Various compounds, including caffeine, that are present in coffee beans have antimicrobial properties. Additional Maillard reaction products that have antimicro

Various compounds, including caffeine, that are present in coffee beans have antimicrobial properties. Additional Maillard reaction products that have antimicrobial properties are created by roasting. Coffee is also pretty acidic - IIRC, dorm cafeteria coffee turned chem lab blue litmus paper a pretty red.