A MODEL HEAT-EXCHANGE APPARATUS FOR THE INVESTIGATION OF FOULING OF STAINLESS-STEEL SURFACES BY MILK .2. DEPOSITION OF FOULING MATERIAL AT 140-DEGREES-C, ITS ADHESION AND DEPTH PROFILING

Formation and adhesion of fouling deposit during heating of milk at a stainless steel surface were studied separately using a model apparatus. The amount of deposit and proportion of minerals present increased with increase in surface temperature. At 140 °C, the amount of deposit formed increased linearly with heating time, becoming more uneven in appearance. The variations of deposit formation at 140 °C with pH of the milk, with fat removal and with preheating were similar to those observed in the final heating section of continuous UHT plants. Deposits containing a higher proportion of protein were easier to remove. The remaining inner layer had a smoother appearance and contained a higher proportion of minerals than the original deposit. Depth profiling, using secondary ion mass spectrometry, showed that protein was concentrated on the outside of deposits with calcium phosphate being concentrated closest to the steel surface. © 1990, Proprietors of Journal of Dairy Research. All rights reserved.