HEAT 181 



jectionable to many consumers. It has often been stated 

 that heated milk is less digestible and likely to cause nu- 

 tritional troubles in children. 



Milk contains growth-stimulating substances of an un- 

 known nature. These bodies are known as vitamines. The 

 heating of milk partially destroys these important sub- 

 stances, and for that reason becomes an objectionable proc- 

 ess. The advantages of pasteurization greatly outweigh 

 the disadvantages. If it seems desirable, the loss of vita- 

 mines in milk, due to the heating thereof, can be compen- 

 sated for by the feeding of fruit juice, especially that of 

 the orange. Cases of malnutrition and abnormal develop- 

 ment of the bones, rickets, have likewise been ascribed to 

 heated or pasteurized milk. But there is no reason to be- 

 lieve that milk as now treated is more likely to be the 

 cause of such troubles than is raw milk. In fact, milk 

 heated to the boiling-point is successfully used with chil- 

 dren. 



In the treatment of any food the degree of heat necessary 

 to destroy the organisms is dependent on the length of time 

 the material is exposed to its action. Low temperatures 

 for long periods of time may be as effective as higher tem- 

 peratures for shorter exposures. In the pasteurization of 

 milk, the exposure may be at 145 F. for from twenty to 

 thirty minutes or 160 F. for dne minute. Either of these 

 methods will insure the freedom of the milk from patho- 

 genic bacteria, and will destroy such a proportion of the 

 acid-forming bacteria as to improve the keeping qualities 

 of milk. In actual practice no method has been devised 

 by which milk can be heated momentarily with perfect suc- 

 cess. In machines designed for this so-called' flash method 

 of heating, the milk is allowed to flow through the heating- 

 chamber in a continuous stream. In such a device the 

 rate of flow is not uniform in all parts of the machine. 



