The invented method adopts the semiproduct as raw material and accomplishes once through the saccharifying separating and boiling process. Said multifunction saccharifying tank possesses of a red copper seal, and a red copper tank body in which a stainless steel internal tank is installed, on the bottom of the tank body there is an outlet, from which the product in the tank is pumped out by the delivery pump and pumped in through the inlet, thus it onducts the continuous circulation and accomplishes the saccharifying, separating and boiling in the course of continuous circulation. Compared with the existing technologies, said method greatly simpifies the productive process, shortens the productive period and decreases the mumber of equipment and the occupied floor area.