Heat-induced coagulation of concentrated skim milk heated by direct steam injection

Direct steam injection heat treatment on pilot scale was applied to investigate heat stability of concentrated skim milk across a broad range of temperatures from 117 °C to 153 °C and from 0.5 to 13 s holding time, assessing options for heat treat treatment without a significant amount of protein sediment formation. The relationship between total solids content of concentrated skim milk and temperature–time combinations of heat treatment could be established using minimal heat-induced coagulation as a criterion. Coagulation of destabilised casein micelles was shown to proceed non-linear over heating temperature. Transition of critical temperature–time combinations resulted in a marked increase in sediment formation indicating that preceding reactions, noticeable as the formation of dissociated material, need to take place to some extent to induce coagulum formation. UHT pre-heat treatment of skim milk prior to concentration was shown to increase heat stability in terms of possible temperature–time combinations without coagulation.