150 SCIENCE AND PRACTICE OF CHEESE-MAKINC 



calcium lactate, a compound which is neutral 

 (neither acid nor alkaline), and which does not 

 taste sour. Under the usual forms of fermentation, 

 milk-sugar forms small amounts of other com- 

 pounds in addition to lactic acid. The sour smell 

 of whey and of sour milk is not due to free lactic 

 acid, since pure lactic acid has practically no odor, 

 but is caused by some of the other fermentation 

 products formed, the exact nature of which is not 

 fully known. 



THE SALTS OF MILK 



The salts of milk, commonly represented by the 

 term *'ash," are present in only small amounts, but 

 they have extremely important relations to the 

 process of cheese-making. Our knowledge of these 

 compounds is very incomplete. The salts of milk 

 are commonly spoken of as the ash or mineral con- 

 stituents. This conception is somewhat misleading, 

 because the materials appearing in the ash of milk 

 are, to some considerable extent, combined in or- 

 ganic compounds, instead of existing in milk as 

 separate inorganic bodies in the form in which they 

 appear in the ash. The ash, therefore, represents 

 in amount more than the so-called mineral con- 

 stituents of milk and less than the salts of milk. 

 While the average amount of ash in milk is about 

 0.7 per cent, the amount of salts is probably much 

 nearer 0.9 per cent. To illustrate this point in more 

 detail, the citric acid which is present in milk in 

 the form of citrate salts does not appear at all 

 in the ash, since it is destroyed in burning the milk 

 to obtain the ash. In cheddar cheese the ash, not 



