346 MILK AND DAIRY PRODUCTS 



same food, for example, fed to different breeds produces 

 different kinds of milk, but changing the food for one par- 

 ticular breed does not change the kind of milk produced 

 by that breed. There are some exceptions to this statement, 

 but they are not of sufficient importance to be discussed 

 here. 



246. Adulteration and Preservation. — Since milk has be- 

 come such a very valuable food product, the temptation 

 to adulterate it is very great. The addition of water is the 

 commonest method of adulteration, detection of which is 

 not particularly easy. For example, the specific gravity of 

 milk might be used as a test for purity, but by removing 

 fat and adding water, the specific gravity can be made to 

 remain the same. It is, however, a requirement in some 

 states that milk shall not be sold under a certain content of 

 butter fat. This serves as a protection to the consumer, 

 but in some instances it works a hardship against the pro- 

 ducer for it is quite possible that perfectly pure milk may 

 contain less than the stated legal minimum amount of fat. 



Milk is not only a perfect nutrient for man, but it is also 

 a perfect nutrient for bacteria, and exposure to the air for 

 any length of time permits the entrance of large numbers 

 of bacteria, many of them dangerous to health. No bacteria 

 are present in the milk within the animal, but as soon as it 

 is drawn bacteria begin to accumulate. Since bacteria thrive 

 best in warm milk, immediate cooling is of help in preventing 

 their activity to some extent. 



There are two ways of freeing milk from bacteria, which 

 are legitimate. One is by pasteurization which consists 

 in heating the milk to a temperature of 60° to 80° C. for 

 twenty minutes, and then cooling it. This treatment kills 

 practically all of the bacteria, and if carried out in sealed 

 containers no more bacteria can enter. Pasteurization does 

 not alter the taste or smell of the milk, and is practised 

 quite largely by the best dairies. 



The other way of treating milk is by sterilization which 

 consists in heating the milk to 115° C., accomplished by 

 steam under pressure. This absolutely kills all bacteria, 

 but it alters the taste and smell of the milk. Albumin is 



