440 SCIENCE AND PRACTICE OF CHEESE-MAKING 



hand, until the surface has been well dried. The curd 

 is then gently pressed against the portion of the iron 

 where it is hot enough to make the curd stick to 

 the iron but not hot enough to scorch it. The curd is 

 then carefully drawn away from the iron and, if in 

 proper condition, produces fine, silky threads, the 

 length of which depends upon the amount of acidity 

 of the curd. 



VOLUMETRIC TEST FOR CASEIN 



A new test for casein has been recently worked out 

 at the New York experiment station by Van Slyke and 

 Bosworth (Technical Bulletin No. lo, Sept., 1909). In 

 outline the method is as follows : Into a 200 cc. flask 

 one measures 17.5 cc. (18 grams) of milk, adds about 

 80 cc. of water and i cc. of phenolphthalein, after which 

 a solution of sodium hydroxid (caustic soda) is added 

 until the mixture is neutral. Standardized acetic acid 

 is then added until the casein is completely precip- 

 itated, the volume of the mixture is made up to 200 cc. 

 by addition of water and then filtered. Into 100 cc. 

 of the clear filtrate, a standardized solution of sodium 

 hydroxid is run until neutral. The solutions are so 

 standardized that i cc. is equivalent to i per cent of 

 casein in the milk examined. Therefore, the number 

 of cc. of standard acid used, divided by 2, less the 

 amount of standard alkali used in the final titration 

 gives the percentage of casein in the milk. The opera- 

 tion usually requires 12 to 15 minutes when apparatus 

 and solutions are at hand in convenient form ready for 

 use ; several determinations can be carried on at the 

 same time with much relative economy of time. 



