Effect of homogenisation and preheat treatment of fresh, recombined and reconstituted whole milk on subsequent fouling of UHT sterilisation plant

There is ongoing debate in the literature as to whether preheating cows' milk lowers the rate of fouling in ultra-high temperature (UHT) heat exchangers. The effect on UHT fouling rates and characteristics of the foulant deposit of high and low preheat treatments of milk (95 °C, 147 s and 75 °C, 11 s, respectively) using pasteurised fresh whole milk (FWM), recombined whole milk (Rcb), and reconstituted whole milk (Recon), all prepared from the same raw milk batch, are compared. The fouling rates from FWM, Rcb and Recon markedly increased with application of the higher pre-treatment. These results held whether homogenisation was applied before or after preheat treatment for FWM, or for no homogenisation. It is speculated that the pasteurisation step has acted as a protein denaturation step, resulting in the additional preheating before UHT treatment making the milk supersaturated in minerals giving mineral-rich deposits in the UHT heat exchanger.