HEAT IN THE PRESERVATION OF FOOD ^PRODUCTS. 387 



organisms are destroyed, thus aiding in the prevention of such diseases 

 as might otherwise be conveyed through this product. In creameries, 

 the usual method of pasteurization is what is known as the continuous 

 process, in which the milk is subjected to a momentary heating at about 

 85, the flow through the pasteurizing apparatus 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 or invalid feeding, a lower 

 temperature is employed. A temperature sufficiently high to destroy 

 the organism of tuberculosis (the standard for pasteurization) by momen- 

 tary heating, imparts to the milk a cooked flavor, making it less palata- 

 ble; coagulates some of the protein constituents, rendering it less di- 

 gestible; and affects the enzymes present, thus "devitalizing" the milk. 

 The desired end may be reached, however, by employing a lower tempera- 

 ture for a longer period of time, and the method generally recommended 

 is to heat the milk to 60 to 65 for twenty minutes. This heating is 

 sufficient to render harmless any pathogenic organisms likely to be present 

 in milk, without the objectionable features attendant upon heating to a 

 higher degree (p. 319). 



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

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

 ever, milk 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 temperature 

 of 40 to 50, until the volume is reduced to one-third or one-quarter of 

 the original. The evaporation must be conducted with great care, 

 otherwise the lactose crystallizes out and this causes the product to feel 

 "sandy" on the tongue. Condensed milk is made either with or without 

 the addition of cane sugar. When used at all, it is added in the propor- 

 tion of about 10 to 12 per cent of the weight of the milk. When the 

 evaporation of the milk is finished, the yellowish white syrup is sealed 

 up in tins which hold about 450 g., and this quantity is equivalent to 

 about i 1/2 liters of normal milk. The addition of cane sugar acts as 

 a preservative, and although the finished product may contain some living 



