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.
Like many living organisms, citric acid plays an important role as a key intermediate compound in the plant's metabolic cycle. In green coffee citric acid makes up a significant portion of coffee's total acid content and ultimately in the development of perceived acidity.
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.
In coffee there are over two dozen different types of organic acids such as citric, malic, acetic, quinic, etc. But there is another branch of acids – inorganic acids – that are also believed to play an important role. One inorganic acid that has receive much attention is a phosphoric acid.
Acetic acid, or more commonly known as vinegar, is one of the many organic acids that play an important role in coffee quality. Although, there are varying levels found in both dry and wet processed coffees, its formation during post harvest processing comes primarily from fermentation.