Radio age research, manufacturing, communications, broadcasting, television (1941)

PASTEURIZING MILK BY RADIO By Subjecting Fluid to Higher Temperatures for Shorter Period, Electronics Lowers Bacteria Count and Preserves Flavor. PIONEERING in the develop- ment of radio heating proces- ses, members of the reasearch staff of EGA Laboratories, Princeton, N. J., have succeeded in extending the usefulness of this new applica- cation of radio energy to a remark- able number of industries. Success has been achieved in sewing, rivet- ing, welding, case-hardening and tempering; also in dehydrating vegetables, drying penicillin, puri- fication of cereals, pre-heating plas- tics and baking plywood planes and boats, among other distinctive ac- complishments. This new science of radiother- mics, a direct outgrowth of re- search in high frequency broadcast- ing, first received notice when it provided a means of speeding pro- duction lines during the war by completing in minutes industrial operations that had required hours or even days. Since then it has proved valuable in hastening output and reducing costs in peacetime manufacturing processes. Study of the problem of milk pasteurization was undertaken by George H. Brown, C. N. Hoyler and R. A. Bierwirth after contact with experienced dairymen who felt that the revolutionary possibilities of radio heat might bring solution to difficulties which had plagued the milk industry for many years. The investigation made use of previous experience, particularly that obtained at RCA Laboratories in applying radio-frequency heat- ing to dry food products such as cereals and flour for the purpose of purification and the destruction of weevils and weevil eggs. In com- parison with milk pasteurization, however, this process was simple and straightforward. Since the in- festing objects usually contain more moisture than the bulk of material, selective heating takes place and the mean temperature of the food package need not reach excessive values. For instance, ex- periments conducted at the Lab- oratories revealed that a mean tem- perature of 140°F was sufficient to completely inactivate weevils and eggs in one-pound packages of cereal. Long Treatment Affects Flavor On the other hand, in conven- tional pasteurization of milk, the milk is normally heated to a tem- perature of 143 °F and held at this temperature for 30 minutes. The milk is then cooled for storage or bottling with the bacteria content usually reduced to about 1 per cent of the starting value. Dairymen explained that if times less than 30 minutes are used the bacteria content is notably greater, whereas a longer time results in a cooked flavor and an apparent re- duction of cream volume. Investigation also was made of flash pasteurization methods in which the milk is heated to 161° F and held for 16 seconds. In some of these experiments the milk is spread on a thin film of heated plates and then quickly pumped over cooling plates. In another process the milk is passed between two electrodes to which 60-cycle voltage is applied. Since the milk is a good conductor, current flows EXPERIMENTAL PASTEURIZING SYSTEM ERECTED IN RCA LABORATORIES DURING RESEARCH ON THE ELECTRONIC TREAT- MENT OF MILK. through the milk and generates heat. It appears that difficulties with the electrodes have kept this latter method from becoming popular. Nevertheless, this method indicated the advisability of heating by means of electric current to explore the effects to be encountered with tem- peratures far in excess of 161°F. It was felt that the use of radio- frequency power might make pos- sible the heating of milk in continu- ous flow with the miUc coming in contact only with glass. Current Passes Through Milk Seeking to learn the solution of fundamental problems connected with this procedure, a series of experiments were carried out. In the first of these, milk was pre- heated to 140°F and was then run through a long glass tube, i/4" in diameter. Electrodes wrapped around the glass tube consisted of two pieces of copper foil, causing raido-frequency current to flow from one electrode through the glass to the milk stream and down the milk stream for a few inches. Temperature was measured by a thermocouple inserted below the second electrode. These experiments showed that excellent pasteurization could be obtained in about 67/1000 of a second though it was not possible to achieve temperatures above 190°F. The tendency above this tempera- ture was to form steam pockets with uneven flow. Study indicated that this tend- ency probably was due to non-uni- form flow in the tube, wherein the milk stream adjacent to the glass was slowed down by friction and thus raised to a higher temperature than the center of the stream. In efforts to circumvent this effect, the tube was so arranged as to produce a free-falling stream between the electrodes. With this arrangement, the milk could be heated to 205 °F without steaming or breaking. Using the uniform flow arrange- ment, experiments were conducted in which bacteriological tests were found to be excellent. The pre-heat- ing was accomplished by causing the milk to flow through tubing of (Continued on page SI) 16 RADIO AGE]