HEAT IN THE PRESERVATION OF FOOD PRODUCTS 463 , 



conveyed through this product. In creameries, the usual process of 

 pasteurization is what is known as the continuous or flash process, in 

 which the milk is subjected to a momentary heating to about 8^°, 

 the flow through the pasteurizing machine being so regulated as to 

 bring all the milk up to the desired temperature, the heating being 

 immediately followed by rapid cooling, and subsequent addition of the 

 lactic starter. 



In the pasteurization of milk for infant feeding, a lower temperature 

 is employed. A temperature sufficiently high to kill the organism of 

 tuberculosis (the standard for pasteurization) by momentary heating, 

 imparts to the milk a cooked flavor, making it less palatable, and coagu- 

 lates some of the protein constituents making it less digestible. The 

 desired end may be reached however, by using a lower temperature for 

 a longer period of time, and the method generally recommended is to 

 heat the mUk to 60° to 65° for thirty minutes. This heating is suffi- 

 cient to render harmless any pathogenic organisms likely to be present 

 in the milk, without the objectionable features attendant on heating 

 to a higher degree. 



Condensed Milk. — It is commonly stated that Gail Borden invented 

 the process for preparing condensed milk, in 1856. Previous to this 

 however, mUk had been condensed in France, Germany, and England 

 as early as 1825 to 1835. While he cannot, therefore, be called the 

 inventor of condensed milk, to Borden belongs the credit of having 

 first prepared it by a rational process, and in a practicable form. 



In the manufacture of condensed milk, good fresh milk is evaporated 

 in a vacuum pan similar to those used in sugar factories, at a tempera- 

 ture of 40° to 50° until the volume is reduced a little more than half, 

 cane sugar being added so that the finished condensed milk usually 

 •contains 40 per cent, cane sugar. The evaporation must be conducted 

 with great care, otherwise the lactose crystallizes out, and this causes 

 the product to feel "sandy" to the tongue. When the evaporation 

 of the milk is complete, the yellowish white syrup is sealed up in tins 

 which hold about 450 g., and this quantity is equivalent to about i}4 1- 

 of normal milk. The addition of cane sugar acts as a preservative, 

 and although the finished product may contain some living organisms, 

 it is said to keep indefinitely if unopened, and will even keep for a 

 number of days after opening. ' Occasional losses do occur by spoilage 

 of the finished product, either from the growth of occasional types 



