The invention relates to a method of operating a pasteurization plant whereby containers filled with food products and closed are treated with a tempered aqueous process liquid in one or more treatment zone(s). At least a part of the process liquid is circulated around the treatment zone(s) for reuse in at least one recirculation loop. A partial quantity of the process liquid circulated in the at least one recirculation loop is removed and fed to a cleaning device comprising a membrane filtration device. A flow rate through the membrane filtration device is continuously monitored by means of a sensor device. A volumetric flow through the membrane filtration device is influenced by adjusting a flow regulating position of at least one adjustable flow regulating means. The at least one partial flow is then returned to a recirculation loop or a treatment zone again.