The invention concerns a process for the treatment of heat-sensative fluid food products (P) in a UHT system (1), particularly dairy such as milk, cream, milk protein concentrate. The invention has the task, in a UHT system whose basic structure using an infusion chamber is described in [4], of ensuring an equal and constant dwell time as well as an equal and constant temperature trend for the entire treated food product downstream of an outlet of a mechanism in which the food product is subjected to direct heating by the introduction of steam, and to minimize fouling during heat maintenance of the food product in this area. This is achieved using process technology in that: The heated food product (P*) upstream of its heat main undergoes a predetermined pressure increase (Δp) at a predetermined, unchanging location, and The pressure level upstream of the location before the relief lies above the pressure upstream of the location before the pressure increase (Δp) (FIG. 1).