  Because of the presence of a liquid-gas phase transition in nuclear matter,
compact-star matter can present a region of instability against the formation
of clusters. We investigate this phase separation in a matter composed of
neutrons, protons and electrons, within a Skyrme-Lyon mean-field approach.
Matter instability and phase properties are characterized through the study of
the free-energy curvature. The effect of beta-equilibrium is also analyzed in
detail, and we show that the opacity to neutrinos has an influence on the
presence of clusterized matter in finite-temperature proto-neutron stars.
