Page:Foods and their adulteration; origin, manufacture, and composition of food products; description of common adulterations, food standards, and national food laws and regulations (IA foodstheiradulte02wile).pdf/246

 the number of organisms decreases. At first the decrease is very rapid and then becomes slower as the cheese becomes riper. The decrease in the number of bacteria when the temperature of curing is raised is somewhat contrary to expectations. It has been found that when a cheese is taken from cold storage, say at 24 degrees F., and placed in a temperature of 60 degrees F., the decline in the number of bacteria is always greater than when the cheese is retained at the lower temperature. This may be due to the fact that bacteria which have been developed at a low may lose their vitality at a higher temperature. On the contrary, the development of flavor does not seem to depend upon the number of organisms since the peculiar flavor of cheese is more rapidly developed at the higher temperature, provided it be not too high, although this be attended with a diminution in the number of organisms. Evidently the conditions which favor the metabolic activities of organisms also favor their destruction, since when they have performed their functions they undergo natural disintegration. The character of cheese is such that when it is once formed there is no more opportunity given for a rapid proliferation of the organisms.

It may be found, however, that the development of bacterial life is not the sole or perhaps not the dominant factor in the development of flavors and aromas in cheeses but that this process is due very largely to the enzymic activities obtained from the rennet and which pre-exist in the milk.

Chemical Changes Which Take Place During the Ripening of the Cheese.—Loss of Weight.—During the process of ripening of cheese there is considerable loss of weight, amounting to from 15 to 20 percent of the total weight of the fresh product. This loss is due chiefly to the evaporation of water, while in the fermentation which takes place volatile bodies are formed which also escape with the water. For instance, any free gas, either carbon dioxid, hydrogen, or nitrogen, which is produced will escape, likewise any alcohol which is formed will at least partially volatilize. There may be also a slight loss due to mechanical attrition, but that is not of any consequence. Owing to the loss of water some of the constituents which may diminish in actual quantity have their percentages proportionately increased. These changes are illustrated by the following analytical data:

Fresh cheese,                 40.42   24.80     28      1.65         5.43 In the dry substance,                 41.62     46.99 Same cheese one year old,     33.12   27.35     31.70   2.96         4.87 In the dry substance,                 40.89     47.40

The quantity of water which is lost in part depends upon the temperature of the store house and the dryness of the air. The loss of water should not be too great, otherwise the cheese would be dry and the ripening process would not go on in a proper manner. In some of the processes which take place