Bacteriophage was used to induce starter failure in 12 batches of Cheddar cheese produced from milk inoculated with Staphylococcus aureus. At the end of cheddaring, only half the curd of every batch was salted and each curd portion was pressed separately. These cheeses were then stored at 4 C and also at a cheese maturation temperature of 11 C. Changes in the count of S. aureus, the associative growth of other microorganisms, pH, organoleptic properties and enterotoxin A concentration during production and storage were monitored. The data indicated that, in cheese without starter activity, inhibition of growth of S. aureus and enterotoxin production may be achieved during production by not salting the curd at the end of cheddaring, avoiding pressing at high ambient temperatures and minimizing the pressing time of the curd. Storage of salted cheese at 11 C appears to be a potential hazard because of significant increases in S. aureus count and enterotoxin concentration. When unsalted cheese was stored at 11 C, the count of S. aureus decreased and no change was observed in enterotoxin concentration; however, serious flavor deterioration occurred after 2 weeks. At 4 C, the S. aureus count decreased at a higher rate in unsalted cheese as compared with salted cheese, and in both instances there was no change in enterotoxin concentration.
1Present address: Australian Dairy Corporation, Melbourne, Victoria.