Fig. 136. Types of milk pails 



EXERCISE 83 

 METHODS OF PRODUCING SANITARY MILK 



Statement. The souring of milk is due to the growth of bacteria in the milk. The more numerous 

 the bacteria in the milk the more rapidly it sours. Bacteria which sour milk are not generally present 

 in the milk before it is taken from the cow, but enter the milk in dirt, from the air, etc. There should 

 be as little dust as possible in the air of the barn at milking time, and no dirt should be permitted to ' 

 gain access to the pail. 



Object. To determine some of the factors which influence the keeping quality of milk. 



Materials. Cows which the pupils may milk; open and covered milk pails ; place for cooling milk; 

 a number of one-half-pint bottles. 



Directions. 1 . Milk one cow, using for the milk container an open pail. Milk another, using a partly 

 closed pail. Have both pails sterilized immediately before using them. At once take samples of milk 



from each pail, keeping the samples in clean, sterilized milk 

 bottles, well sealed. Place the two samples under the same con- 

 ditions of heat and light. Observe the results. 



2. Let sour milk stand for a while in each of two milk 

 bottles. Later wash one bottle and sterilize it with boiling 

 water. Drain the water and do not dry with a cloth. Pour 

 the milk out of the other bottle but do not wash it. Fill the 

 two bottles with fresh milk from the same pail, seal and , set 

 aside under the same conditions. Observe results. 



3. Obtain two samples of fresh milk; cool one sample im- 

 The pail irthekft is Xbett e rTecauIe the hood mediately after milking and leave the other sample to cool 



helps to keep the dirt out of the milk gradually at room temperature. Otherwise, keep the samples 



under the same conditions and observe results as to the rate at which each sours. 

 At the end of twelve hours, observe each sample taken above as follows : 



a. Taste each sample and record whether it is sweet or sour to the taste. 



b. Place a definite portion (20 cubic centimeters) of each sample in a white dish and add phenol- 

 phthalein solution, drop by drop from a burette, with constant stirring. Note and record the number 

 of cubic centimeters of solution added before the milk changed color. Since phenolphthalein solution 

 turns red in the presence of acid, this test tells which milk is the sourer. 



Questions. How do bacteria gain access to milk ? Mention several methods by which the number of 

 bacteria in milk may be lessened. Does cooling milk at once after milking decrease the number of 

 bacteria entering the milk or does it decrease the rapidity with which they multiply? Might dirty 

 milk be kept sweet for a reasonable length of time if kept at a low temperature ? How should milking 

 utensils be treated to keep them clean and also free from bacteria? How may dirt largely be prevented 

 from gaining access to milk? What precautions should the dairyman take with regard to his 

 clothing when milking cows or handling milk? What precautions should he take regarding his 

 hands? With regard to the cleanliness of the cow's body, udder, and teats? What is the objection 

 to feeding hay to cows in the milking barn just before milking time ? What are the objections to 

 sweeping the barn at that time? Can you state the grades of market milk and what are the 

 qualities required in each? What is the relative market price of each? Describe the conditions 

 under which grade A milk may be produced. 



References. Waters, H. J. Essentials of Agriculture, p. 374. Ginn and Company. Harper, M. W. 

 Animal Husbandry for Schools, pp. 157-159. The'Macmillan Company. Eckles and Warren. Dairy Farm- 

 ing, pp. 177-183. The Macmillan Company. 



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