Investigations were undertaken at two small farm dairies noted to have sporadic failures of statutory phosphatase tests on samples
of cream. Bottled whole milkand skimmed milk from both dairies appeared to be satisfactory. Use of the highly sensitive
fluorimetric phosphatase test enabled us to demonstrate that diversion of heat-treated whole milkto a separator resulted in underpasteurisation.
This was due to increased flow rate through the holding tube and was confirmed by a simple timing experiment.
Modification of high-temperature-short-time pasteurisers in order to produce a range of products may affect the dynamics of flow
resulting in inadequate heat-treatment and possibly in survival of microbial pathogens.