Key Aroma-Active Compounds (Volatiles)
These are primarily generated during roasting (Maillard reaction and Strecker degradation) and define the smell and, by extension, much of the perceived flavor. 
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- Furfural: Caramel-like, sweet, woody aroma.
- 2-Acetylfuran: Nutty, roasted aroma.
- Furfural acetate: Sweet, balsamic aroma.
- 5-Methylfurfural: Caramel-like, sweet aroma.
- -Butyrolactone: Nutty, caramel aroma.
- 2-Ethyl-5-methylpyrazine: Earthy, nutty, roasted aroma.
- Guaiacol: Smoky, phenolic, spicy aroma.
- 4-Ethyl-2-methoxyphenol: Smoky, medicinal, spicy aroma.
- 4-Vinyl-2-methoxyphenol: Smoky, phenolic, sweet aroma.
- 1-(2-Furanomethyl)-1H-pyrrole: Nutty, roasted aroma.
- Isovaleric acid: Cheesy, acidic, fruity note.
- 2-Methylbutanal: Fruity, malty note.
- 2-Methyl-2-butenal: Fruity note.
- 2-Furancarboxaldehyde: Woody, roasted note.
- Methyl phenylacetate: Honey-like, sweet, floral note.
- Dimethyl sulfide: Sulfur-like, savoury, or cabbage notes.
- Furanone: Sweet, caramel-like note.
- Thiols: Often associated with meaty or roasted aroma notes. National Institutes of Health (.gov) +4
Flavor Precursors and Non-Volatiles (Taste and Body)
These compounds exist in the green bean and directly affect the taste (bitterness, acidity, sweetness) or break down during roasting to create aroma.
19. Sucrose: A major sugar that caramelizes during roasting to produce sweetness and aroma compounds.
20. Caffeine: Responsible for up to 10-30% of the bitterness in coffee.
21. Trigonelline: Contributes to bitterness and forms niacin (nicotinic acid) and aroma-active pyridines during roasting.
22. Chlorogenic Acids (CGAs): Primary phenolic compounds responsible for astringency and bitterness; they break down into caffeic and quinic acid.
23. 3-Caffeoylquinic acid (3-CQA): A specific isomer of chlorogenic acid.
24. 4-Caffeoylquinic acid (4-CQA): A specific isomer of chlorogenic acid.
25. 5-Caffeoylquinic acid (5-CQA): A specific isomer of chlorogenic acid.
26. Quinic acid: A degradation product of chlorogenic acid; contributes to acidity.
27. Citric acid: Contributes to the pleasant acidity, particularly in high-altitude Arabica.
28. Malic acid: Contributes to a bright, fruity/sour acidity.
29. Acetic acid: Responsible for acidity and a sharp, vinegary sensation if in excess.
30. Lipids (fixed oils): Contribute to brew viscosity, body, and hold hydrophobic aroma compounds.
31. Polysaccharides (Cellulose/Galactomannans): Insoluble carbohydrates that contribute to the viscosity and body of the brew.
32. Melanoidins: Brown-coloured substances formed at the end of the Maillard reaction that contribute to body and colour.
33. Free Amino Acids (e.g., Glutamic acid): React with sugars in the Maillard reaction to create key volatile aromas.