TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Components: The rotatable filter further comprises a removable filtration basket including a drum frame and a mesh screen. The mesh screen is annealed. It is adapted to be removable. The drum frame is recyclable. The mesh screen is disposable. At least one inlet is adapted for continuous flow of the media from the bioreactor. At least one pump is adapted for providing continuous flow throughout the apparatus. The first outlet is adapted for continuous flow of media to the bioreactor. The second outlet is adapted for continuous flow to the harvest reservoir. A media-containing reservoir is adapted to be in fluid connection with the bioreactor. The separation apparatus is adapted to be sterilized by a steam supply source (341). It is adapted to be cleaned. The interior of the apparatus is capable of remaining isolated from the outside environment. At least one valve (210, 345, 360) for discontinuing fluid flow through the inlet into the filtration reservoir is in fluid connection with the inlet and the filtration reservoir. At least one valve (110) for discontinuing fluid flow through the first outlet to the bioreactor is in fluid connection with the first outlet and adapted to be in fluid communication with the bioreactor. At least one valve for discontinuing fluid flow through the second outlet to the harvest reservoir is in fluid connection with the second outlet and the harvest reservoir. An indication system in electrical communication with a personal computer (PC) controller comprises flowmeter for measuring flow of the separated media from the second outlet, a flowmeter for measuring flow of the liquid cell culture media containing the expressed protein fluid to the filtration reservoir or load cell(s) for measuring the weight of the cell culture. A pressure gauge is in connection with the filtration reservoir and adapted to measure the internal pressure of the filtration reservoir. At least one valve for releasing fresh media (10) from the media-containing reservoir to the bioreactor is in fluid connection with the media-containing reservoir and the bioreactor and adapted to release the fresh media in an amount equivalent to the fluid flow from the second outlet into the harvest reservoir. The flow from the bioreactor to the filtration reservoir to the bioreactor comprises a retentate circuit.    TECHNOLOGY FOCUS - METALLURGY - Preferred Materials: The drum frame and mesh screen are stainless steel.