Direct and indirect heating of milk-A technological perspective beyond time-temperature profiles

Indirect and direct heating are common technologies used in the dairy industry especially for UHT milk. Often direct heating is chosen to keep sensitive ingredients more intact while ensuring sufficient microbial inactivation as a result of its 'shorter and higher' time-temperature profile. A view on the technical principles of these processes exposes further differences, resulting namely from mixing of product and steam, hydrodynamic forces, removal of gasses and volatiles, product dilution and fouling. The implications of these on design of processing units and their impact on milk constituents is discussed along with the gaps. (c) 2021 Elsevier Ltd. All rights reserved.