Faults present in the unroasted (green) coffee bean that no roast can rescue. Specialty grading systems exist precisely to count these — Q-grade and SCA both score a coffee partly by how few defects it contains per kilo.
The Specialty Coffee Association classifies them in two tiers:
Primary defects
The really damaging ones. Even a small number per kilo disqualify a coffee from specialty grade.
- Full sour beans: over-fermented in processing, taste sour, vinegary, sometimes rotten.
- Black beans: over-ripe and dried in cherry, taste fermented and harsh.
- Insect-damaged: bored by coffee borer beetle, taste musty.
- Foreign matter: stones, sticks, anything not coffee.
Secondary defects
Less severe but still flavor-impacting.
- Quakers: under-ripe beans that don't roast properly. Stay pale yellow when surrounding beans are brown. Taste papery, peanutty, hollow. The most common defect you'll see in light specialty roasts — visible quakers in the bag are normal up to a point.
- Floaters: beans that float in water during sorting; usually low-density, immature, or damaged. Taste flat.
- Withered: shrunken, ridged beans from drought-stressed cherries. Taste thin.
How they show up in your cup
A single sour bean in a brew can taste like rotten fruit hours after you've finished the cup — the off-notes linger. A few quakers just dull the average. The fix isn't on your end: it's the roaster's job to hand-pick visible defects after roasting (most specialty roasters do this). If your bag tastes consistently weird and you can spot pale, peanut-coloured beans, sort them out manually before grinding.