is fed to the mixing zone through a conduit 2 and steam is provided through conduit 3 the steam is introduced in an amount corresponding to the maximum temperature at which it is desired to heat the liquid adjusted to compensate heat loss in the equipment the steam may be superheated but typically its temperature is only little above the saturation temperature or at the saturation temperature it is an essential feature of the method according to the invention that the amount of steam introduced through 3 is in excess of the minimum amount required to obtain the desired heating that means the amount of steam introduced is higher than the amount which condenses by contacting the liquid in the embodiment depicted the liquid after being heated and diluted by the water created by steam condensation therein passes into a pipe 4 which together with the exit part of the equipment forming the mixing zone 1 constitutes a holding or retention zone also the non condensed portion of the steam introduced through 3 passes from the mixing zone into the holding zone in pipe 4 the liquid as well as the surplus of steam leaves the pipe 4 through a valve 5 in a preferred embodiment this.