Contamination of Milk. 39 



tained, because, it has resulted in such an improvement 

 of the cheese that the gain was much greater than the 

 cost, which is estimated at not over fifty cents per ton of 

 cheese. The whey is heated not to exceed 155 F. ; the 

 hot whey serves to scald the whey tank and as the mass 

 of whey is usually quite large, it does not cool to a point 

 where bacterial growth can take place for a number of 

 hours. The whey is thus quite sweet when returned to 

 the farm and has greater feeding value. The heating 

 also prevents the creaming of the whey in the tank and 

 thus avoids the soiling of the cans with grease which is 

 most difficult to remove. 



Where compulsory legislation is in force it is gener- 

 ally required that these by-products be heated to a tem- 

 perature of at least 176 F. This is. done so as to destroy 

 effectually the organisms of tuberculosis, and especially 

 to permit of the utilization of the so-called Storch test, 1 

 which enables a person to determine quickly whether 

 milk or whey has been heated or not. 



Cleaning utensils. Various processes are applied to 

 dairy utensils to cleanse them. In removing visible dirt 

 and foreign matter, much of the bacterial life is mechan- 



i Storch (40 Kept. Expt. Stat, Copenhagen, 1898) has de- 

 vised a test whereby it can be determined whether this treat- 

 ment has been carried out or not; milk contains a soluble 

 enzyme known as peroxidase which has the property of de- 

 composing hydrogen peroxid. If milk 'is heated to 176 F., 

 (80 C.) or above, this enzyme is destroyed, so that the above 

 reaction no longer takes place. If potassium iodid and starch 

 are added to unheated milk and the same treated with hydro- 

 gen peroxid, the decomposition of the latter agent releases 

 oxygen which acts on the potassium salt, which in turn gives 

 oft' free iodine that turns the starch blue. 



