25.6 Milk and Its Products 



fold and important part. The curd is contracted to 

 some extent by the action of the rennet still con- 

 tinuing ; also to some extent by the direct applica- 

 tion of the heat, but to a greater extent by the 

 effect of lactic acid upon the curd, the production 

 of lactic acid being greatly favored by the increased 

 temperature. It is desirable that this contraction of 

 the curd in the cooking stage go on uniformly through- 

 out the whole mass. The heat is therefore applied 

 gradually and with constant stirring. As the parti- 

 cles of curd shrink in size, the tendency for them 

 to unite in masses constantly diminishes; and they 

 are broken with greater difficulty, so that while at 

 first extreme care is necessary to prevent the par- 

 ticles of curd from becoming broken, as the temper- 

 ature rises, the stirring may become more rapid and 

 vigorous. The heat should be raised slowly from 

 the setting point of the milk up to 98 F., and it 

 should not be more rapid than 2 in five minutes; 

 and unless the lactic acid develops very rapidly it 

 is better to take even more time than this. When 

 the temperature of 98 F. is reached, the stirring 

 may cease and the particles of curd be allowed to 

 settle upon the bottom of the vat until the curd is 

 thoroughly shrunken and a sufficient amount of 

 lactic acid has been developed. At the end of the 

 cooking stage the particles of curd should have 

 shrunken to less than one -half of their former size, 

 and should have become so hard that when pressed 

 together between the hands, and the pressure sud- 

 denly relaxed, they will fall apart, and show no 



