What is chlorogenic acid in coffee?

Chlorogenic acids are a family of phenolic compounds found in high concentrations in green coffee - typically making up 6-10% of the dry weight of Arabica beans. They are one of the most significant chemical components in coffee, affecting both flavour and the body's physiological response to drinking it.

During roasting, chlorogenic acids break down progressively. At lighter roasts, some remain intact and contribute to the perceived brightness and complexity of the cup. As roasting progresses, they degrade into quinic acid and caffeic acid - compounds associated with the bitter, astringent character of darker roasts. This degradation is one reason why light roasts tend to taste brighter and darker roasts more bitter.

Robusta contains roughly double the chlorogenic acid content of Arabica, which is one factor contributing to the more bitter, harsher character of lower-grade Robusta in the cup. Chlorogenic acids have also attracted health research interest for their antioxidant properties, though the relevant compounds are largely destroyed in darker roasting.