A method for inactivating a fluid culture includes inserting a collapsible bag within a chamber of a tank assembly. A fluid is dispensed into a compartment of the collapsible bag, the fluid including a culture containing live cells or microorganisms. A lid is positioned over an opening of the tank assembly so that the collapsible bag is substantially enclosed within the tank assembly. The fluid within the collapsible bag is heated to an inactivation temperature that is sufficiently high to kill all of the live cells or microorganisms within the fluid. In one embodiment, the fluid within the flexible bag is mixed while the fluid is being heated to the inactivation temperature.
