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The Bacteriology of Swiss Cheese

IV. Effect of Temperature upon Bacterial Activity and Drainage in the Press

Research Laboratories, Bureau of Dairy Industry, United States Department of Agriculture

ABSTRACT

Temperature, pH, and bacterial counts were determined in Swiss cheese in the press at regular time intervals from dipping to 21 hours in samples taken at definite distances from the outer edge of the cheese. Results were obtained from studies of 55-pound laboratory cheeses and also from large factory cheeses. Moisture determinations were made on samples from the laboratory cheeses. The following conclusions were drawn from the results:

1. The area just beneath the rind cools more rapidly than the interior.
   
2. Bacterial growth and acid production correspond in general with" the decrease in temperature of each part of the cheese.
   
3. While all the starter bacteria begin to increase in numbers in the area 1 inch beneath the rind during the first few hours after dipping, the initiation of growth in the interior was shown to occur at the following intervals of time from dipping: S. thermophilus (C₃), within 2 or 3 hours; L. bulgaricus (Ga and 39aH), after 5 or 6 hours; and L. helveticus (39a), after 9 or 10 hours.
   
4. Essential functions of S. thermophilus in Swiss cheese in the press are the production of acid and the consequent facilitation of drainage from the interior of the cheese during the first 4 to 6 hours after dipping.
   
5. Large differences in pH between the interior and the area just beneath the rind result in insufficient drainage and high moisture content, and may tend to cause such defects as checking near the rind or a splitting of the curd known as "glass."
   
6. Bacterial content of cheese cloths was found not to influence the rate of acid production near the surface of the cheese.
   
7. Samples from the interior of the cheese, in order to yield results representative of the interior of the cheese, should be obtained at points at least 3 or 4 inches from the hoop edge.
   
8. A judicious use of starters promotes sufficient acid production throughout the cheese and thereby aids in uniform drainage.