Green Coffee Defects and Their Aroma-Relevant Precursors: A Review of Classification Systems, Causal Pathways, and Sensory Chemistry

Green coffee defects are evaluated worldwide as visible abnormalities, physical damage, foreign matter, or off-odor, yet the relationship between grading label and cup quality is neither direct nor uniform. This review integrates international and national classification systems with evidence on defect formation, green bean composition, roasting chemistry, and sensory consequences. It shows that standards differ in sample mass, counting basis, legal status, and intended purpose, so their values cannot be converted into a common sensory scale. Defects are best understood as disturbances to precursor pools or as processing and safety risks; they are not fixed flavor entities. Compositional and volatile differences relative to sound coffee are documented for black, sour/brown, immature, insect-damaged, and aged beans; many other visible categories lack defect-specific odor-active or dose–response data. The term quaker illustrates the central nomenclature problem: standards commonly link it to immature beans, whereas a differentiated physiological position treats emaciated beans as a separate pathway. Rio flavor and potato taste defect provide more specific chemical signatures than most visual defects. A precursor-centered framework is proposed to connect grading with analytical and roasting practice while retaining uncertainty where the evidence chain is incomplete.