The flash pasteurization system is designed to pasteurize the product gently without adversely affecting its colour, taste or digestibility. For optimum results, pasteurization time, temperature and pressure have to be individually adjusted. Optimum parameters depend on various factors, such as product, type of packaging and anticipated shelf life. Based on highly accurate process control, the unit guarantees constant pasteurization quality even at variable product flow directly in front of the filler. To increase the energy efficiency of the system, the product is warmed up to the pasteurization temperature in two steps. In the first step it is heated in a heat recovery section where it flows in counter current to the hot, already pasteurized product. In the second step it is gently brought to the pasteurization temperature by the heating medium, e. g. hot water, heated by steam. If the flash pasteurization system is installed directly in front of the filling machine, it can compensate for variations of product quantity picked up by the filler. CIP cleaning of the unit can take place as the same time as the main line or separately.