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The Use of a Direct Reading pH Meter for Routine Examination of Milk at the Dairy Plant Intake^*

Pennsylvania Agricultural Experiment Station

ABSTRACT

Many dairy plants use certain, so called, "quick quality tests" to determine the acceptability of milk delivered to their receiving rooms from dairy farms. Perhaps the most commonly used test is the "acid grading" test which determines whether milk is above or below a previously selected acidity level, often 0.18 per cent. Another common test is the alcohol test which classes as inferior any milk exhibiting flocculation when mixed with an equal volume of alcohol, usually about 70 per cent by volume. The prevailing belief among the users of these tests is that they will detect milk which has undergone bacterial fermentation or milk which has been affected by mastitis infections of the udder and which would otherwise escape notice. It is well known that these tests are not particularly accurate for the purpose intended and the proportion of borderline cases and false judgments is relatively large. Nevertheless their use continues, possibly because they are easily made, the results are immediately available and they do not interfere with nor retard the efficient handling of the milk at the intake.

^* Authorized for publication on August 24, 1942, as paper No. 1121 in the Journal Series of the Pennsylvania Agricultural Experiment Station.