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The Growth of Staphylococci in Condensed Skimmilk¹

Department of Dairy Husbandry, University of Minnesota, St. Paul

ABSTRACT

The following variables were studied from the standpoint of their effect on growth of staphylococci in condensed milk: (a) precondensing heat treatments, (b) milk solids concentrations, and (c) growth temperatures. Growth also was studied under conditions simulating vacuum-condensing operations.

Preheat treatment of skimmilk at 165 or 185° F. for 30 min. before condensing did not affect the growth of two cultures studied. However, growth of one of these cultures was retarded somewhat when the preheat treatment was 150° F. for 30 min.; growth of the other culture was not retarded.

Cultures of staphylococci grew optimally, or nearly so, at temperatures ranging from 90 to 113° F. in condensed skimmilks having solids concentrations ranging from approximately 30 to 50%. Three of six cultures grew, although slowly, in 40% milk solids at 116° F. and one grew under similar conditions at 118° F.

Under conditions of simulated vacuum condensing, growth was less extensive than under normal atmospheric pressure. However, growth was sufficiently rapid to exclude the possibility that subatmospheric pressures, likely to prevail in a vacuum-condensing operation, would afford sufficient retardation of growth to be of any practical significance in controlling growth of staphylococci.

¹ Paper No. 4063, Scientific Journal Series, Minnesota Agricultural Experiment Station. This study was supported in part by funds from the American Dry Milk Institute.