Discovered in 1932, chlorogenic acids (CGA) represent a large family of esterified compounds present in green and roasted coffee. During roasting, CGA's slowly decompose to form caffeic and quinic acid with about 50% of the original CGA being destroyed in a medium roast.
Quinic acid along with citric and malic represent a significant portion of coffee's total acid content. During roasting quinic acid progressively increases as the levels of chlorogenic acid decrease, suggesting that its formation results from the cleavage of the chlorogenic acid moiety.
In its pure state - caffeine, or 1,3,7-trimethylxanthine, exists as a white powdered alkaloid with an intensely bitter taste. Although coffee is most associated with caffeine, there are over 1,000 compounds in coffee making caffeine just a tiny fraction (~0.01%) of coffee's total composition.