37 



contained in the milk, thus preFerving it from decomposition. Heating 

 at this temperature, while it kills or renders harmless the bacteria, does 

 not destroy the spores. This destruction of bacteria increases the keep- 

 ing quality of the milk or cream by several days. 



If it is desired to ripen cream for butter making by any special fer- 

 ment, the pasteurization of the cream, even for a few minutes, so over- 

 powers or partially destroys the ordinary bacteria of the cream that the 

 special bacteria introduced have opportunity to become thoroughly 

 developed. 



Sterilization of milk or cream means the heating of it to boiling or 

 even above the boiling point by aid of pressure. This not only des- 

 troys the bacteria, but the spores as well, although for a complete 

 destruction of the spores more than one heating is necessary. The so- 

 called Dahl process for making perfectly sterilized milk consists in 

 heating the milk to 158"^ F. for three quarters of an hour, then cooling to 

 104° F. for the same time, then heating to 175° F , and finally cooling 

 and placing in sterilized vessels. The object of heating to 104° F. and 

 holding at this temperature for three quarters of an hour is to allow the 

 sjjores, which were not destroyed by the first heating, to grow. The 

 second heating destroys them. Milk thus treated has been kept per- 

 fectly sweet for a long time 



Details to be observed in Pasltierizing. — The milk introduced into the 

 pasteurizing apparatus should be heated as rapidly as possible to 150° or 

 165° F. and held at that temperature from twenty to thirty minutes. 

 During the heating it should be constantly stirred, to prevent bxaming on 

 the sides of the vessel. At the expiration of the time the milk should be 

 rapidly cooled to 50° or GO-' F. and then drawn off into sterilized bottles 

 or cans, the covers put on at once, and placed in ice water. The bottles 

 can be cleaned by the use of some form of bottle cleaner now on the 

 market. This is to be preferred to the use of chemicals. After washing 

 they should be placed in boiling water for ten minutes, and then placed 

 upon racks, mouths downward, to drain. A better way is to use a 

 sterilizing oven (a jacketed oven surrounded by steam). The bottles 

 can be removed while warm from the oven, and immediately filled. 



Milk or cream thus treated will have but a slight cooked taste, and 

 this will almost entirely disappear in cooling. Its chemical composi- 

 tion is not changed, nor its digestibility decreased. It is claimed, on 

 good authority, that pasteurized cream will make a butter sui)erior to 

 that from unhealed cream. This is probably due to the fact that pasteur- 

 ization destroys obnoxious germs, and permits, by inoculation, the de- 

 velopment of those favorable to a good quality of butter. Fasteurization 

 causes both milk and cream to become thinner than the normal pro- 

 duets, with same percentage of fat. This diminished body is due to the 

 fact that the heat causes the fat globules, which are in clusters or clots., 

 to break apart and become more evenly divided throughout the milk. 

 P)abcock and Russell have overcome this by the addition of so-called 

 viscogen to the cream.* 



Viscogen is prepared by taking two and one-half parts by weight of 



* Bull. 54, Wisconsin Experiment Station. 



