The supercritical water hydrolysis (SCWH) of biomass (P = 250 bara & T = 400 degrees C) allows directly obtaining sugars, which are high value products in the chemical industry, in reaction times lower than 0.2 s. The process is characterized by the high selectivity values which can be obtained controlling the reaction time. Reaction kinetics show that glucose degradation is only retarded at temperatures below 250 degrees C. Therefore, in the SCWH process, degradation control is achieved expanding the hydrolysis stream in a valve which instantaneously cools down the products. Although the selectivity values obtained are greater than 96%, the pressure is wasted on the valve expansion decreasing the global energetic efficiency of the process. In this paper a desuperheater designed in CFD which mixes the hydrolysis product with pressurized cooling water is presented. The temperature of the hydrolysis stream decreases below 250 degrees C in cooling times lower than 20 ms maintaining the selectivity value over 93%. Furthermore, the pressure remains at 250 bara increasing the global energetic efficiency of the process.