Watchdog Piece Suggests Toxic Compound Diacetyl May Pose Risk to Roasters’ Health

Roasted coffee in a cooling tray. 2010 Creative Commons photo by Michael Allen Smith

A report from the Milwaukee Journal Sentinal suggests commercial coffee roasteries may be putting the lung health of their employees at risk through exposure to a toxic chemical compound known as diacetyl.

Diacetyl, known for a buttery flavor, is a chemical compound found in many foods and drinks, such as beer, wine and yogurt, and the United States Food and Drug Administration maintains that it is safe to ingest in small amounts. But when diacetyl is inhaled in unsafe amounts, it can cause a potential deadly or debilitating lung disease known as bronchiolitis obliterans, also known as constrictive bronchiolitis, which causes small airways to be constricted by fibrosis.

Unhealthy levels of diacetyl have most commonly been associated with the production of popcorn or other chemically flavored products. The chemical compound has been at the center of a much-publicized case involving the deaths of multiple people who worked at a facility in Tyler, Texas, where coffee was being roasted and flavored.

The Journal-Sentinel piece provides one of the only known studies of the compound in unflavored-coffee roasting environments. And although the sample size is undeniably small, and remarkably few known cases of bronchiolitis obliterans have been associated with commercial coffee roasting, the results may warrant further study.

Journal Sentinel reporter Raquel Rutledge contacted several Wisconsin roasteries for the story, asking if the organization could test for the air in production areas where coffee was being roasted and/or ground. While several prominent roasteries declined, Milwaukee’s Valentine Coffee Roasters and Madison’s Just Coffee Cooperative accepted the invitation.

Both roasteries are known to have modern airflow and ventilation systems designed to mitigate the potential for poor air quality, yet the tests showed that diacetyl levels exceeded what the National Institute of Occupational Health and Safety considers, in a current draft report, the target maximum levels for employee safety. That draft currently suggests 5 parts per billion as the exposure limit during the course of an eight-hour shift. At Just Coffee’s two roasters, the Journal Sentinel testing revealed levels of 6.9 and 8.1 ppb, while Valentine’s roasting area showed a level of 7.44 ppb. The tests showed exponentially higher diacetyl levels where coffee is ground — 19.3 and 19.6 ppb, respectively.

We followed up with Just Coffee Co-Founder Matt Earley, who says the presentation of the data related to grinding may not reflect actual exposure in JCC’s production facility.

“The MJS took the two hour tests and extrapolated them out over an eight hour day,” Earley tells Daily Coffee News. “The grinding numbers being four times higher than recommended exposure levels is a little confusing. They ran those numbers to reflect an eight-hour grinding shift. We generally do not do shifts over two hours, and over three is unheard of, so that number is a higher than any actual exposure here.”

Earley suggests diacetyl is largely unknown throughout the coffee roasting industry, and says JCC “jumped at the chance” to have the facility tested when approached by Rutledge.

“We always want to be on the leading edge of making sure that our business lives up to our principles and our ethics,” Earley says. “If there is even a chance that our people our being exposed to something potentially harmful, we want to get on top of it. I am frankly surprised so many roasters turned her down, but I feel like now that more information will be coming out on this that other roasters will take it seriously and do what they need to do to protect their workforce.”

Read the full Journal-Sentinel piece, which followed interviews with numerous people outside and inside the industry, including SCAA Executive Director Ric Rhinehart, who points out a lack of epidemiology related to bronchiolitis obliterans throughout coffee roasting’s history.

The National Coffee Association, for one, released an official position statement on diacetyl in May of this year, as the U.S. Centers for Disease Control and Prevention is currently in the draft stage of new safety standards related to the compound. The NCA statement reads, in part:

The National Coffee Association (NCA) is aware of isolated instances where environmental exposure to large quantities of synthetic diacetyl in flavorings has been cited as causing a very rare health condition called Bronchiolitis Obliterans (BO). These instances had the commonality of exceedingly high exposure to synthetic diacetyl in flavorings under poor plant hygiene conditions, which included improper ventilation and absence of personal protective equipment.

For naturally occurring diacetyl as a byproduct of roasting coffee, there are well-established safety protocols and procedures designed and deployed to eliminate worker exposure. Commercial coffee roasting ovens are generally “closed systems” that are built to channel smoke, chaff, volatiles like diacetyl, and other natural byproducts of roasting through closed pipes to exhaust stacks. After roasting, coffee is released onto “cooling carts” (basically large circular trays), since the beans must be immediately cooled to arrest further roasting that would impact flavor profiles. While some systems have closed cooling carts, standard practice for open cooling carts involves air and volatiles being sucked down through holes in the bottom of the cooling tray as ambient air necessary for cooling is drawn down by fans through the beans and out below through the holes. The air and volatiles drawn down in the cooling carts is then channeled by pipe into exhaust stacks that vent the air externally. Stemming from these protocols and procedures, there has been no proven connection between the natural roasting byproduct diacetyl and obstructive lung disease.

We’ll have more on this subject as it develops.