The reason is that when coffee beans are roasted, harmful substances like benzo[a]pyrene (BaP) and acrylamide (ACR) can be produced due to the high temperatures involved. These substances are especially prevalent in dark roasting, where chemical reactions occur, creating compounds considered potential carcinogens. Benzo[a]pyrene is a type of polycyclic aromatic hydrocarbon (PAH) formed through incomplete combustion, while acrylamide results from a reaction between sugars and amino acids during the roasting process.
Dark roasting produces beans that are almost too black in color, often with an oily
surface and reduced acidity.
These beans are roasted the longest, which enhances caramelization and gives them a distinct dark chocolate flavor. However, the uniqueness of the coffee's flavor can be masked by roasted notes, bitterness, and sometimes a smoky flavor. This style of roasting is commonly
used for traditional Italian espresso.
Due to the bitterness and strong body of dark-roasted coffee, it often requires
more milk, cream, or sugar.