A bean roasting system includes a roasting chamber, a blower, a variable diverter and a controller. The roasting chamber, the blower and the variable diverter each is disposed at least partially within a recirculating gas flow path. The blower is configured to provide a flow stream of gas through the recirculating gas flow path. The variable diverter is configured to split the gas flow path into at least two flow paths including a treated flow path and a bypass flow path. The treated flow path includes a series arrangement of a gas heater and a catalytic converter. The variable diverter is configured to control a percentage of a flow stream of gas that is diverted into the bypass flow path. The controller is configured to activate different predetermined operating modes for the bean roasting system by controlling a state of the variable diverter and a state of the heater.