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Comparison of Standard Methods of Measuring Holding Time in H.T.S.T. Pasteurizers

Department of Dairy Industry, Cornell University, Ithaca, New York

ABSTRACT

Three tests for the determination of holding time were compared; namely, the nickel chloride—dimethylglyoxime chemical method, the sodium nitrite—Griess-Ilosvay chemical method, and the salt conductivity method. Tests were carried out, under field conditions, on five commercial plate-type, high-temperature, short-time pasteurizers, the capacities of which ranged from 3,935 to 16,525 lb. per hour. The size of holding tubes on these units was from 1- to 2-in. nominal size sanitary piping, whereas one of the units had a plate-type holder section.

The methods were compared under conditions as nearly identical as circumstances would permit. Results of tests, carried out in accordance with these methods, were compared on the basis of the same flow rate, with the same type of injection being used. The point of injection of the solution used as a tracer was the same in all tests in relation to the flow of liquid entering the holding section.

The results indicate that the sodium nitrite test was more sensitive as a method of determining holding time than either the nickel chloride test or the salt conductivity test. This was more apparent in high-capacity units, using larger-sized holding tubes, and in lower-capacity units with a low holding-tube efficiency. The nickel chloride test and the salt conductivity test were shown to be of comparable sensitivity on low- and medium-capacity units, but on higher-capacity units the nickel chloride test appeared more sensitive than the salt conductivity test.

¹ Present address: The West of Scotland Agricultural College, Auchincruive, Ayr, Scotland.