A sterilizing apparatus includes an enclosure defining an interior chamber and a door for accessing the interior chamber. A fluid source communicates with the chamber to supply a working fluid thereto. A heater heats the fluid in the chamber and a pump moves the fluid in the chamber by the heater. A valve communicates with the chamber and with the exterior of the chamber and is configured to vent the fluid in the chamber to the exterior at a pressure of approximately one atmosphere. Such provides superheating and concentrating of the working fluid in the chamber. A method of sterilization includes introducing a working fluid into an interior chamber and circulating the fluid through at least one recirculation loop having a heater for heating the fluid to an operational temperature suitable for killing microorganisms. The method further provides for killing of very high temperature resistant microorganisms.