A method for operating a tube bundle heat exchanger for heating a temperature-sensitive concentrate of a food product under high-pressure with the tube bundle heat exchanger that has the following features: • at least one tube bundle (100.1) that consists of a number of parallel-connected inner tubes through which concentrate flows on the inside, • the inner tubes are annular, arranged on a single circle K, and are in each case braced at the end in a first and a second tube support plate (700, 800), • the inner tubes extend in the longitudinal direction of an outside channel (200*) formed as an annular gap through which a heating medium flows, • the inner tubes possess a common inlet designed in the form of a first connection opening that is in a first exchanger flange connected to the first tube support plate and is arranged centrally there, • the inner tubes possess a common outlet designed in the form of a second connection opening that is in a second exchanger flange connected to the second tube support plate and is arranged centrally there, • at least at the outlet side, the inner tubes fluidically terminate in a circumferential annular gap that is formed in the second tube support plate, and/or the second exchanger flange, • the circumferential annular gap is fluidically connected across an annular outlet-side channel to the second connection opening, • the annular outlet-side channel is bordered radially to the outside by the second exchanger flange, and radially to the inside by a displacement body that is arranged in an axially symmetrical manner on the second tube support plate, • the annular outlet-side channel has a specific extension length, and a specific length-dependent progression of its channel passage cross-sections (A s), characterized in that • the flow paths of the tube bundle heat exchanger impinged upon by the concentrate are designed so that the concentrate can be subjected to a pressure (p) up to a maximum of 350 bar, • a specific fluid mechanical shearing stress is generated on the concentrate that on the one hand tends to reduce and on the other hand standardizes the rise in viscosity, termed the gelling effect, in the concentrate, • when heating the concentrate in the inner tubes to generate the specific fluid mechanical shear stress, an elevated flow speed (v) of the concentrate is provided in the inner tubes, and/or • to generate the specific fluid mechanical shearing stress, an elevated flow speed (v) of the concentrate is provided in the annular outlet-side channel, and • the elevated flow speed (v) is max. 3 m/s. • at least one tube bundle (100.1) that consists of a number of parallel-connected inner tubes through which concentrate flows on the inside, • the inner tubes are annular, arranged on a single circle K, and are in each case braced at the end in a first and a second tube support plate (700, 800), • the inner tubes extend in the longitudinal direction of an outside channel (200*) formed as an annular gap through which a heating medium flows, • the inner tubes possess a common inlet designed in the form of a first connection opening that is in a first exchanger flange connected to the first tube support plate and is arranged centrally there, • the inner tubes possess a common outlet designed in the form of a second connection opening that is in a second exchanger flange connected to the second tube support plate and is arranged centrally there, • at least at the outlet side, the inner tubes fluidically terminate in a circumferential annular gap that is formed in the second tube support plate, and/or the second exchanger flange, • the circumferential annular gap is fluidically connected across an annular outlet-side channel to the second connection opening, • the annular outlet-side channel is bordered radially to the outside by the second exchanger flange, and radially to the inside by a displacement body that is arranged in an axially symmetrical manner on the second tube support plate, • the annular outlet-side channel has a specific extension length, and a specific length-dependent progression of its channel passage cross-sections (A s), • the flow paths of the tube bundle heat exchanger impinged upon by the concentrate are designed so that the concentrate can be subjected to a pressure (p) up to a maximum of 350 bar, • a specific fluid mechanical shearing stress is generated on the concentrate that on the one hand tends to reduce and on the other hand standardizes the rise in viscosity, termed the gelling effect, in the concentrate, • when heating the concentrate in the inner tubes to generate the specific fluid mechanical shear stress, an elevated flow speed (v) of the concentrate is provided in the inner tubes, and/or • to generate the specific fluid mechanical shearing stress, an elevated flow speed (v) of the concentrate is provided in the annular outlet-side channel, and • the elevated flow speed (v) is max. 3 m/s.