788 EXPERIMENT STATION RECORD. 



Five series of experiments were made, each series including from 3 

 to 5 full-sized cheeses made from mixed milk under identical conditions. 

 These were cured at (1) a laboratory temperature, approximating 50° F. ; 

 (2) a normal curing-room temperature, ranging from 60 to 65°; and (3) 

 an abnormally high temperature, 85°. Bacteriological and chemical 

 examinations were made of the cheeses, the results of which are given : 



"Results of bacteriological analyses. — (1) It was found that the bacterial flora of 

 cheese cured at a low temperature (50 to 56° F.) retained for a certain period the 

 same general aspect as that of the milk. In cheese cured under ordinary conditions 

 there is almost immediately a differentiation as to the character of the micro-organ- 

 isms present, the lactic-acid type acquiring the ascendency. In the refrigerated 

 cheese this change is much less marked in the beginning, although it does occur in 

 the course of time. 



"(2) Bacterial growth in the cold cheese develops more slowly than at higher 

 temperatures and persists for a longer period of time. 



"(3) In cheese cured at a higher temperature the number of bacteria per gram is 

 greatly diminished when compared with either a refrigerator or normal temperature 

 cheese, and the bacteria fail to persist for as long a period of time. 



"(4) Not only is there a quantitative differentiation between cheese cured in low 

 and high temperatures, but a qualitative change is also more or less marked. In the 

 beginning of the ripening process the flora is practically the same, but in the cheese 

 cured at high temperatures there is a strong tendency toward differentiation when 

 compared with the flora of a refrigerator cheese. It is possible that this differen- 

 tiation in species may stand in close relation to the varying flavors of cheese cured 

 under these divers conditions, and further experiments on this point are in progress. 



"Results of chemical analyses. — (1) During the ordiuary life of the cheese, the rate 

 of curing changes is quite uniform, if the conditions are identical. Wheu reduced 

 to a curve it is apparent that it progresses somewhat more rapidly in the early stages 

 than later. 



"(2) The rate of the curing increases quite rapidly with a rise in temperature, 

 and within the limits of our experiment has been nearly proportional to the tem- 

 perature. Hence the cheeses cured at high temperatures were ready for consumption 

 much earlier than those kept at low temperatures." 



It was found in these investigations that cheese ripened faster (as 

 measured by the formation of soluble proteids) at a high than at a low 

 temperature, whereas the cheese cured at a high temperature contained 

 less bacteria than that kept in cold storage. In other words, where 

 the curing was most rapid there was a diminished bacteria content, a 

 relation which is thought to be contradictory to the theory that the 

 ripening of cheese is due exclusively to the action of micro-organisms, 

 but in harmony with the theory of the action of euzyms, "as the euzyms 

 naturally inherent in the milk would act much more rapidly at higher 

 temperatures than they would at a lower degree." 



The commercial value of the cold-storage cheese was rated by an 

 expert at 7§ cts., that cured at normal temperatures at about the same 

 price, while that cured at a high temperature "had a rank flavor and 

 a value not exceeding 3 or 4 cts. a pound." At that time prime Ched- 

 dar cheese was quoted at 7£ to 8 cts. The high temperatures impaired 

 both the flavor and texture, whereas the cheeses cured at 55° and 

 below were invariably of good quality and were entirely free from all 

 bitter flavor. 



