444 SCIENCE AND PRACTICE OF CHEESE-MAKING 



and shaking vigorously for a few seconds after each 

 addition. It is usually safe to add about 25 cc. of acid 

 before examining the milk to see if the casein-separates 

 in the form of white flakes. After adding 20 to 25 

 cc. and shaking, the mixture is allowed to stand still. 

 If enough acid has been added, the casein separates 

 promptly in large, white flakes, and on standing a 

 short time the liquid above the settled casein appears 

 clear and not at N all milky. If the addition of 25 cc. 

 of acid is insufficient, add I cc. more of acid and shake ; 

 continue the addition of acid I cc. at a time, until the 

 casein is observed to separate promptly and completely 

 on standing at rest for a short time. The number of 

 cc. of acid used to effect precipitation is noted and this 

 result is recorded as A. 



(b) Influence of temperature. For convenience of 

 work and uniformity of results, the temperature of the 

 mixture at the time of the addition of acid may be be- 

 tween 65 and 75 F. Under these conditions, many 

 milks give satisfactory results with just 30 cc. of acid. 

 In case of milks containing 3.5 to 4 per cent of casein, 

 one may need to use as much as 35 to 40 cc. of acid. 

 Rarely has it been found that 25 cc. of acid is ex- 

 cessive. The amount of acid may be 2 or 3 cc. in ex- 

 cess of that required to effect complete precipitation 

 without seriously affecting the accuracy of the results, 

 provided the temperature of the mixture is below 

 75 F. At temperatures above 75 F., good results are 

 attainable, but care must be taken not to use much 

 excess of acid; and, of course, the higher the temper- 

 ature, the less will be the amount of acid required. In 

 working at temperatures under 65 F., the casein sepa- 

 rates more slowly or requires more acid to separate 

 promptly. When working with milk that is much 



