NOVELTY - The method involves breaking down a cellular structure of the organic matter using thermal pressure hydrolysis in which pressure hydrolysis reactor (R) is pressurized by a piston of the pressure hydrolysis reactor in order to subject the organic matter to a hydrolysis pressure effect. The pressure hydrolysis reactor is heated in order to subject the organic matter to a hydrolysis heat effect.    USE - Method for preprocessing organic matter such as slurry and liquid manure used for generation of biogas.    ADVANTAGE - Efficient preprocessing of organic matter can be performed, so that the processed organic matter can be used for biogas production. Thus, the biogas production process can be performed efficiently, and the heat value of biogas can be increased. The organic matter such as slurry can be transferred easily, and the usage of several pumps can be reduced. Thus, the investment cost, service cost and malfunction of the equipment for preprocessing organic matter can be reduced.    DETAILED DESCRIPTION - The hydrolysis pressure of 20 bars is generated in the pressure hydrolysis reactor, during thermal pressure hydrolysis. The organic matter is divided into liquid and residual matter having a higher total solid content. The residual matter is preheated between the fractionation and thermal pressure hydrolysis. The residual matter is preheated in a heat exchanger (HEX). The organic matter is separated into liquid and residual matter having higher total solid content by pressurizing in the fractionation. The residual matter contained in the pressure hydrolysis reactor is heated. An INDEPENDENT CLAIM is included for equipment for preprocessing organic matter, which has a pressure hydrolysis reactor and heating unit. The pressure hydrolysis reactor has an inlet (IN) for the organic matter and an outlet (OUT) for processed organic matter. The pressure hydrolysis reactor is provided with movable piston. The heating unit for heating the pressure hydrolysis reactor, is provided with a heatable sheath of the pressure hydrolysis reactor. The fractionator (D) is configured to divide the organic matter into liquid and residual matter having higher total solid content. The fractionator is connected to the inlet of the pressure hydrolysis reactor in order to convey the residual matter from the fractionator to the pressure hydrolysis reactor. A heat exchanger is arranged between the fractionator and the pressure hydrolysis reactor. A mixing unit (MX) is provided for mixing the organic matter contained in the pressure hydrolysis reactor. A pressure disintegrator (PD) is connected to the pressure hydrolysis reactor.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the hydrolysis reactor and fractionator.    Fractionator (D)    Heat exchanger (HEX)    Inlet (IN)    Mixing unit (MX)    Outlet (OUT)    Pressure disintegrator (PD)    Pressure hydrolysis reactor (R)