In this work, several solid bed properties of compressible materials are examined with respect to their impact on batch and continuous processes, implying using dense gases. Important properties in this context are, amongst others, compressibility and permeability. Moisture and temperature are shown to strongly increase the compressibility of natural materials such as hops and caraway. Compressibility, on its turn is decisive for solid bed permeability at a given mechanical pressure. The combination of uniaxial compressibility experiments with permeability tests is introduced as a useful tool to evaluate the feasibility of various processes, especially oil/juice expression in a screw press, supercritical batch extraction, and continuous extrusion-extraction, where fluid flow through a solid bed is determinative for the process. In the case investigated, gas pressure differences over a solid bed can provoke a post-compression of the solid bed, which then leads to a decrease in permeability which strongly affects the whole process.