The Application of Steam for Heating and Sterilizing Dairy Equipment

Abstract

Summary 1. Commercial applications of steam for sterilizing might be classified as first, steaming of cans over jets, second, steaming of cans in tank type containers, third, steaming by blowing a steam jet against the outside of the metal surface. 2. The most important properties of steam which affect its use as a sterilizing medium are as follows: a. Temperature of saturated steam increases with pressure. b. Temperature of steam at any given pressure may be raised by superheating. c. Superheated steam absorbs moisture. 3. Equations are developed which state that relationship between the factors involved in the thermal exchange which takes place when milk cans are steamed. 4. The heat absorbing capacity of a milk can is limited by the area of the surface, the coefficient of heat transfer, and the temperature difference between it and the heating medium. It is unnecessary to use any more steam than just enough to maintain the temperature of the heating medium inside the can, and to give the necessary turbulence, to insure a good coefficient of heat transfer. 5. Wet and saturated steam heated the cans at higher rates per degree difference in temperature between the can and the steam than did the superheated steam. Higher final temperatures of the can were obtained when superheated steam was used. 6. With a spreading type jet made by drilling a hole in a 1 2 inch pipe capacity, the temperature in the can metal varied about 14.6°F. after 15 seconds steaming, and varied about 5.7°F. at the end of a half minute steaming period. The hottest part of the can was near the junction of the sides and bottom. 7. Steaming with superheated steam left much less moisture in the can than when saturated or wet steam was used. 8. The use of superheated steam in the last steam jet of a continuous can washer assists in drying the cans. 9. The time-temperature curve showing the rate of temperature rise of milk cans when heated over steam jets, rises rapidly to a point where it flattens out sharply as the temperature is reached when there is equilibrium between heat supplied and heat radiated. 10. Milk cans when heated slowly in a steam heated tank type sterilizer, follow the sterilizer temperature closely. 11. Milk cans when heated slowly in a hot air heated tank type sterilizer, lag behind the temperature of the sterilizer to a considerable extent.