The invention relates to an installation for the continuous heat treatment of a heat-sensitive liquid, such as a dairy product. The inventive installation comprises: a mixing chamber (1) which is equipped with liquid and water vapour inlet means (2, 3) at which the liquid is subjected to a heat treatment under the effect of the heat supplied by the water vapour； a holding tube (5) having one end which is communicated with the mixing chamber (1) and one end which is provided with a cross-section-reducing means (7), such as to define a flow passage (18)； and an expansion chamber (8), the inlet of which is formed by the aforementioned passage (18). The installation is characterised in that it also comprises means for adjusting the cross-section of the flow passage.
