7 Most Common Types of Defects
Table of Contents
Green coffee beans can have many types of defects — some are easy to spot, such as stones or sticks, while others require more observation, like full black beans or full sour beans.
Understanding these defects helps you classify and assess coffee quality following the SCA Arabica Green Coffee Classification Form.
1. Black Beans (Full Black)
Cause:
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Overripe cherries during harvest.
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Over-fermentation during processing.
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Poor storage conditions (high humidity).
Classification:
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Primary defect: 1 fully black bean = 1 full defect.
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Secondary defect: 3 partially black beans (half or less) = 1 full defect.
Impact:
Black beans produce unpleasant flavors — fermented, moldy, dirty, or phenolic tastes.
Prevention: Harvest ripe cherries, avoid over-fermentation, and dry coffee promptly.
2. Sour Beans (Full Sour / Brown Beans)
Cause:
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Overripe or fallen cherries.
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Excess fermentation or contact with polluted water.
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Prolonged storage before processing.
Classification:
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Primary defect: 1 fully sour bean = 1 full defect.
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Secondary defect: 3 partially sour beans = 1 full defect.
Impact:
Sour beans cause rotten, vinegary, or foul odors and unpleasant sourness in cup flavor.
Prevention: Pick only ripe cherries, process quickly after harvest, use clean water, and dry efficiently.
3. Dried Pod / Cherry
Cause:
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Poor separation during wet processing (light beans not removed).
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Improper hulling or sorting during dry/natural processing.
Classification:
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Primary defect: 1 dry cherry = 1 full defect.
Impact:
Can produce bitter, harsh tastes and promote mold growth.
Prevention: Ensure proper pulping, sorting, and machine maintenance.
4. Insect Damage
Cause:
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Infestation by Coffee Berry Borer (Hypothenemus hampei) or similar pests.
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Eggs laid in unripe fruits; larvae bore holes through beans.
Classification:
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Primary defect: 5 beans with severe insect damage (≥3 holes) = 1 full defect.
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Secondary defect: 10 beans with 1–2 holes = 1 full defect.
Impact:
Causes musty, sour, or burnt flavors.
Prevention: Use pest control measures, maintain hygiene, and harvest timely.
5. Floaters / Bleached Beans
Cause:
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Poor drying or uneven moisture loss.
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Beans stuck in corners of dryers or left too long on drying patios.
Classification:
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Secondary defect: 5 floaters = 1 full defect.
Impact:
These low-density beans cause grassy, earthy, or moldy notes.
Prevention: Ensure even drying and proper moisture control.
6. Broken / Chipped Beans
Cause:
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Excessive friction or pressure in pulpers, hullers, or mills.
Classification:
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Secondary defect: 5 broken beans = 1 full defect.
Impact:
Usually mild but can lead to oxidized or fermented flavors if excessive.
Prevention: Adjust pulper pressure and screen by density before storage.
7. Shell Beans (Elephant Ears)
Cause:
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Malformation of the cherry during development.
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Bean splits into two thin, separate parts.
Classification:
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Secondary defect: 5 shell beans = 1 full defect.
Impact:
Shell beans are thin, light, and tend to burn easily during roasting, causing smoky or bitter tastes.
Other Common Defects
Quaker (Unripe Beans)
Immature beans with low sugar and amino acid content that don’t caramelize properly when roasted.
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Impact: Burnt popcorn or paper-like taste.
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Note: Specialty coffee must have zero quakers.
Prevention:
Harvest only ripe cherries and use flotation to remove underdeveloped beans during wet processing.
Fungus Damage (Moldy Beans)
Caused by Aspergillus, Penicillium, Fusarium, etc. Spores can infect beans at any stage of processing if humidity is high.
Impact: Musty, earthy, fermented, or phenolic off-flavors.
Prevention:
Avoid collecting fallen cherries, ensure quick drying, and store in dry, ventilated conditions.
Withered Beans
Caused by drought during fruit development — beans become shriveled, light, and uneven.
Impact: Produce grassy or straw-like flavors.
Prevention: Remove by flotation or density sorting.
Visible Impurities
Pieces of husk, twigs, stones, or nails can be found in poorly processed lots.
These not only degrade appearance but can damage roasters or grinders.
Final Note
Even when green coffee appears physically clean, it may still produce poor flavor.
That’s why defect analysis is only one step in the broader quality control process for specialty coffee.