Whole and skimmed milks were subjected to a range of high temperature short time treatments using a pilot scale plate heat exchanger. γ‐Glutamyl transpeptidase activity was assayed in the milks and the residual activities compared against the holding temperatures and total heat treatment. There was no residual activity following treatments of 78°C for 15 seconds, a total heat treatment 8.2 times more severe than that of a hold of 15 seconds at 72