Influences of Coffee Processing Stages and Variables on the Formation of Diacetyl and 2,3-pentanedione: A Field Assessment in a Café Setting

This study examined airborne α-diketones (diacetyl and 2,3-pentanedione), known respiratory irritants, across different coffee processing variables. A factorial design assessed the roast degree and processing stage, supported by separate tests on other factors. All experiments were performed in triplicate at a single site to reduce variability. Real-time measurements of total volatile organic compounds (TVOCs) and PM2.5 aerosols were also conducted when possible. Significant differences (p < 0.05) in α-diketone concentrations were found among processing stages (grinding > roasting > packaging), but not by roast degree. Grinding emitted much higher TVOC levels than roasting (1131.7 vs 88.3 ppb), while roasting produced higher PM2.5 (1079.6 vs 90.1 μg/m3). TVOC levels strongly correlated with diacetyl (r = 0.827) and 2,3-pentanedione (r = 0.848). Beans from Brazil (sun-dried) released more α-diketones than Ethiopian (washed) beans. Grinding zone levels of diacetyl and 2,3-pentanedione were 8.4 and 4.9 times higher, respectively, than in the nearby bar area (∼7 m away). Bean aging affected 2,3-pentanedione levels, peaking on the first day after roasting. Grind size and quantity showed no significant effects. These findings highlight key factors influencing α-diketone emissions, and reflect realistic exposures in café environment. Routine monitoring and source control are essential to protect worker and consumer health. Elevated PM2.5 levels during roasting also merit further study on their chemical characteristics and toxicity.