Condensed Milk and Milk Powder 161 



the Gebee seal with the burr cap, and the McDonald seal with the 

 friction cap, the seal is not absolutely air-tight. While the pores 

 between cap and can are microscopic in size, and not large enough 

 to permit the contents from leaking out, they are sufficient to admit 

 ain The cans are usually filled with the condensed milk at a tem- 

 perature of about 70 degrees F. If the filled and sealed cans are 

 exposed to a very low temperature, as may be the case in winter, in 

 store houses or in transit, the milk and the air in the cans contract. 

 This contraction is intensified by the fact that the sweetened con- 

 densed milk does not freeze. Its concentration is so great that its 

 freezing point is usually below the most extreme cold storage tem- 

 perature. This contraction of milk and air in the cans produces a 

 partial vacuum, causing air to be drawn into the cans through the 

 microscopic openings of the seal. When the cans are subsequently 

 moved into places with a more moderate temperature, the milk and 

 the air in the cans expand, but the milk on the inside of the cans 

 forms a seal preventing the escape of the surplus air. The result 

 is that the ends of the cans bulge. This phenomenon has been ex- 

 perimentally determined by the author. 1 While the contents of such 

 cans are perfectly normal, the package suggests fermented milk and 

 •may be rejected on the market. 



It is evident, from the above data, that the swelling of the cans, 

 as the result of exposure to excessively low temperatures, can 

 readily be avoided, either by protecting the cans against excessive 

 cold, or by using cans that are sealed with solder. The solder- 

 seals are hermetical so that no air can be drawn into the cans when 

 a partial vacuum is formed in their interior as the result of the 

 contraction of air and milk. 



Rancid Sweetened Condensed Milk 



General Description. — 'Sweetened condensed milk may de- 

 velop a distinctly rancid flavor and odor, a defect which renders 

 it unmarketable. 



Causes and Prevention.— -While the exact causes of the de- 

 velopment of rancidity in dairy products are as yet not well 

 understood, it has been demonstrated experimentally that rancidity 

 as well as other allied off-flavors, such as oiliness, tallowiness, fish- 

 iness, etc., are closely associated with the decomposition of some of 



2 Hunziker, Results not published 



