A sterilization apparatus for sterilization of objects. The apparatus includes a chamber for receiving the objects including a sterilization medium inlet and outlet； an inlet flow control device for controlling a supply of a sterilization medium to the chamber； a drain system for controllable discharge of fluid from the chamber； and a control unit configured to control the inlet flow control device and drain system. The drain system includes: a drain inlet connected to the sterilization medium outlet； a drain outlet connected to a vacuum system for evacuating the chamber； a first conduit connecting the drain inlet and outlet； and a proportional valve, arranged along the first conduit, controllable by the control unit to partly restrict fluid flow through the first conduit according. Drain valves may be controlled in response to the temperature of a flow of coolant, the coolant being used for cooling fluid via a heat exchanger.
