PHYSICAL AND CHEMICAL EXAMINATION OF MILK 207 



of a flask provided with a side tube in such manner that there can 

 be no air suction through the neck of the bottle. The pledget of 

 cotton is placed on the bottom of the crucible and moistened with 

 a few drops of water or milk to prevent slipping of the cotton. 

 The milk is then poured into the crucible and filtered through the 

 cotton. As the cotton soon clogs with fat, filtration is aided by 

 suction through the side arm of the flask (Fig. 80) . 



A convenient arrangement for making sediment tests is illus- 

 trated in Fig. 81. The apparatus is held by a telephone bracket, 

 and can be moved back and forth as desired. 



Test foe Viscosity 



The viscosity of milk can be measured by two simple meth- 

 ods. One of these consists in allowing a definite amount of 

 water to run from a pipet, and noting the time required to com- 

 pletely discharge the amount. Then the same amount of milk 

 is discharged from the same pipet, and the time required for com- 

 plete discharge compared with the time required by the water. 

 The second method consists in allowing a few drops of the milk or 

 cream to run down an incUned piece of glass, and measuring the 

 distance covered in a definite length of time. The following 

 table, which gives the variation of viscosity according to tem- 

 perature, may serve as standard: 



KELATION OF VISCOSITY OF MILK AND TEMPERATURE (REISCHAUER) 

 Temperature. Time required if water is 100. 



0°C 221 



5°C 208 



10° C 191 



15° C 189 



25° C 176 



30° C 169 



Testing Milk by Rennet 



The cheese maker is interested to know the exact degree of 

 ripeness at which to add rennet extract to the milk. The tests 

 designed to serve this purpose are based on the speed of rennet 

 action. Two tests are in practice, namely, the Monrad and the 

 Marschall tests. 



The Monrad Test. — Five c.c. of rennet extract of known 

 strength are placed in a 60-c.c. flask and the remains of the rennet 

 in the pipet washed with water into the same flask. The rennet is 

 then diluted with water to 50 c.c. and the contents mixed by shak- 

 ing. A graduated cylinder is filled to the 160 c.c. mark with the 

 milk to be tested and this is then emptied into an open vessel. 

 The temperature of the milk should be 30° C. (80° to 86° F.). 

 To the milk are then added 5 c.c. of the diluted rennet extract 



