The invention relates to a method for extracting cells from blood or from blood products, said method comprising the following steps: (i) a blood bag (35) containing a blood product is placed in a blood bag region (5) of an insert (1)； (ii) a tube (36) connected to the blood bag (35) is inserted into a product transport path (36) connecting the blood bag (35) to a product bag (33), a first sensor (25) and a second sensor (85) being positioned along the product transport path (36)； (iii) the insert (1) is inserted into the rotor of a centrifuge； (iv) the centrifuge is rotated in order to separate the individual blood constituents； (v) a pre-determined quantity of a blood constituent is transported along the product transport path (36) at a first flow speed； and (vi) the composition of the transported blood constituent is detected by the first sensor (25). The second sensor (85) also detects the composition of the transported blood constituent, according to a signal corresponding to a pre-determined composition of the blood constituent and emitted by the first sensor (25). The transport and rotation are stopped when the second sensor (85) detects the pre-determined composition and emits a corresponding end signal, or when a pre-determined period of time has elapsed.
