Taste perceived by the palate. It is a taste not generally appreciated by humans, particularly in high concentrations, as it is often found in poisons and toxic substances in nature.
It is usually always discernible in a cup of coffee, as it is generated by the chemical reactions that occur during
the roasting process, and is pleasant, and therefore appreciated, in low concentrations.

Extractions prepared using the Canephora species coffee (commonly known as Robusta) are usually more bitter than those prepared using the Arabica species.
This is in part because the concentration of caffeine (itself very bitter) in Robusta is almost double that found in Arabica (1.8- 3.5% compared to 0.7-1.5%). Robusta also has a higher concentration of chlorogenic acid (7-10%
compared to 5.5-8%) which – particularly in the case of dark roasts – breaks down into quinic acid and caffeic acid, both of which are very bitter.
In general terms, dark roasts are associated with much more bitter notes in the cup.