THE MILK CONTRACTOR 297 



the putting on the market, in 1910, of a size thereof especially adapted to 

 milk bottles made it possible to submerge the bottles for pasteurization 

 and led to the adoption of pasteurization in the final package on a com- 

 mercial scale. Since that time other caps adopted to this sort of pas- 

 teurization have appeared. One of the first to adopt the bottle process 

 was Robert Burnett who has used it under the direction of Prescott at his 

 Deerfoot Farm in Southboro, Mass., since Aug. 1, 1911. D. Whiting & 

 Sons, also of Boston, under the direction of Stedman Bixby have pas- 

 teurized a part of their supply by this method since September, 1911. 



In practical work the bottles are filled with milk to a level that leaves 

 about 2 per cent, of their total capacity as an air space. They are then 

 capped and heated in water that has a temperature of about 150F. for a 

 period of 30 min. from the time the milk reaches 145F. They are then 

 gradually cooled and are finally put in cold storage. Commercial houses 

 have long had data as to the efficiency of the method but Ayres and John- 

 son and also Hammer are the first to publish results of careful studies of 

 the process. 



The two former authors find that pasteurization in the bottle at 145F. 

 for 30 min. gives satisfactory bacterial reductions. They advise that in 

 order to destroy heat-resisting organisms, which may survive the pasteuriz- 

 ing temperature, the bottles be steamed for at least 2 min. before being 

 filled with milk. They observe that during the period the milk is being 

 heated the temperature varies markedly in different parts of the bottle. 

 If milk at 50F. is heated in bottles without agitation, in water at 146F., 

 the temperature at the top of the bottle will reach 140 C F. about 9 min. 

 before that in the bottom does. In actual pasteurization the bulb of the 

 thermometer should be placed about J^ in. from the bottom of the con- 

 trol bottle. If bottles with chipped or otherwise imperfect tops are used, 

 serious contamination of the milk may result from leakage of the water 

 into the milk. 



Hammer's results are in general accord with those of Ayres and John- 

 son, but he advises an exposure of 50 min. in water at 145F. for milk in 

 half pint, pint and quart bottles and, basing his opinion on experiments 

 with pint bottles, concludes that this exposure would be satisfactory also 

 for cream. Milk pasteurized at 145F. for 50 min. soured slowly with a 

 typical lactic acid curd and without gas formation. As the vat tempera- 

 ture was increased above 145F., the results were progressively undesirable 

 until at temperatures between 160 and 170F., the cream line was inter- 

 fered with and a cooked flavor imparted to the milk. The flavor of the 

 milk, pasteurized as recommended, was acceptable to most people. Unde- 

 sirable flavors in the raw milk were not decreased by this method of pas- 

 teurization and sometimes they were intensified. In some cases a flavor 

 was imparted to the milk by the paper lining of the cap and to remedy this 

 the manufacturers made a cap with a parchment paper lining. Instances 



