A method of washing blood mixed with undesirable elements not normally found in healthy whole blood to remove the undesirable elements, the method comprising: separating the blood into components according to relative densities of the components with a rotating centrifuge bowl providing a port through which fluid exits the bowl, the exiting fluid having a concentration of undesirable elements flowing washing solution into the centrifuge bowl at an initial flow rate monitoring the fluid exiting the bowl with an optical sensor having an output signal indicative of the composition of the exiting fluid and increasing and decreasing the flow rate of the wash solution as a function of the output signal.
