The invention relates to a method for separating blood to a separation container and to a system wherein different blood fractions erythrocytes (64) buffy coat (65) and blood plasma (66) are obtained wherein blood is introduced into a separation container (1) and is then centrifuged into different superimposed fluidically connected sections of the separation container specifically a top section (4) for receiving the blood plasma (66) a middle section (3) for receiving the buffy coat and a bottom section (2) for receiving the erythrocytes (64). The aim of the invention is to optimize the extraction of buffy coat. Said aim is achieved by means of the method and the separation container wherein the optimization is geared to obtaining a defined phase boundary and by means of the system wherein the optimization is geared to achieving freedom from contamination from the time the blood enters the separation container and obtaining an easy to handle freezer container for cryopreservation. By means of the haematocrit of the blood supplied the future packing volume of the erythrocytes (64) to be centrifuged is determined. Furthermore the capacity of the bottom section (2) is adjusted to the expected packing volume of the erythrocytes after the centrifuging in such a manner that the phase boundary (5) forming during centrifuging between buffy coat (65) and erythrocytes (64) is positioned in a region of the middle section (3) of the separating container (1) adjacent to the bottom section (2) and finally the amount of blood supplied is introduced in the exact volume into the separation container (1) taking into account the expected packing volume of the erythrocytes (64). The separation container (1) enables the method to be carried out. The system is kept closed and avoids interaction with the environment.
