — over-fermentation, pod-borer damage, or fungal infection	Dirty, fermented, phenolic; ruins cup
Full sour bean	Entire bean excessively acidified from fermentation defect	Vinegary, rotten flavour
Dried cherry (pod)	Whole or partial dried cherry not removed during processing	Earthy, phenolic, composty
Fungus damaged	Mould or fungal growth visible; discolouration (yellow/brown patches)	Musty, mouldy; potential mycotoxin risk
Severe insect damage	More than three holes from coffee berry borer or other insects	Harsh, unpleasant; flavour contamination
Foreign matter	Sticks, stones, or non-coffee material	Safety and equipment risk

Category 2 (Secondary) Defects¶

Secondary defects are less severe; five defective beans equal one full defect in the count.

Defect	Description	Cup impact
Partial black bean	Portion blackened but not entirely	Moderate taint
Partial sour bean	Partial fermentation defect	Mild sourness
Parchment	Dried parchment (endocarp) remaining on bean after hulling	Papery, woody, astringent
Floater	Low-density bean that floats in water sorting	Poor development; baked or flat in cup
Immature / quaker	Under-ripe bean; fails to roast properly	Peanutty, papery, astringent
Broken / chipped bean	Mechanical damage during processing or milling	Uneven extraction; minor taint
Hull / husk	Dried cherry skin or pulp fragment	Earthy, grassy
Shell	Cup-shaped malformed bean from developmental defect	Uneven roasting
Withered	Shrivelled bean from drought or poor development	Under-roasts like quaker

Key Defect Types in Detail¶

Quaker¶

A quaker is an unripe bean that fails to roast at the same rate as mature beans, remaining pale tan or blonde after roasting while surrounding beans darken. Quakers are visually identifiable in the roasted lot and must be hand-sorted before packaging. Cup contribution: peanutty, papery, astringent. A single quaker in a cup is detectable and reduces score significantly.

Black Beans¶

Full black beans result from over-fermentation, pod-borer (Hypothenemus hampei) damage, or fungal infection during drying. They are a Category 1 defect because even one or two beans in a brew can produce phenolic, medicinal, or putrid notes that contaminate the entire cup.

Sour and Stinker Beans¶

Sour beans contain excessive acetic or butyric acid from fermentation defects — over-fermentation (too long in tanks or wet cherry pile) or microbial contamination. A stinker is the extreme form: a single stinker bean produces putrid, rotting odour detectable when crushed, and its cup impact extends well beyond the individual bean's volume.

Phenolic and Rio Defects¶

Phenolic flavours (medicinal, iodine-like, chemical) can arise from multiple defect sources: stinkers, over-fermentation, or specific microbial activity. The Rio or Rioy defect is a specific phenolic/iodine character associated primarily with certain Brazilian coffees, historically linked to bacterial contamination during sun-drying. Rio is commercially acceptable in some commodity markets but incompatible with specialty grade.

Fungus-Damaged and Earthy Defects¶

Fungal contamination during drying or storage produces musty, mouldy, or cardboard-like notes. Beyond quality impact, mycotoxin-producing moulds (particularly Ochratoxin A from Aspergillus and Penicillium species) are a food safety concern. Earthy notes (muddy, soil-like) can result from soil contact during drying, improper storage, or mould contamination — common in lower-quality Indonesian natural-process coffees.

Defect Detection Methods¶

Visual Sorting¶

Hand or electronic inspection of green or roasted beans to identify and remove defective specimens. Multiple passes reduce defect counts progressively. Skilled sorters achieve high accuracy; electronic colour-sorters are common in high-volume processing.

Density Sorting¶

Water-based flotation or air classification separates beans by density: low-density beans (floaters, immature, damaged) are removed first. Widely used as a pre-processing quality gate at wet mills.

Optical/Electronic Sorting¶

Camera-equipped sorting machines using colour, size, and shape data to detect and eject defective beans with air jets. High throughput and accuracy; widely used by exporters and dry mills.

Key Facts¶

SCA specialty grade: zero Category 1 defects and maximum five Category 2 defects in a 350 g sample
Category 1 defects (full black, full sour, dried cherry, fungus damaged, severe insect damage, foreign matter) each count as one full defect
Category 2 defects require five instances to equal one full defect in the grading count
A single stinker bean can contaminate an entire brew — extreme fermentation defect producing putrid odour detectable at the cup
Quakers are identified and removed from roasted lots — they remain pale after roasting and contribute peanutty, papery notes

References¶

Changelog¶

Date	Change
2026-05-02	Compliance review: full rewrite — replaced bold pseudo-header glossary format; added frontmatter, metadata block, Overview, defect tables, Key Facts, References, Changelog, copyright

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