2112 I'ASTi:URlZATI()X 



into a tcil-tuljL* and onL- (ir two drops vi a 0.2 per cent solution of 

 h\TlroLcen peroxide i> added from a drojjpinL: bottle, also two 

 dr(jps of a 2 jier cent solution of paraphenylenc diamine, from a 

 dropping bottle. Brown drojiping bottles should be used to 

 preA'cnt the light from weakenini; the reagents. The test-tube 

 is then well shaken, and if the milk has n(jt been heated above 

 7S' Cor 172' F., or if not heated at all, an intense blue coloration 

 is produced. If at once or after half a minute the milk becomes 

 bluish-grc}', it indicates that it ha^ been heated to a temperature 

 of jS" C. to So" C. or 172" F. to 176^ F. ^^'hen the color of the 

 milk is unchanged after addition of the reagents, it may be 

 concluded that the heating has exceeded So' C. The blue color 

 that de\"elops on stanflinghas no significance. 



Storch's test has shown itself to be the most reliable of all the 

 methods projjosed for distinguishing heated from unheated 

 milk. All the so-called improvements which have been ad^"0- 

 cated b}' other chemists have proven to be of no benefit, often 

 indeed the opposite. 



If during the jiasteurization of the milk the temperature falls 

 below So"' C. for a time, the whole of the milk after being mixed 

 reacts to Storch's test. The sensibilit}' of the test is so great 

 that the admixture of 10 per cent of milk which has only been 

 heated to 7S" C suffices to make the whole ^-olume of milk react 

 to the test. 



Pasteurization Temperatures. — In pasteurizing or heating 

 milk for city trade or imm.ecliate consumption, low temperatures 

 are u?ed. This is done for the purpose of a^■oiding a cooked or 

 heated taste. The method found n:ost satisfactory fcir milk is 

 to heat to 145" ¥.. and hold at this temperature for twenty 

 minutes. This is known to the trade as the holding method. 



Where the flash or instantane(.)us method is used, the nrilk or 

 cream is heated to a temperature of 175^ to ico° F. The tem- 

 peratures most commonl}" used in butter-making in creameries 

 are iSo to 185' F. Of late }'ears the liigher tem.jieratures have 

 been used for butter-making, e^ en in the holding method. 



iNIarker. in the Canadian Northwest, recc^mmends heating to 

 170 or 175' F.. and holding for fifteen or twenty minutes. This 



