A laboratory technique using glass and stainless steel slides has been developed to study the build-up of milk film on hard surfaces and its removal with detergent-disinfectant mixtures. Soiling and cleansing treatments were of similar duration to those used in practice but were repeated 6 or 7 times a day for 4 days to simulate 12 or 14 days' milking and washing procedures in the farm dairy; no mechanical assistance was used with the cleaning solutions. Soiling was followed immediately by a pre-rinse, wash and final rinse, allowing a short period for drying before further re-soiling. The technique eventually developed involved treatments repeated 18 times, using solutions at 15·5 °C. The weight of milk film and its content of fat, mineral and ‘protein’ were determined.
Under the conditions of the experiments the following were observed.
(1) The deposit left by all treatments consisted mainly of fat with a smaller proportion of protein and still less of mineral matter.
(2) Glass accumulated slightly less deposit than did stainless steel with an aquablast finish.
(3) Removal of milk film was more complete when sodium hypochlorite was added to certain detergent solutions than when the materials were used separately.
(4) With the treatments studied, the use of the detergent solution from a previous treatment as a pre-rinse did not result in a reduction in the residual film.
(5) A final rinse with 0·1% phosphoric acid virtually eliminated the mineral matter from the residual film.
(6) The substitution of a warm (46°C) for a cold (15·5°C) pre-rinse resulted in a reduction of 40% in residual film and the further use of a warm final rinse effected a reduction of 64%.
(7) The addition of 0·05% wetting agent (Lissapol NDB, I.C.I. Ltd.) to the prerinse effected only marginal improvement in the treatments studied.
(8) Omission of the pre-rinse and corresponding lengthening of the detergent treatment had no consistent effect.