1917] DAIRY FARMING DAIRYING. 175 



relative rate of cooling for bottles exposed to still air and moving air vi'as the 

 same as that for pint bottles, but the time required for cooling through the above 

 range was longer. In a room temperature of 42° milk in the 10-galloa cans was 

 reduced from 147 to 90° in 6* hours in still air and in 2 hours and 15 minutes 

 in moving air. 



In cooling experiments performed on a 30-crate basis in which the air was 

 forced from the ))ottom upward, it was found that the variation in temperature 

 in different sized bottles and the same sized bottles at different positions in the 

 stack was too great for satisfactory commercial operation. Consequently in the 

 next experiments the direction of the air through the stack was reversed periodi- 

 cally, the cold air being blown through from the bottom for 15 minutes and then 

 through from the top for the same period. It was found that while the difference 

 in temperature between the top and bottom bottles was decreased to a certain 

 extent by reversing the air, still there was too great a difference for satisfactory 

 operation commercially. 



In experiments in which the air was forced from the top downward it re- 

 quired 2 hours and 10 minutes to reduce the temperature of the lower quarts to 

 50° when the temperature of the incoming air was 40° ; 1 hour and 35 minutes 

 \\hen the temperature of the incoming air was 30° ; and 1 hour and 20 minutes 

 when the temperature of the incoming air was 20°. In these experiments with 

 the incoming air temperature at 40° the average difference in temperature be- 

 tween the lower quart and upper pint at the end of the cooling period was 8.9°, 

 and with the incoming air at 30° the average difference was 2.49° and maxi- 

 mum difference 4.5°. 



When a bottle was cooled by an air blast from the bottom of the stack there 

 was a difference in temperature between the top and bottom of the bottle of 

 about 8° when the fan was started and 23° 22 minutes later. When the air was 

 forced downward through the crate of bottles this difference between the top 

 and bottom of individual bottles was practically eliminated. 



In experiments on the cost of cooling by means of cold outside air it v,-as 

 found that under the conditions of the experiments and assuming a cost of 6 

 cts. per kilowatt hour for electric energy, the cost of power per ton of refrigera- 

 tion was $1.11. Under commercial conditions it is estimated that the cost would 

 be only about G6 cts. per ton of refrigeration. These figures are based on an 

 outside air temperature of 40° or lower. 



In order to obtain data on the effect of slow cooling on the bacterial content 

 of milk after pasteurization, ten experiments made in which milk was first 

 pasteurized and bottled hot in steamed bottles. For the ten bottles cooled 

 within one-half hour in ice water the average number of bacteria per cubic 

 centimeter was, directly after pasteurization, 5,823; after 17* hours in the 

 refrigerator at 45°, 5,040; and taken from the refrigerator IS hours after 

 pasteurization and held for 6 hours at 75 to 86°, 6,908. For the ten bottles of 

 milk cooled slowly at room temperature for four hours the average number of 

 bacteria per cubic centimeter was, directly after pasteurization, 5,727 ; after 14 

 liours in the refrigerator at 45°, 4,678 ; and taken from the refrigerator 18 hours 

 after refrigeration and held for 6 hours at 75 to 86°, 5,583. The average bacterial 

 content of the ten samples of raw milk in this experiment was 264,375 per 

 cubic centimeter. On checking these results in a test with pasteurized milk 

 cooled on a small commercial scale it was found that when the bacterial con- 

 tent of raw milk was high there was a marked reduction in the number of 

 bacteria during the process of cooling by forced air circulation. However, 

 the authors state that the period of cooling to 50° should not exceed five hours. 



I 



