l8o MODERN METHODS OF TESTING MILK 



means milk containing- not less than 4 per cent, of fat 

 and not less than 9 per cent, of solids-not-fat. 



(2) Defective applies to milk containing less fat 

 or solids-not-fat than required for milk of "perfect" 

 composition. 



Keeping power is an expression used to indicate in 

 a general way the length of time milk remains sweet 

 and palatable for table use. 



Testing keeping power. — The keeping power of 

 milk is tested by making determinations of ( i ) the 

 acidity (pp. 88-100) (2) the dirt in suspension, (p. 

 109) (3) the fermentation test (p. 106) and, when 

 practicable, (4) the number of bacteria. 



Terms describing keeping power. — The terms used 

 in describing the keeping powxr of milk are (i) per- 

 fect, (2) acidity, (3) dirt in suspension, (4) undesira- 

 ble fermentations, and (5) number of bacteria per 

 cubic centimeter. 



(i) Perfect. — ^lilk is called perfect in respect to 

 its keeping power (a) when its acidity is not above .18 

 per cent, (b) when it contains no dirt in suspension, 

 (c) when the fermentation test reveals nothing ab- 

 normal, and (d) when the number of bacteria does 

 not exceed 100,000 per cubic centimeter. 



(2) Acidity is used to mean the amount of apparent 

 total acid calculated as lactic, as shown by the amount 

 of alkali neutralized. 



(3) Dirt in suspension is a self-explanatory expres- 

 sion. 



(4) Undesirable fermentations refer to the results 

 of the fermentation test. They may reveal themselves 

 in causing porous, spongy curd and in producing of- 

 fensive odors. 



