THE INFLUENCE OF CERTAIN MANUFACTURING PROCESSES ON THE STAPHYLOCOCCUS AUREUS CONTENT OF SPRAY-DRIED MILK

SUMMARY: Dried milk was prepared from milks inoculated with pure cultures of Staph. aureus , using a small pilot-type batch vacuum evaporator and spray drier. Vacuum evaporation reduced the numbers of Staph. aureus in most experiments but one strain was capable of multiplication at evaporating temperatures up to about 43°. Above 49° the organisms declined rapidly and at 56° they were eliminated. Residual staphylococci present in the warm concentrated milk feeding the drier increased in some experiments but declined markedly in others. Staphylococci added directly to warm concentrated milk always proliferated. A small proportion of staphylococci survived spray drying, even with high hot air temperatures. Different strains varied in their susceptibility to different stages of the whole process.