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The Bacteriology of Brick Cheese. III. The Bacteria Involved in Ripening¹

Department of Agricultural Bacteriology, University of Wisconsin, Madison

ABSTRACT

Examination of 1016 cultures isolated at different stages of ripening from 18 lots of Brick cheese yielded the following results:

1. Str. lactis was the predominant organism throughout the ripening of cheese in which it was used as part or all of the starter. Its numbers rose steadily to one to three billions per gram during the first one to four days, and declined again after three to four weeks. It also increased slowly in cheese to which it had not been added and reached numbers of several hundred millions per gram after one to two weeks.
   
2. When Str. thermophilus was used as the starter its numbers increased rapidly to a maximum of one to two billions per gram at twelve hours, then after one to two weeks they decreased sharply and the organisms seldom were found later in the ripening period.
   
3. Lactobacilli were found in the raw milk cheese after the first one or two weeks, but they seldom appeared in cheese made from pasteurized milk. L. casei occurred most frequently and in numbers up to ten to one hundred millions per gram; L. irevis was found less consistently than L. casei and usually in much smaller numbers; L. lactis appeared in a few of the samples after three to four weeks in insignificant numbers.
   
4. Str. liquefaciens was found in six of the lots of cheese after two to three weeks in numbers sometimes as high as 10,000,000 per gram. A few instances of bitter flavor probably were due to excessive numbers of this organism.
   
5. Str. bovis and Str. fecalis usually appeared in the cheese after one to two weeks, and ranged in numbers from a few thousands to as high as one hundred millions per gram. These organisms were most prevalent in cheese made from pasteurized milk.
   
6. Late gas formation by anaerobic spore forming bacteria occurred in all cheese in which the pH did not drop below 5.3 during the first three days of ripening. This condition was most pronounced in cheese made with Str.thermophilus starter by the washed-curd method from pasteurized milk. The main function of the starter bacteria is a rapid and steady production of lactic acid during manufacture. The most important organism in bringing about the changes in body within the cheese during ripening is L. casei, and this organism also contributes to the flavor.
   

¹ Published with the permission of the Director of the Wisconsin Experiment Station.

² Now in the Department of Botany and Bacteriology, University of Texas, Austin.

³ Now in the Department of Bacteriology, University of Illinois, Urbana.