Q: Is it true that roasting coffee can release dangerous airborne chemicals? Is this a risk for people working in coffee shops or even for those spending lots of time in them?
A: Yes, to the first question, but so far the health risk appears to be limited to certain workers in coffee-roasting facilities.
For decades there have been reports of respiratory problems among workers in coffee-roasting plants, which were often attributed to occupational asthma or emphysema. It was also thought that such problems may have been caused by two flavoring ingredients sometimes used for coffee—diacetyl (linked to bronchiolitis obliterans, a lung disease sometimes dubbed “popcorn lung” since it occurs in workers in factories producing popcorn or their flavorings) and the related compound 2,3-pentanedione.
But it turned out the processing of unflavored coffee can also cause bronchiolitis obliterans in workers exposed to the fumes, since both diacetyl and 2,3-pentanedione naturally form and are released when coffee beans are roasted, as well as when they are ground, when the coffee is packaged, and when containers of roasted coffee are opened.
In 2013 the CDC reported in Morbidity and Mortality Weekly about cases of bronchiolitis obliterans in former workers in a facility in Texas where coffee was roasted, ground, and flavored. In 2015 an investigation by the Milwaukee Journal Sentinel found levels of diacetyl and 2,3-pentanedione greater than government safety limits at two coffee-roasting facilities in Wisconsin.
In 2016 the CDC issued a warning to workers in coffee-processing facilities about the exposure to potentially dangerous levels of these chemicals and advised companies to test air levels and take steps to reduce exposures, if necessary.
What about workers in coffee shops? In two studies in Toxicology Reports in 2015, researchers tested the air in simulated coffee shops where a barista ground coffee beans. They found low levels of these two chemicals in the air—levels they considered unlikely to pose any danger.
Much remains unknown about the risk of inhaling coffee fumes, including what levels of the airborne chemicals are dangerous and how long the exposure needs to be to cause harm. People who work in coffee shops, especially those who grind lots of beans, should make sure there is good ventilation, which is important for dissipating the fumes. Some employers may require such workers to wear a respirator.
There’s no evidence, however, that consumers who visit coffee shops or prepare coffee at home need to worry about their health.