Inhibitory factors in cheese milk

Abstract

Some milks were found to be inhibitory to one group of starters when tested by a 6 1/2 hour activity test, but the phenomenon was not evident when the same milk was tested by a 6 1/2 hour vitality test in which the milk is clotted with rennet. Comparison of these tests with actual vat workings at a commercial cheese factory showed that the results of vitality testing correlate well with acidity production in the vat. In contrast, the results obtained from the activity test are markedly affected by inhibitory factors in the milk and show no correlation whatever with vat workings, It is concluded that the activity test in pasteurized milk is a very unreliable measure of the ability of starter strains to work satisfactorily in the cheese vat and that the vitality test should be used for this purpose.