Study of Dairy Cleaning Problems I. Films and Deposits on Hot-Milk Equipment

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Abstract
The removal of films or deposits from dairy equipment used in the heating and holding of milk products often presents a serious problem. Parker and Johnson (1) early directed attention to the practical and sci- entific aspects of this problem. They defined milk film as the deposit which forms on metal heat-transfer surfaces due to the precipitating action of the heat alone. Milkstone was defined as the product resulting from the reaction between the milk film as described and the chemical constituents of the water supply and alkaline detergents applied or their end products. In commercial operations where milk products are heated, particularly above 140 ° F., by metal heat-transfer surfaces, there appears to be a daily film formation of some extent depending on the thermM differential and the type of equipment. This may vary from an extremely thin, trans- parent or translucent film appearing as a bluish or brown discoloration when viewed from an angle, on heater plates or tubes, to a heavy cheese- like blanket of milk solids on batch pasteurizing vats in which relatively rapid heating is accomplished by means of a high jacket temperature. Before an effort was made to determine the most suitable detergents or cleaning methods for hot-milk equipment, it was deemed advisable to study further the mechanism of the film formation on metal heat-transfer surfaces and to account, if possible, for some of the differences observed. EXPERIMENTS A simple apparatus was devised by means of which milk could be heated continuously under controlled conditions. The apparatus consisted of a 9-inch length of 2-inch stainless steel tubing stoppered on both ends with rubber stoppers. One stopper contained inlet and outlet tubes of 5 ram. I. D. glass tubing and a thermometer, of which only the bulb was extended on the inside. The inlet tube extended to within one inch of the bottom stopper. The outlet tube was flush with the inner surface of the top-retaining stopper. This assembly was placed vertically in an agi- tated, gas-heated water bath. The raw milk of 4 per cent fat content, fore- warmed to 85 ° F., was allowed to flow through the tube by gravity, being drawn off at the desired temperature through regulating the flow by means of a stop-cock on the inlet tube.

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