16 DAIRY LABORATORY GUIDE 



EXERCISE 5 



THE SOURCE OF FERMENTATIONS IN DAIRY PRODUCTS 



Object: To note the effects of undesirable fermentations 

 in milk and to determine their source by means of the Wiscon- 

 sin curd test. 



Apparatus: Samples of milk, pint jars with covers, 

 rennet, extract, thermometer, knife, and warming tank. 



Steps: 1. Number the jars and sterilize them thor- 

 oughly. 



2. Fill each jar about half full of the milk and then place 

 them in the water bath. 



3. Heat the water until the samples reach a temperature 

 of 100 degrees F.; then add ten drops of rennet to each and 

 mix thoroughly. 



4. After the milk has curdled, allow it to stand for a few 

 minutes and settle; then cut into small pieces and drain off 

 the whey. 



5. Cover the j ars and replace them in the bath for several 

 hours at the regular temperature. 



6. Examine the samples for odor, flavor, and appearance 

 of curd at short intervals for several hours; then allow to 

 stand for a few days and reexamine. 



7. Care is necessary in every detail of this test to keep 

 the temperature of the samples uniform and to prevent con- 

 tamination. 



Application : 1. How do the samples of milk differ as to 

 appearance of curd? 



2. How do the appearance of the curd and the char- 

 acter of its flavor correspond? 



3. To what are pin holes due? 



