34 DAIRY LABORATORY GUIDE 



EXERCISE 13 



EFFECTS OF IMPURE WATER ON DAIRY PRODUCTS 



Object: To determine the effect of impure water upon 

 the quality of milk, when the water is added or used for 

 washing the utensils. 



Apparatus: Samples of fresh milk, four covered jars, 

 incubator, and thermometer. 



Steps: 1. Sterilize the glass jars by placing them in a 

 water bath; then gradually raise the water to a boiling tem- 

 perature. 



2. Remove the jars and invert them upon a clean surface 

 to cool. 



3. Fill jar No. 1 with milk for a check sample. 



4. Add 10 c. c. of impure water to jar No. 2; then fill with 

 milk. 



5. Fill jar No. 3 with milk, pasteurized at 145 F. for 

 fifteen minutes. 



6. Rinse jar No. 4 with impure water and then fill with 

 milk. 



7. Cover all the jars tightly; then set them into an incu- 

 bator and hold at 70 F. 



8. Examine at intervals and record all data. 







Application: 1. How do the odors and flavors of the 

 different lots compare? 



2. Which samples show the effect of impure water? 



3. How can the presence of objectionable odors and 

 flavors be accounted for in the various samples? 



