A centrifugal separation apparatus comprises a rotatable cylindrical member (136) including a side perforated wall and an opened bottom and a bottom lid member (138) including a central raised portion and a side wall inclined downwardly and outwardly. The bottom lid member (138) is moveable between an upper position in which said bottom lid member is engaged by the lower end face of said cylindrical member (136) and a lower position in which said bottom lid member is spaced apart from the lower end of said cylindrical member (136) to form a gap therebetween.