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The Hughes press and the 'X' press enable frozen cell pastes to be forced under high pressure (150 - 230 MPa, 10 - 15 tons per square inch) through narrow orifices, the disruption being produced by phase and volume changes and by solid shear due to the ice crystals. The Hughes press can only be used discontinuously on a small scale. The 'X' press may be used semi-continuously and is amenable to scale-up but, although the method allows the breakage of even the most robust organisms and the efficient recovery of heat-sensitive enzymes, freeze-pressing is not used on a large scale for releasing enzymes from cells.