The problem of mass transfer during the removal of the liquid from expressed biological particles is presented in one-dimensional formulation. The biological material is conceptualized as a double-porosity. When this material undergoes a pressing, the liquid flows in two volumes: (1) in a porous medium of sliced particles and (2) in the extraparticles network. An interporosity flowing occurs between these two porous volumes. The mathematical model relies on two differential equations of consolidation with initial and boundary conditions. The exact analytical solution of the problem is found through the application of the Laplace integral and Fourier transformations. The relevance of the numerical analysis is evaluated from some values of the process parameters. (c) 2006 Elsevier Ltd. All rights reserved.