Measurement of Diacetyl and Related Compounds in Coffee Roasteries and Breweries
Authors: Davey Nicholas G , Richards Larissa C , Davidson Jonathan , Michalchuk Trevor , Gill Christopher G , Krogh Erik T , Simpson Christopher D 
Published: October 2021

α-Diketones such as diacetyl (2,3-butanedione) and 2,3-pentanedione are generated during the roasting and fermentation of foods and are also used as flavoring compounds. Exposure to these compounds has been associated with obliterative bronchiolitis in workers. We report indoor air concentrations of diacetyl and 2,3-pentanedione, as well as acetoin (3-hydroxy-2-butanone), in several small coffee roasteries and breweries using standard integrated air sampling sorbent tubes followed by gas chromatography tandem mass spectrometry as well as the first use of on-site continuous real-time proton-transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS). Diacetyl and 2,3-pentanedione were detected in most of the sorbent samples at concentrations between 0.02 and 8 ppbv, and in general were higher in coffee roasteries compared with breweries. Three integrated air samples, all from the barista area at one facility, exceeded the NIOSH recommended exposure limit (REL) of 5 ppbv for diacetyl. 2,3-Pentanedione concentrations in these three samples were greater than 50% of its REL, but did not exceed it. Acetoin, a precursor to diacetyl, was also detected at concentrations between 0.03 and 5 ppbv in most sorbent tube samples, with concentrations generally higher in breweries. PTR-ToF-MS measurements exhibited similar trends and provided continuous real-time volatile organic compound data that showed episodic excursions with peak concentrations of diacetyl and 2,3-pentanedione between 15 and 20 ppbv. Examination of the time series data identified specific activities associated with peak diketone emissions, including transfer of freshly roasted coffee beans to the cooling tray, or the opening of a brew kettle. Additional indoor air quality parameters including CO2, NO2, and PM2.5 were also assessed on-site. Airway inflammation was assessed in 19 workers before and after each work shift using online measurements of fractional exhaled nitric oxide (FENO). The pre-shift mean FENO was 3.7 (95% confidence interval: −3.6, 11.0) ppbv higher and the post-shift FENO was 7.1 (−1.9, 16.1) ppbv higher for workers at coffee roasteries compared with breweries. The cross-shift change in FENO was 3.4 (−2.8, 9.6) ppbv higher for workers at coffee roasteries compared with breweries. However, none of these differences were statistically significant, and the cross-shift change in FENO was not statistically different from zero for either group of workers. The findings from this pilot study demonstrate that α-diketones and related compounds are present in the indoor air of both breweries and coffee roasteries and may exceed health protective guidelines in coffee roasteries. Additional studies are required to fully characterize worker exposures in these settings and to identify specific work activities and processes associated with high exposures. Engineering controls, including targeted exhaust ventilation and the use of low-cost sensors, are recommended as an approach to protect workers from exposure to hazardous levels of α-diketones.