Abstract: Plant for briefly heating a free-falling liquid in a pressure chamber (9) by stream which is also supplied to the pressure chamber. The liquid is supplied to the pressure chamber through a supply plate (42) provided with channels (44) and the resulting liquid jets are brought into contact with the steam. Over the thickness of the plate a temperature gradient is maintained at the level of the difference between the steam temperature and the supply temperature of the liquid. The flow direction of the steam in the pressure chamber is essentially equal to the flow direction of the liquid jets. The plate is of plastic so as to have a low coefficient of thermal conductivity. Alternatively, the plate can have cooling channels to keep its upper surface desirably cooler than its under surface.