Directly heating a protein-enriched milk product occurs by introducing steam, the direct heating taking the form of an infusion or injection method. The described technique significantly extends service time, ensuring a content of non-denatured whey proteins in the treated protein-enriched milk product greater than that obtained in the prior art. The milk product, which is preheated and kept at temperature is indirectly cooled before direct heating by a recuperative cooling step from the preheating temperature to a cool-down temperature with a temperature difference ranging from 5 K to 10 K. The direct heating from the cool-down temperature to the high pasteurization temperature is controlled by direct heating setting parameters which are known per se. Finally, the milk product is cooled by flash cooling from the high pasteurization temperature to a necessarily required exit temperature.