How Roasting Coffee Affects Aromatic Compounds

Roasting coffee is a process that greatly increases the aroma, taste, flavor, usability and health giving antioxidant chemicals in coffee. However it is also known to have some negative impacts such as the creation of mutagenic and carcinogenic compounds such as acrylamides and polycyclic aromatic hydrocarbons.

To investigate the negative impacts of roasting on the quantity of polycyclic aromatic hydrocarbons Houessou and colleagues from France investigated filtered Arabica coffee and coffee brews for hydrocarbon levels.

Methodology of the Investigation into Hydrocarbons in Coffee

In general Houessou and colleagues were thorough carrying out coffee analysis in triplicate when possible. They tested green Arabica coffee beans sourced from Cuba and roasted the beans using a spouted bed roaster. After a roasting of either 5 or 20 minutes the coffee beans were ground and extracted by use of a pressurized liquid extraction system. For the coffee brew analysis, coffee was prepared by the filter method using 50g of ground coffee.

Findings of the Analysis of Polycyclic Aromatic Hydrocarbons in Coffee

It was found that un-roasted green coffee beans contained a similar amount of polycyclic aromatic hydrocarbons as coffee that had been roasted for 20 minutes. The largest components of the polycyclic aromatic hydrocarbons found in roasted coffee were phenanthrene, pyrene and fluoranthene. It was found that these three hydrocarbons increased in concentration when the temperature of the roasting conditions increased. In addition to this it was found that roasting at a temperature of 260 degrees Centigrade led to an increase in both benzo[a]anthracene and chrysene. The most toxic polycyclic aromatic hydrocarbons compounds are benzo[a]pyrene and dibenzo[a,h]anthracene; these were either not found or present at very low levels in coffee that had been subjected to a strong coffee roasting process.

In lightly roasted coffee (5 minutes of roasting) the phenanthrene, pyrene and fluoranthene hydrocarbons were still present, however neither benzo[a]anthracene nor chrysene was found, strongly suggesting that it was the longer roasting process that led to the formation of these two hydrocarbons in the coffee.

The investigation of the brewed coffee led to the discovery that the levels of aromatic hydrocarbons that passed from the ground roasted coffee to the brewed coffee was fairly significant at around 35%. It was noted by the authors that if a coffee was darkly roasted it would pass on less hydrocarbons into the coffee brew than a lightly roasted coffee would.

References
Houessou et al (2007). Effect of roasting conditions on the polycyclic aromatic hydrocarbon content in ground Arabica coffee and coffee brew. J.Agric. Food Chem.