PASTEURISING MILK.

Wairarapa Age, 21 March 1929, Page 6

PASTEURISING MILK.

Up-To-Date Method i THE USE -OF ELECTRICITY. HISTORY AND ADVANTAGES. The steady advance of electrical piocesses in the realm of p.<’'lotion was attested at the Science Congress at Auckland lately, when Dr. I’11. MeDowall, of Massey College, prc-| sented. a paper m which he the 1 uses of electricity in thu pasteurisation of milk. Pasteurisating has beeir a common practice for many years in the various branches of the dairy industry, but, almost without exception, the source of heat has been steam, generated, from coal. It. is only within recent years, says Dr. MeDowall, that an apparatus has been developed;, making possible the use of electrical energy for this purpose. Experiments were begun by Beattie and Lewis at Liverpool, England, in 2911, on the use of electricity directly for pasteurisation by passage of the electrical current through the milk They found it necessary to use high voltage alternating current, and assist ed the pasteurisation effect, in part at least, to the action of the electrical current on the micro-organism presentBeattie and Lewis did not develop their apparatus much, past the experimental stage. Their work had, however, been continued in Holland and America, and there were now two tvpes of electro-pasteurisers available for commercial purposes. DESCRIPTION OF DUTCH PLANT

The Dutch apparatus (eleetinopasteur) 1 follows more or less closely the design of Beattie and Lewis, states Dr. MacDowalL Three phase alternating current is transferred from the town supply to a voltage of 4000, and connected to the electrodes of the pasteuriser which are joined to the ends of a series of glass tubes arranged in the shape of a IT. The pa-sage of the elec trical current through the nfilk generates heat, resulting in a progressive ’ rise in temperature a<s the milk passes 1 through the tubes. The hot pasteuris- 1 cd milk is used to forewarm, the /»old ! milk before it enters the pasteuriser. ‘ The temperature of pasteurisation : . can be altered by variation of the ■ speed of flow .->£ the milk. Whch the 1 apparatus has been ®nt to deliver milk J at a certain temperature, no further ( attention is required, since automatic i devices are fitted in order to keep the j pasteurisation temperature constant. j The apparatus can be made with capacities up to 4000 gallons per hour, at a co.,t c f about £7OO. The American electric pasteuriser, “ elect ropure,” was much sin.pier than those of Beattie and Lewis in England, and of Aten and Straub in Holland. Electric current was used from the town supply at 230 volts A.C., being passed transversely to the stream J of milk in a rectangular cell two large slabs of graphite which act J as two ends of the cell, and as electrod-1 es. The electrodes were held apart by ( two slabs of slate rrhieh formed the remaining two sides of the coll. A re-: generative system was employed, and 1 the temperature of the pasteurised rniJk ; was automatically kept constant by a ’ special device controlling the speed of the milk pump. The capacity of on** unit was 600 .gallons pe<r hour. ' The American process uses temperatures (160-165 F than the Dutch process. It was being used quite extensively in America for the treatment of milk in city milk supply' plants. One large dairy dealing with ' more than half the milk supply of littshurgh had intsalled <six units, ■ capab'e ■ o« dealing with 3600 gallons P« r Hour. practicability nr ZEALAND The costs of pasteurisation by both the “ electTopasteur'' and the "electropure" were eotu'i«ierably higher than by the ordinary steam methods, bun actual figures were available show'.ng the cost of pasteurisation by steam, but it could be safely admitted that the treatment of 1000 gallons of milk world be seven to ten times as costly in New Zealand if the electropasteur were used, and about three times as costly, by the electropurc process, electric power costs being taken at Id per k.w.h.

The cost of treatment by the elec-tro-pasteur process was therefore prohibitive although alternations in design may reduce such costs very considerably. For a city milk plant the electropurc process had many advantages which might out-weagh the extra cost of treatment, which amotuted to less than l-12d per gallon. The space re- 1 quirements were smaller than for the ordinary pasteuriser, the automatic control reduced the labour requirements, and the cleansing operations were very simple. “New Zealand i-s just at the beginning of her development of city dairies supplying carefully treated " bottled milk, for household purposes," concluded the doctor. “In view of the cheapness of electrical energy, it is possible that the ‘ electropure ’ process may find an extensive use here. For cheese factory purposes the apparatus has the ■lisadvantage of small capacity and higher cost. It® automatic control of temperature would be a great advant|age.M