A plunge-mixing bag arrangement includes a flexible mixing bag defining a mixing region, and a shaft extending from outside of the flexible mixing bag into the mixing region, the shaft comprising a sparger within the mixing region. The sparger comprises an interior channel and ports extending from the interior channel. The shaft is capable of axial movement within the bag to fracture gas bubbles being released from the interior channel through the ports. A plunge-mixing system includes a mechanism for raising and lowering the shaft.