A device for separating components of a composition according to density. The device includes a rotatable chamber and a plurality of buoys. The rotatable chamber has an axis of rotation. The plurality of buoys are positioned within the rotatable chamber and about the axis of rotation. The buoys are radially movable between an expanded position in which the buoys are at a first location relative to the axis of rotation and a contracted position in which the buoys are at a second location relative to the axis of rotation. The first location is further from the axis of rotation than the second location is. The buoys are movable in response to force generated during rotation of the rotatable chamber.