298 CITY MILK SUPPLY 



occurred of a cream, with a trifle higher acidity than usual, giving on 

 pasteurization a thin layer of free fat and imparting a granular feel to the 

 tongue. 



Bottling Milk Hot. With regard to bottling milk hot Ayres and 

 Johnson concluded that as good or even better bacterial reductions can be 

 obtained than when the milk is pasteurized in the bottle. Bottle infec- 

 tion is eliminated, even when several cubic centimeters of old sour milk are 

 added to the bottles before filling them. The 2-min. steaming that 

 bottles receive before being filled with hot milk destroys the contamina- 

 tion. Laboratory experiments indicate that milk may be pasteurized, 

 bottled hot, capped with ordinary cardboard caps and cooled with a cold 

 air blast. It is probable that if milk is cooled from 145F. to 50F. within 

 5 hr. no greater bacterial increase will take place than if it is cooled at once 

 to 50F. Future experiments will be necessary to determine whether 

 this will be true under commercial conditions. So far as laboratory ex- 

 periments show, milk that is heated to 145F. for 30 min. and bottled hot, 

 when subjected to slow gradual cooling through periods of less than 5 hr. 

 duration, is liable to no more trouble with the cream line and with off 

 flavors than is milk pasteurized and cooled in the usual way. A quart of 

 milk in cooling from 145 to 50F. shrinks about 0.62 oz.; so slightly 

 oversized bottles should be used for bottling milk hot. 



Difficulties Encountered in Pasteurization. In commercial pasteur- 

 ization difficulties of different sorts are encountered. Milk occasionally 

 coagulates in the pasteurizing apparatus. Harding and Rogers state 

 that it has been found impractical to pasteurize milk intended for im- 

 mediate consumption when the acidity is over 0.2 per cent, calculated as 

 lactic acid, and in the course of their experiments on the efficiency of a 

 continuous pasteurizer, having a steam-heated jacket, they found that as 

 the acidity approached 0.36 per cent, a considerable layer burned fast 

 to the sides of the milk chamber of the pasteurizer and the accumulation 

 in the separator bowl was increased. The question was studied by Kastle 

 who concluded from his own results and those of others that the coagu- 

 lation of milk is dependent on several factors among which are: time, 

 temperature, degree of acidity, quantity and nature of the calcium salts, 

 etc.; and that in order to avoid accidents resulting from curdling in the 

 pasteurization of milk, the only safe rule to follow is to determine the 

 effect of heat on small samples of milk which it is proposed to pasteurize. 



A cooked flavor is noticed by many consumers in milk heated to 158F. 

 It is probably due to the effect of heat on the milk sugar and may be 

 avoided by the use of low temperatures in pasteurization. 



Much trouble has been experienced from the fact that pasteurized 

 milk may have an ill-defined cream line and may show shrinkage in the 

 volume of cream that rises to the top of the container. The accepted 

 explanation of this fact has been that in raw milk the fat is in clusters 



