Discovered in 1932, chlorogenic acids (CGA) represent a family of esterified quinic acid compounds  present in green and roasted coffee. During roasting, sixty percent of CGA is decomposed in medium roasts with the majority of the byproducts forming quinic and caffeic acid. Both quinic and caffeic acid have been associated with the increased levels of astringency, bitterness and body commonly seen as roasting progresses.

Coffee has by far the largest concentration of chlorogenic acid of any species in the plant kingdom, accounting for 6-7% d.b. in Arabica and up to 10% d.b. in Robusta⁵. CGA production in the plant is initiated by several factors including changes in environmental conditions, plant stress, and pest infestation. Its no surprise then, that robusta, while grown in harsher conditions have almost twice the concentration of CGA. CGA production also closely parallels with that of caffeine, such that, as CGA  concentrations increase so will caffeine. Interestingly in coffee, CGA concentrations far exceed caffeine levels by 5-7 times, yet up until the past decade much of the research on coffee research focused on solely on caffeine. Table 1 below summarizes caffeine, chlorogenic acid and protein concentrations in both arabica and robusta coffee.

It must be noted that although the term ‘chlorogenic acid’ typically refers to the 3-CGA mono-ester, it is sometimes used to refer to a larger family of compounds¹. Of these, three main categories of chlorogenic acids exist:  mono-caffeoylquinic, di-caffeoylquinic and feruloylquinic acids.

Interestingly, each isomers impart a distinct flavor characteristic. For example the "di-CGA" acids have been characterized many researchers as a metallic/bitter taste². Its no suprise then that Robusta coffees contain almost twice the concentration of di-CGA acids and may help explain why these coffee tend to be harsher in taste. Although a few savvy chemist have been able to slightly alter the CGA profile by steam treatment and thereby improving quality.

Research on coffee has confirmed that it contains a high concentration of antioxidants in the range of  200 to 550mg per cup (6oz) - a level far exceeding that of green tea. Although both coffee and tea contain high levels of antioxidants, coffee tends to contain higher levels of the simple phenolic compounds, whereas tea larger levels of catechins⁴.