Apparatus comprises at the product output of the pasteurizer a temp. gauge, the first output of which is connected to the input of a secondary converter, while its 2nd output is connected to a first control unit. The output of the latter is connected to a regulating valve at the input into the pasteurizer of an energy carrier stream. Design features to increase productivity of the pasteurizer during adverse internal disturbances include a 2nd control unit, the input of which is connected to the output of a primary converter. The pasteurizers may be for dairy products or beer.