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The Bacteriology of Swiss Cheese. II. Bacteriology of the Cheese in the Press

Research Laboratories, Bureau of Dairy Industry, U. S. Department of Agriculture, Washington, D. C.

ABSTRACT

A study has been made of the bacteriology of Swiss cheese from the time the curd was dipped from the kettle until 21 hours later.

Small cheeses with a green weight of about 55 pounds were used in most of the experiments, but results have been compared to those with large cheeses.

A summary of results showed:

S. thermophilus usually started to grow within three or four hours after dipping and increased in numbers rapidly until the sixth or eighth hour. Thereafter the increase in numbers was slow and in some cases the numbers decreased gradually until the twenty-first hour.

L. helveticus (39a) usually decreased slowly in numbers until about the sixth to eighth hour in the press and then increased at a fairly rapid rate. The numbers after 21 hours were high with an active starter and low with a weak one.

L. bulgaricus (Ga) usually decreased in numbers until about the fifthhour after dipping when a rapid increase in numbers took place.

The pH of the cheese usually dropped more rapidly during the first seven or eight hours than during the later hours. This early drop in pH evidently was due chiefly to the action of the S. thermophilus organisms present. Most of the cells of S.thermophilus had a diameter 3 or 4 times and a volume approximately 27 or 64 times as great as that of cells grown at ordinary temperatures. This is one explanation for the large fermentative activity per cell during the first hours' of the cheese in the press. Moreover, small amounts of acid can produce relatively large changes in pH during the early hours in the press, since the buffer value is relatively 'small in the early pH range.

The pH of the cheese at three and at twenty-one hours after dipping may serve as an indication of the effectiveness of the S. thermophilus and lactobacillus starters, respectively. The relative change in pH is more significant than the actual pH value.

The action of S. thermophilus is about the same in large cheeses as in small, but the growth and action of the lactobacillus cultures usually begin an hour or two later in the larger cheeses, because the interior cools more slowly than in smaller cheeses.

Gas formation and growth by either Escherichia communior or Aerobacter aerogenes can be suppressed in cheese in the press by use of active starters. If A. aerogenes has been present in large numbers in the kettle contents, however, a poor quality cheese will probably result.

Propionibacterium shermanii did not grow in cheese in the press. Bacteria of the tetracoccus or Lactobacillus casei types usually increased in numbers, if present, and under some conditions attained large numbers by the twenty-first hour.

C. lactis died off rapidly in cheese in the press. Organisms of the Lactobacillus lactis and Lactobacillus longus types were able to grow rapidly but usually were not present in large numbers.