Method and apparatus for separating a volume of composite liquid into at least a first component and a second component including centrifuging a separation bag (1) containing a volume of composite liquid and a volume of gas so as to sediment at least a first component and a second component separation bag (1)； displacing a volume of hydraulic fluid against the separation bag to cause a transfer of at least one fraction of the content of the separation bag (1) into at least one component bag (2, 3, 4, 5) connected to the separation bag (1)； determining the volume of hydraulic fluid displaced and determining the volume of the composite liquid or the transferred components from the determined volume of displaced hydraulic fluid.
