Abstract: Method and apparatus for heat treating a fluid product, in which the product is preheated in a countercurrent heat exchange process and heated to the desired treatment temperature in a throughflow heat exchange process, wherein in the primary countercurrent heat exchanger section, a higher pressure than the atmospheric pressure prevails, and both in normal operation and during recirculation through the final-temperature heating section, the secondary countercurrent heat exchange section is maintained at a higher pressure than the pressure in the primary countercurrent heat exchanger section, whilst, should the pressure difference between the primary and the secondary countercurrent heat exchanger sections drop out, the supply and discharge of the product are stopped and the product to be treated is recirculated through the final-temperature heating section.