90 THE BOOK OF CHEESE 



sour milk, principally lactic acid. The group falls natu- 

 rally into two sections : (1) the cheeses made from milk 

 curdled by souring ; (2) those for which the milk is curdled 

 by souring and rennet. In the latter group both agencies 

 are necessary to the resulting product. The time required 

 to curdle by souring alone is longer than when rennet 

 is used; this period is usually longer than necessary for 

 the cream to rise by gravity; hence the cream is either 

 skimmed off or removed with the separator beforehand. 

 The curd, therefore, is essentially a skimmed-milk curd. 

 Casein curdled in this way tends to become granular 

 or " rough," to feel " sandy " when rubbed between the 

 fingers. Heating is commonly necessary to lower the 

 water-content of the mass even to 75 per cent. Such 

 curd tends to become hard or rubbery when heat is ap- 

 plied. In this group, the best known form is variously 

 called " cottage " cheese, " clabber " cheese, schmier- 

 kase. 



111. Cottage cheese is made from skimmed-milk, 

 soured by lactic bacteria until a curd is formed. This 

 is done preferably at about 20 C. (70 F.), because at 

 this temperature the purely lactic type of organism has 

 been found to outgrow competing forms which may be 

 present. Starter containing the desired culture, if prop- 

 erly used, saves much time in the curdling period. Such 

 curdling requires at least twelve to twenty-four hours, 

 frequently much longer unless abundant starter is intro- 

 duced. 



112. Household practice. The details of cottage 

 cheese making in the home differ widely in separate sec- 

 tions and even in different families in the same part 

 of the country. The essentials of the practice, common 

 to all, include : (1) curdling the whole milk by natural 



