6 



BULLETIN 1123, U. S. DEPARTMENT OF AGRICULTURE. 



Cream. — The 150 pounds of 28 per cent cream does not contain more 

 fat than is needed; hence the entire amount can be used. 



The amount of 34 per cent cream can be determined by subtracting 

 the amount of fat added by the 1 50 pounds of 28 per cent cream from 

 the total amount required and dividing the remainder by 0.34, thus: 



157.5- 42 -115.5. 



115.5-1-0.34 = 340 pounds of 34 per cent cream, 



STcim milk and condensed skim milk. — From these two ingredients 

 must come the balance of the constituents (milk solids not fat) of the 

 mix. To find the proportions subtract the sum of the milk solids not 

 fat in the cream from the total amount required and divide by 927.5, 

 the difference between the amount of ingredients already used and 

 the total (1,750) pounds required. For instance: 



210- (10-f20.8) = 179.2. 



(179.2 H- 927.5) X 100 = 19.3 per cent solids. 



This gives the per cent of solids not fat that the additional 927.5 

 pounds of mix must contain. To find the proportion of skim milk and 

 condensed skim milk necessary, the "square method" is used. The 

 calculations for the square method * are as follows : 



Skim milk 9 



Condensed milk 27 



7.7 



10.3 

 18.0 



927.5-f-18=51.53 number of unit portions in total mix. 

 51.53X7.7=396.78 pounds of skim milk in total mix. 

 51.53x10.3=530.75 pounds of condensed skim milk in total mix. 



The accuracy of the calculation can be ascertained by comparing 

 the sum of the figures in each column with the stipulated amounts 

 placed at the top of each colmnn. 



When this is done, the ingredients are proportioned by careful 

 weighing. The mix is then ready to be pasteurized and homogenized. 



1 The square method, sometimes called the Pearson method, may be used to find the proportion of milk 

 and cream necessary in standardizing either the fat or the milk soUds not fat in milk and cream. Tlie 

 purpose of the s(iuare is to separate the three principal factors in making the calculations, and to keep the 

 deductions straight after the calculations have been made. For instance, in this particular problem, 

 which is to find the proportion of sMm milk and condensed skim milk necessary in making 927.5 pounds of 

 skim milk containing 19.3 per cent milk soUds not fat, the three principal factors are: First, the rnilk sohds 

 not fat content desired in the mixture; second, the milk soUds not fat content of the skim milk; and third, 

 the milk soUds not fat content of the condensed skim milk. The first factor (19.3 per cent) is placed in the 

 center of the square; and the other two factors (9 per cent and 27 per cent) are assigned to the corners on the 

 left-hand side of the square. When this has been done, two calculations are made and placed as follows: 

 (1) The diflerence between the upper left-hand figure (9) and the center figure (19.3), which is 10.3, is placed 

 in the lower right-hand comer of the square, and indicates the number of pounds in a unit portion of the 

 condensed skim milk required in the proposed mixture. Similarly the difference between the lower left- 

 hand figure (27) and the center figure (19.3) which is 7.7, is placed, in the upper right-hand corner of the 

 square, and indicates the number of pounds in a imit portion of the skim milk required in the projiosed 

 mixture. Having ascertained the weight of one unit portion of each of these ingredients, any quantity 

 of the desired mixture can easily be made by adding these two together to find the weight of one uiiit portion 

 of the mixture desired, and then multiplying this by the number of unit portions in the total mix, as shown 

 in the above example. The same procedure is used in standardizing the fat contents of milk and cream. 



