Influences of coffee roasting stages and variables on the formation of diacetyl and 2,3-pentanedione: A field assessment in a café setting

This study examined airborne alpha-diketones (diacetyl and 2,3-pentanedione), known respiratory irritants, across different coffee processing variables. A factorial design assessed 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 (TVOC) and PM _2.5 aerosols were also conducted when possible. Significant differences (p < 0.05) in alpha-diketone concentrations were found among processing stages (grinding > roasting > packaging), but not by roast degree. Grinding emitted much higher TVOC than roasting (1131.7 vs. 88.3 ppb), while roasting produced higher PM _2.5 (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 alpha-diketones than Ethiopian (washed) beans. Grinding zone levels of diacetyl and 2,3-pentanedione were 8.4 and 4.9 times higher, respectively, than n 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 alpha-diketone emissions, and reflect realistic exposures in café environment. Routine monitoring and source control are essential to protect worker and consumer health. Elevated PM _2.5 levels during roasting also merit further study on their chemical characteristics and toxicity.