The present invention in a first aspect provides a method and a system for stripping volatile compounds such as ammonia from e.g. fermentation liquids. Part of the ammonia is stripped form the liquid in a stripper system comprising a shunt through which liquid such as e.g. fermentation medium comprising a biomass can be diverted in the form of a side stream in liquid contact with a main fermentor(s). The stripper system is connected to an evaporator. In the evaporator aqueous liquid is heated at a pressure below atmospheric pressure whereby vapour is developed at a temperature below 100°C. The vapour from the evaporator is directed to the liquid medium comprising ammonia and this results in ammonia being stripped from the liquid and transferred to the vapour phase. The vapour phase is condensed in first condenser at a low pressure, e.g. a pressure well below 1 bar, and the liquid thus obtained is further treated in a stripper unit at a higher pressure, such as e.g. a pressure at or above 1 bar, to obtain a more concentrated solution of ammonia. When stripped for at least part of the ammonia the liquid initially obtained from the biogas reactor and diverted to the shunt can be returned to the reactor.