Abstract: The present invention relates to a process and apparatus for treating matter comprising a solid phase and a liquid phase, according to which said matter is crushed and the crushed matter is sifted under pressure, wherein the sifting under pressure and the crushing of the matter are effected simultaneously by disposing said matter in a closed so-called pressure chamber, causing at least one punch to advance in said chamber and expelling sifted matter through calibrated orifices in the pressure chamber. The invention is applied more particularly to the treatment of household garbage.