A beverage brewing device includes a lower container for receiving and heating water, a connected upper container for receiving beverage, and a piston-cylinder assembly for receiving grounds, captured within the lower container. The piston-cylinder assembly includes a cylinder, a piston movable in the cylinder, a conical diffuser fixedly attached to the piston, and a freely movable mass disposed between the piston and the conical diffuser. The piston and the conical diffuser define an expansion chamber therebetween. The chamber is formed between a diffuser plate forming the top of the piston and an inner conical surface of the diffuser, which defines an orifice functioning as a nozzle. The diffuser plate has a plurality of holes, on which the grounds are placed. The mass is seated at a valve seat at the entrance of the expansion chamber to operatively block the flow of fluid through the nozzle when the pressure of the fluid is insufficient to displace the weight of the mass. When water is heated in the lower container becomes pressurized sufficiently to pass through the nozzle and displace the seated mass from the valve seat, the water passes through the nozzle at relatively high pressure and velocity, and enters the expansion chamber at lowered pressure. It then flows through the diffuser plate, through the grounds, and into the upper chamber.