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UNIVERSITY OF ILLINOIS 
 
 Agricultural Experiment Station, 
 
 URBANA, JULY, 1902. 
 
 BULLETIN NO. 75. 
 
 STANDARDIZATION OF MILK AND CREAM. 
 
 BY OSCAR ERF, B. Sc., INSTRUCTOR IN DAIRY MANUFACTURES, 
 COLLEGE OF AGRICULTURE. 
 
 To standardize milk is to bring 1 the butter-fat content to a given 
 per cent, regardless of the quality of the milk produced by the cow. 
 
 If the milk as drawn from the cow contains less butter-fat than 
 is desired, manifestly, it can be brought to the desired standard by 
 adding 1 cream or extracting- some skim milk. 
 
 If, on the contrary, milk as yielded by the cow contains more 
 butter-fat than is necessary it can be reduced to the desired stand- 
 ard by extracting- cream or adding- skim milk. 
 
 Both of these processes are not only legitimate, but necessary ; 
 the first in the interest of the consumer and the second in the in- 
 terest of the producer, because the latter cannot afford, for exam- 
 ple, to produce milk containing- five per cent, butter-fat and sell it 
 at the price for which four per cent, milk is sold, any more than 
 the consumer can afford to pay for milk containing- five per cent. 
 
 butter-fat and receive milk which contains only four per cent 
 
 297 
 
2g8 BULLETIN NO. 75 [Jufy, 
 
 butter-fat, (providing- they are produced under equal sanitary con- 
 ditions.) 
 
 This increase or reduction of fat can be secured in another way, 
 namely, by the addition of water ; but this is not permissible, for 
 it also reduces the percentage of the solids not fat ; that is casein, 
 milk sugar, and ash ; whereas standardizing with cream or skim 
 milk does not materially alter the proportion of solids other than 
 butter-fat. 
 
 The same general methods that will serve to change the butter- 
 fat in milk to any desired quantity will also serve to produce 
 cream of any desired per cent, of butter-fat. , The necessity for 
 such standardization is set forth in Circular 51, published in April, 
 1902. It is the purpose of this Bulletin to discuss at length the 
 practical methods of standardizing. 
 
 METHODS. 
 
 In standardization, the butter-fat in milk or cream is increased 
 or decreased to an arbitrary per cent, or standard which may be 
 fixed by law or by an agreement between parties in which one 
 guarantees to furnish the other a definite quantity of butter-fat in 
 every pound of milk or cream sold for a stated price. This price 
 should vary with the butter-fat in the milk, the more butter-fat 
 for the same quantity of milk the higher the price and vice versa. 
 This is not only because the richer milk is more palatable and 
 nutritious but also because the cost of production is greater. 
 
 As was stated before, if milk contains a higher per cent, of 
 butter-fat than is desired this fat can be reduced either by separat- 
 ing the cream out of a portion of the milk or by adding skim milk. 
 In case all the milk is clarified*, the same result may be obtained 
 by mixing a less portion of the cream with the skim milk than was 
 contained in the original milk. Again, there may be an instance 
 in which no skim milk is on hand, but instead an ample supply of 
 milk with a lower per cent, of butter-fat than is desired. This 
 milk will answer the same purpose as the skim milk, but a larger 
 portion is required to bring the per cent, down to the proper 
 standard. 
 
 Again, on the other hand, milk of a lower per cent, of fat than 
 is desired may be standardized by taking out a portion of the skim 
 milk by means of a separator, or by adding reserved cream ; or, as 
 
 *Bythe term "clarified" is meant milk that has been separated for the purpose 
 of taking out some of the impurities. These impurities remain in the separator 
 bowl and the cream and skim milk are mixed again after passing through the 
 separator. 
 
39 O2 -J STANDARDIZATION OF MILK AND CREAM. 399 
 
 in the above case, if the cream is clarified, by mixing a greater por- 
 tion of cream with skim milk than there was in the original milk. 
 Here, as in the above instance, if circumstances should arise in 
 which there is no cream on hand, but instead milk of a hig-her per 
 cent, of butter-fat than the desired standard this will answer the 
 same purpose for increasing- the percentag-e of fat to the proper 
 standard. 
 
 These changes are readily effected by applying 1 a few simple 
 rules in order to calculate the quantity of skim milk to be added or 
 extracted from the whole milk so as to bring- the per cent, of butter- 
 fat to the desired point, or to mix milk of different per cents, of 
 butter-fat in such proportions as to reach readily the desired per 
 cent. 
 
 RULE I. 
 
 The amount of skim milk to be added or removed from the 
 whole milk to obtain the desired per cent, of butter-fat may be de- 
 termined by the following- rules: 
 
 Multiply the number of pounds of milk by the per cent, of fat 
 in the milk and the product will be the number of pounds of but- 
 ter-fat in the milk. 
 
 Divide the number of pounds of butter-fat in the milk by the 
 decimal representing- the desired per cent, of fat, and the quotient 
 will be the number of pounds of standardized milk. 
 
 Part i . Where the Percentage of Fat is too High. 
 
 From the number of pounds of standardized milk take the 
 number of pounds of original milk and the result will be the num- 
 ber of pounds of skim milk to be added to the original milk. 
 
 To illustrate: 1,000 pounds of milk containing 4.5 per cent, of butter-fat are 
 to be standardized to 4 percent.; how many pounds of milk must be added? 
 Since 4.5 per cent, equals the decimal .045 then, 
 iooox.045 45, the number of pounds of fat in 1000 pounds of 4.5 per cent 
 
 milk. 
 
 45-;- .04=1 125, the number of pounds of 4 per cent, or standardized milk. 
 1125 1000=125, tne amount of skim milk to be added. 
 To formulate this problem: 
 A : looo : : 4.5 : 4 
 A=the pounds of standardized milk. 
 
 1000X4.5 
 B= looo 
 
 4 
 B=the number of pounds of skim milk to be added. 
 
 Part 2. Where the Percentage of Fat is too Low. 
 With milk that is to be standardized from a lower to a hig-her 
 per cent, the same rule holds true; but in this case take the num- 
 
300 BULLETIN NO. 75. [Jnfy r 
 
 ber of pounds of standardized milk from the number of pounds of 
 original milk and the result will be the number of pounds of skim 
 milk to be removed from the original milk. 
 
 To illustrate: 1600 pounds of milk containing 3.2 percent. of butter-fat are to 
 be standardized to 4 per cent.; how much skim milk must be taken from the 
 whole milk ? 
 
 i6ooX.O32=5i .2 the number of pounds of butter-fat in the origin;! milk. 
 
 5 1. 2 -5-. 04= 1 280, the number of pounds of standardized milk. 
 
 16001280=320, the number of pounds of skim milk to be separated from the 
 
 original milk, or 
 1600x3.2 
 
 4 
 
 A=the number of pounds of standardized milk. 
 B=i6oo 1280=320. 
 B=the number of pounds of skim milk to be removed. 
 
 RULE II. 
 
 The same results may be reached by the following- rule which 
 is often more convenient than the one above given. 
 
 Divide the per cent, of butter-fat that is in the original milk 
 by the per cent, that is desired in the standardized milk. The 
 quotient multiplied by the given number of pounds of milk will be 
 the amount of standardized milk. If the quantity of standardized 
 milk is greater than the original amount of milk the difference 
 must be added in the form of skim milk; if less then that difference 
 must be separated out as skim milk. 
 
 Parti. Where the Percentage of Fat is too High. 
 
 To illustrate : 200 pounds of milk containing 6 per cent, of fat are to be 
 standardized to 4 per cent.; how many pounds of skim, milk must be added? 
 
 .06-^.04=1.5. hence 200 pounds of 6 per cent, milk must be increased by o'ne- 
 half with skim milk, or to 300 pounds. The difference between 200 pounds and 
 300 pounds is the amount of skim milk that must be added, or 
 
 A= - X 200, in which A=the final amount of standardized milk. 
 .04 
 
 Part 2. Where the Percentage of Fat is too Low. 
 To illustrate : 652 pounds of milk containing 3.1 per cent, of butter-fat are 
 to be standardized to 4.5 per cent.; how many pounds of skim milk must be ex- 
 tracted? 
 
 3. i -T-4.5=.6oi, or the fractional part of 652 pounds of 3.1 per cent, milk to 
 which the amount must be reduced in order to have the milk contain 4.5 percent. 
 butter-fat. 
 
 652X.6oi=45o. the number of pounds of 4.5 per cent. milk. 
 652450=202, tne number of pounds of skim milk to be removed, or 
 
 A== - 3 X652, in which A=the final amount of standardized milk. 
 4-5 
 
1QO2.] STANDARDIZATION OF MILK AND CREAM. 30! 
 
 RULE III. 
 
 Occasionally there may be a quick demand for milk of a per 
 cent, of fat which is not commonly produced, as is often the case 
 with city dairy companies. However, milk of a known standard 
 is always on hand. In this case a definite quantity of milk is 
 wanted and the exact proportions of milk or cream to be added to 
 the skim milk may be calculated in percentage or amount as follows: 
 
 Divide the per cent, of fat in the milk that is desired by the 
 per cent, of fat in the milk that is on hand. The result will be the 
 per cent, of the milk on hand to be taken; the remaining 1 per cent, 
 of milk will be the skim milk to be used. 
 
 To illustrate: 120 pounds of milk containing 4 per cent, of butter-fat is de- 
 sired and milk of 6 per cent, fat and skim milk are on hand to be used. What 
 per cent, of the standardized milk must be milk with 6 per cent, fat and what por- 
 tion must be skim milk; that is, how much of each must be taken in order that 
 the mixture may be 4 per cent, milk? 
 
 .04-^.06=. 66% or 66% per cent, which is the portion of 6 per cent, milk that 
 the 120 pounds of standardized milk should contain. The remaining 33^3 per 
 cent, must be skim milk which it is necessary to add to bring the fat down to 4 
 per cent. 
 
 66% per cent, of 120 pounds=8o pounds, the amount of 6 percent, milk which 
 must be mixed with 40 pounds of skim milk to bring the mixture to 120 pounds 
 of 4 per cent. milk. 
 
 RULE IV. 
 
 Part i. The actual number of pounds instead of the per cent, 
 of the different kinds of milk to be added may be ascertained as fol- 
 lows : 
 
 Multiply the number of pounds of standardized milk desired, 
 by the per cent, of butter-fat that the milk is to contain. This 
 gives the number of pounds of butter-fat in the mixture. Divide 
 this amount by the per cent, of butter-fat contained in the milk on 
 hand and the result will be the number of pounds of that milk 
 which the standardized milk should contain. The remainder 
 would be skim milk. 
 
 To illustrate: 50 pounds of milk containing 3 per cent, fat is wanted, and 
 milk containing 5 per cent, fat is to be used. 
 
 50X.03 ----=1.5, the number of pounds of butter-fat in the 3 per cent. milk. 
 1.5-^.05=30, the number of pounds of 5 per cent, milk which the standardized 
 milk should contain. 
 5030^=20, the number of pounds of skim milk to be added. 
 
 Part 2. In case there is no -whole milk on hand but instead skim 
 milk and cream of a known per cent, of butter- fat, then the cream 
 may be substituted and the fat reduced to the desired per cent, with 
 
302 
 
 BULLETIN NO. 75- 
 
 [July, 
 
 skim milk. The proportionate amounts may be calculated as in the 
 tzvo foregoing methods. 
 
 To illustrate: To make 50 pounds of milk containing 3 per cent, of fat or 1.5, 
 pounds of butter-fat as in the above illustration. If 25 per cent, cream is to be 
 substituted for 5 per cent, milk then the standardized milk would have to contain 
 6 pounds of 25 per cent, cream and 44 pounds of skim milk. 
 
 As a matter of convenience the results of the above rules cal- 
 culated on the per cent, or 100 pound basis can be tabulated in 
 such a manner as to reduce the calculation to a minimum. 
 
 TABLE 1 INDICATES QUANTITY OF SKIM MILK TO, BE ADDED TO OR 
 
 SUBTRACTED FROM 100 POUNDS OF MILK TO MAKE THE 
 
 DESIRED PER CENT. 
 
 *A 
 
 3-25 
 
 3-50 
 
 3-75 
 
 4.0 
 
 4.25 
 
 4.50 
 
 4-75 
 
 5.0 
 
 3- 
 
 - 7-693 
 
 -14.285 
 
 20.000 
 
 25.000 
 
 -29.412 
 
 -33-333 
 
 -36.842 
 
 40.000 
 
 
 - 4.616 
 
 11.428 
 
 -17-333 
 
 22.50 
 
 -27.059 
 
 -31.111 
 
 -34-737 
 
 38.000 
 
 3-2 
 
 - 1-539 
 
 - 8.571 
 
 -14.666 
 
 20.000 
 
 24.706 
 
 -28.888 
 
 -32.632 
 
 36.000 
 
 3-3 
 
 + 1-539 
 
 - 5.7I4 
 
 I2.OOO 
 
 -17.50 
 
 -22.353 
 
 -26.666 
 
 -30 527 
 
 -34.000 
 
 3-4 
 
 f 4.6r6 
 
 - 2.857 
 
 - 9-333 
 
 15.00 
 
 20.000 
 
 -24-444 
 
 28.422 
 
 32.000 
 
 3-5 
 
 f- 7-693 
 
 O.OOO 
 
 - 6.666 
 
 12.50 
 
 -17.647 
 
 22.222 
 
 -26.317 
 
 30.000 
 
 3-6 
 
 + 10.760 
 
 + 2.857 
 
 - 4.000 
 
 IO.OO 
 
 -15.294 
 
 2O.OOO 
 
 24.212 
 
 28.000 
 
 ' 3-7 
 
 +13-837 
 
 h 5-714 
 
 - i,333 
 
 - 7-50 
 
 -12.941 
 
 -17.777 
 
 -22.107 
 
 26.000 
 
 3-8 
 
 + 16.914 
 
 1- 8.571 
 
 + 1-333 
 
 5.00 
 
 -10588 
 
 -15-555 
 
 20.000 
 
 24.000 
 
 3-9 
 
 + 19.091 
 
 + 11.428 
 
 + 4.000 
 
 2.50 
 
 - 8.235 
 
 -13-333 
 
 - 17-897 
 
 22.000 
 
 4-0 
 
 +23.068 
 
 + 14-285 
 
 + 6.666 
 
 o.oo 
 
 - 5.882 
 
 II. Ill 
 
 -I5-792 
 
 20.0OO 
 
 4-1 
 
 +26.145 
 
 +17.142 
 
 + 9-333 
 
 + 2.50 
 
 - 2.429 
 
 - 8.888 
 
 -13-687 
 
 iS.OOO 
 
 4-2 
 
 +29.222 
 
 +19.999 
 
 + 12.000 
 
 + 5-o 
 
 0.076 
 
 - 6.666 
 
 -11.582 
 
 I6.OOO 
 
 4-3 
 
 +32.299 
 
 +22856 
 
 + 14.666 
 
 + 7-50 
 
 + 0.076 
 
 - 4-444 
 
 - 9-477 
 
 14.000 
 
 4-4 
 
 +35-376 
 
 +25-713 
 
 + 17-333 
 
 + 1 O.OO 
 
 f 2.429 
 
 2.222 
 
 - 7-372 
 
 I2.00O 
 
 4-5 
 
 +38-453 
 
 +28.57 
 
 +2O.OOO 
 
 +12.50 
 
 + 5.882 
 
 O.OOO 
 
 - 5-267 
 
 I O.OOO 
 
 4.6 
 
 +41.530 
 
 +31-427 
 
 +22.666 
 
 +15.00 
 
 + 8.235 
 
 + 2.222 
 
 - 3-162 
 
 8.OOO 
 
 4-7 
 
 +44.607 
 
 +34-284 
 
 +25-333 
 
 +17.50 
 
 + 10.588 
 
 + 4-444 
 
 - 1.057 
 
 6.000 
 
 4.8 
 
 + 47.684 
 
 +37-I4I 
 
 +28.000 
 
 +20.00 
 
 + 12.941 
 
 + 6.666 
 
 + 1-057 
 
 - 4.000 
 
 4-9 
 
 +50.761 
 
 +39.998 
 
 +30.666 
 
 +22.50 
 
 + 17.647 
 
 + 8.888 + 3.162 
 
 2.OOO 
 
 . 5-0 
 
 53.838 
 
 42.855 
 
 33-333 
 
 25.000 
 
 20.000 
 
 ii. in ' + 5.267 
 
 0.000 
 
 To find the pounds of skim milk to be added or removed trace 
 the vertical column of the per cent, of fat you desire down to where 
 the horizontal column representing- the per cent, of fat in the milk 
 on hand intersects and the result will be the number of pounds of 
 skim milk to be added or removed, as indicated by a plus or minus 
 sign before the result. 
 
 To illustrate: If milk containing 4.5 per cent, is desired and milk containing 
 3.8 per cent, fat is on hand, then 15.5 pounds for every hundred pounds or 15.5 
 per cent, of the quantity must be separated out as skim milk. 
 
 *Top line A represents the per cent, of fat that is desired in milk. 
 tLeft hand column B represents the per cent, of fat in milk on hand. 
 
l()O2.] STANDARDIZATION OF MILK AND CREAM. 303 
 
 To STANDARDIZE WITH WHOLE MILK OR CREAM INSTEAD OF SKIM 
 
 MILK. 
 
 RULE V. 
 
 Part i. An instance may occur in which milk is to be raised to 
 a higher per cent, -with milk of a still higher per cent, of butter- fat. 
 The quantity to be added may be found in the following manner. 
 
 From the desired per cent, of fat in the standardized milk sub- 
 tract the per cent, of fat in the milk that is on hand which con- 
 tains the lower per cent, of fat. Subtract the per cent, of fat that 
 is desired in milk from the per cent, of fat in the milk that is on 
 hand which contains a hig-her per cent, of butter-fat. Divide the 
 difference between the lower per cent, and the per cent, desired by 
 the difference between the hig-her per cent, and the per cent, de- 
 sired. The quotient will be that part of any given quantity of 
 milk containing- the hig-her per cent, that should be taken. Mul- 
 tiply the quotient by the quantity of milk of the lower per cent, 
 this will equal the quantity of milk of the hig-her per cent, to be 
 added to the milk of the lower per cent, and the sum will equal 
 the amount of the mixture containing- the desired per cent. 
 
 To illustrate: Standardize 200 pounds of milk containing 3 per cent, butter- 
 fat to 4 per cent, fat with 5.2 per cent, milk; how many pounds of the latter must 
 be added to bring the fat up to 4 per cent.? 
 
 .04 x>3=.oi. 
 
 .052 .O4 = .OI2. 
 
 .o i -4- .01 2 =.833. 
 
 200 X. 833= 1 66.6, the number of pounds of 5.2 per cent, milk to be added. 
 
 200+166.6=366.6, the number of pounds of 4 per cent, milk to be used. 
 
 Part 2. To standardize milk of a higher per cent, than is de- 
 sired with milk of a lower per cent, of fat, the same rule applies 
 except that the difference between the desired per cent, and the higher 
 per cent, must be divided by the difference between the desired per 
 cent, and the lower per cent, of butter- fat. 
 
 To illustrate: 54 pounds of milk containing 5.3 per cent, of butter-fat are to 
 be standardized to 4 per cent, with milk containing 3.1 per cent, butter-fat; how 
 many pounds of the 3.1 per cent, milk will be required? 
 
 .053 .04=. 01 3 
 
 .04 .03 1 = .009 
 
 .01 3 -=-.009 =1.44 
 
 54X1.44 = 77.76, the number of pounds of milk containing 3.1 per cent, of fat 
 to be added to the 54 pounds to decrease the fat content to 4 per cent. 
 
BULLETIN NO. 75. 
 
 [July, 
 
 RULE VI. 
 
 \ 
 
 To Find the Ratio of the Number of Pounds of Milk of the Different 
 
 Per Cents. 
 
 Subtract the per cent, of fat in the milk of the lower fat con- 
 tent from the per cent, of fat desired in the standardized milk and 
 divide this result by the difference between the fat per cents, in 
 the milk of the higher fat content and the lower fat content, the 
 quotient represents the per cent, of milk of the higher fat content 
 to be used in standardizing. 
 
 To illustrate: Find the ratio of the pounds of milk for mixing 5 with 3.5 to 
 give 4 per cent. milk. 
 
 4 3-5=-5 
 
 5-3-5 = 1-5 
 
 .5-^-1. 5=.33K r 33/4 P er cent, which is that part of the standardized milk 
 containing 5 per cent, which is used in mixing with milk of 3.5 per cent, fat con- 
 tent. Supposing 400 pounds of milk of 4 per cent butter-fat is desired then 33*4 
 per cent, of the 400 pounds or 133.3 pounds are to be milk containing 5 per cent, 
 butter-fat and 400 133.3 266.6, the number of pounds of milk of 3.5 per cent, 
 butter-fat that are to be taken to bring the fat content to 4 per cent. 
 
 Where whole milk is used for standardizing the results can be 
 tabulated equally as well as when skim milk is used. In this case 
 the whole milk has a constant per cent, in each table. 
 
 TABLE 2. To STANDARDIZE CREAM WITH MILK CONTAINING '4 
 PER CENT. OF BUTTER-FAT. 
 
 *A 
 
 17 
 
 20 
 
 22 
 
 25 
 
 27 
 
 30 
 
 tB 
 
 18 
 
 92.857 
 
 
 
 
 
 
 19 
 
 86.666 
 
 
 
 
 
 
 20 
 
 81 .250 
 
 ICO. 
 
 
 
 
 
 21 
 
 76.4706 
 
 94.706 
 
 
 
 
 
 22 
 
 72.2222 
 
 88.8888 
 
 IOO. 
 
 
 
 
 
 23 
 
 68.4222 
 
 84.2222 
 
 94.212=; 
 
 
 
 
 24 
 
 65 .0000 
 
 80.0000 
 
 90.0000 
 
 
 
 
 25 
 
 61 .QOI; 
 
 76 loot; 
 
 8; 7143 
 
 IOO. 
 
 
 
 76 
 
 59.0909 
 
 72.7272 
 
 81.8181 
 
 95.4545 
 
 . ... 
 
 
 27 
 
 56.5217 
 
 69. s6u 
 
 78.2608 
 
 91 .3044 
 
 IOO. 
 
 
 28 
 
 54.1666 
 
 66.6666 
 
 75.0000 
 
 87.5000 
 
 95.8333 
 
 
 29 
 
 52.0000 
 
 64 . oooo 
 
 72.0000 
 
 84.0000 
 
 92.0000 
 
 
 3 
 
 50 . oooo 
 
 61.5385 
 
 69 . 2308 
 
 80.3461 
 
 88.4615 
 
 lOO.OO 
 
 *A represents the per cent, of fat that is desired in cream. 
 
 fLeft hand column B represents the per cent, of fat in cream on hand. 
 
 If cream is to be standardized with whole milk the result 
 found by the intersecting columns represents the pounds per hun- 
 dred or the per cent, of the quantity which is cream of the per cent, 
 of fat on hand. 
 
IQO2.] STANDARDIZATION OF MILK AND CREAM. 305 
 
 To illustrate: If cream containing 20 per cent, of butter-fat is desired and 
 cream containing 26 per cent, of butter-fat is on hand then 72.7 per cent, of the 
 quantity desired must be cream containing 26 per cent, of butter-fat and 27.3 per 
 cent, of the quantity must be 4 per cent. milk. 
 
 STANDARDIZATION OF CREAM. 
 
 As stated above, the principal difference between milk and 
 cream is that in cream a larger portion of the water is displaced 
 with butter-fat and since the variations lie mainly between the 
 butter-fat and the water the same methods that apply to the stan- 
 dardization of milk will apply to the standardization of cream. 
 
 APPARATUS. 
 
 The apparatus that is required for standardizing- milk or 
 cream is a creamer, or much better a cream separator, a Babcock 
 tester, scales, and a mixing vat. 
 
 It requires considerable time to raise cream with a creamer 
 and on account of this, cream that is produced by this method in- 
 variably has an increased number of bacteria which when mixed 
 with fresh milk is apt to lessen the keeping quality of the stan- 
 dardized milk. It is, therefore, far more desirable and also more 
 practical to use the cream separator and since this machine is used 
 by many of the large distributing concerns for clarifying milk, it 
 at the same time answers for standardizing. Another advantage 
 is that a portion of the milk can be readily separated and the 
 cream and skim milk mixed again in the proper proportions with- 
 out delaying the delivery of the milk. Since mixing old cream 
 with the fresh milk has a tendency to increase the fermentation, 
 the cream separator should certainly supersede the old creamer for 
 standardization. 
 
 Nearly every cream separator has some contrivance by which 
 the richness of the cream can be regulated but these regulations 
 are far from accurate. A fairly uniform cream delivered by the 
 separator in daily operation may have a range of variations of five 
 per cent, above or below the per cent, desired. These variations 
 even in a minimum case would result in great profit or loss, as the 
 case may be, too great for a healthy legitimate business. To il- 
 lustrate: Take 50 gallons of cream containing 20 per cent, of 
 butter-fat and as a variation, let there be 5 per cent, more butter- 
 fat than the standard requires. Assume that the cream is sold at 
 an average price of 80 cents a gallon. The loss to the party sell- 
 ing the cream would amount to $10.00, on the 50 gallons, which 
 
306 BULLETIN NO. 7$. [July, 
 
 could have been saved by standardization. Even though each sep- 
 arator has a regulating- contrivance there are always some condi- 
 tions in practical operations which influence separation and cause 
 variation in the richness of the cream. These conditions can be 
 controlled, to a certain extent, but in order to secure as little vari- 
 ation as by standardizing- the operation will require such vigilance 
 and close supervision that it would become impracticable for the 
 creamery man as well as for the dairyman . 
 
 The first and probably the most important cause of these var- 
 iations is due to the speed of the bowl in the cream separator for 
 anything- that tends to chang-e the speed must necessarily influence 
 the per cent, of fat in the cream. Second, the temperature of the 
 milk has considerable influence on the per cent, of fat in the cream. 
 A difference of ten or more degrees in the temperature of the milk 
 will cause a decided variation in the per cent, of butter-fat in the 
 cream. If milk is warm the cream will be thicker, if cold it will be 
 thinner, other conditions being- equal. Third, the per cent, of fat 
 chang-es with the amount separated per hour. If milk is fed into 
 a separator at an uneven rate or if the flow of milk is stopped, the 
 thickness of the cream will be greatly influenced. Althoug-h 
 cream separators are nearly all provided with floats to reg-ulate the 
 inflow of the milk into the machine, yet a slig-ht variation of press- 
 ure as that due to the difference in the heig-ht of milk in the re- 
 ceiving- can or tempering- vat influences the per cent, of fat in the 
 cream. Fourth, the amount of water or skim milk used to flush 
 out the bowl at the end of separation will naturally tend to affect 
 the cream test. Fifth, the condition of the milk changes the per 
 cent, by having- small clots obstruct the cream or skim milk pass- 
 ag-e in the bowl of the separator. Of course, it is assumed that 
 milk or cream to be standardized for direct consumption oug-ht to be 
 in better condition, yet it is not uncommon to find fresh milk in which 
 a part of the casein is in such flocculent masses that when subject 
 to the pressure in the separator bowl they are readily deposited 
 on or near the opening- of the skim milk tube which slig-htly ob- 
 structs the opening- and tends to force more skim milk out with the 
 cream, hence it lowers the per cent, of fat in the cream. On the 
 other hand a mass of partially churned cream which will lodge 
 near and slig-htly obstruct the cream opening- will produce an oppo- 
 site effect by forcing- more skim milk out of the skim milk opening-, 
 thus increasing- the per cent, of fat in the cream. From this it will 
 be seen that it is practically impossible to separate cream to such a 
 constant per cent, that it is sufficiently accurate to avoid testing- 
 and standardizing-. 
 
1902.] STANDARDIZATION OF MILK AND CREAM. 307 
 
 Since it is absolutely necessary to know the butter-fat content 
 of the milk to be standardized it is essential to have a Babcock 
 tester which at any rate should comprise a part of the apparatus 
 in every dairy. 
 
 The scales and can or vat should be so arranged that the milk 
 or cream can be easily weighed and if a vat is used it should be 
 provided with a cooling- coil. It is essential that milk be cooled as 
 soon as it is milked or separated. Cream should also be cooled 
 after separating-. The cost of this apparatus for standardizing- de- 
 pends on the amount of milk handled daily. For a small dairy the 
 cost need not exceed 16.00. 
 
 SUGGESTIONS. 
 
 While it is true that a slig-ht variation in the per cent, of but- 
 ter-fat in milk or cream handled on a large scale will more than 
 pay for the extra labor in testing- the milk daily, yet on the other 
 hand it does not justify the outlay of money for labor in testing- 
 milk on a small scale. This difficulty, however, can be overcome 
 in a manner which is sufficiently accurate for the average milk pro- 
 ducer, provided all milk is to be of one standard per cnt. of but- 
 ter-fat. 
 
 As is stated in Circular 51, the quality of milk from individual 
 cows varies from day to day, still it is a fact that the mixed milk of 
 a herd of cows milked reg-ularly and kept under uniform conditions 
 will remain practically constant in butter-fat content during- a pe- 
 riod of at least three days and unless a change of cows takes place 
 in a herd or the ration is abruptly changed it will not be necessary 
 to test the mixed milk for butter-fat more than once in three days, 
 
 Immediately after milking the weight of the milk is taken and 
 it is then poured into a vat to be cooled, when all milk is in the 
 vat it is sampled and tested for butter-fat content. The proper 
 standard can then be reached by applying the foregoing methods 
 and rules. 
 
 It is quite necessary for large dairy companies to test their 
 milk daily as slight variations in large quanities will warrant good 
 returns for the extra effort in securing a more uniform product. 
 
 In creameries it ought to be an object to bring milk and cream 
 to a desired standard in butter-fat content and on account of the 
 extreme variations in the per cent, of fat in milk brought to 
 creameries it is essential that the output should be tested daily. 
 The cream is weighed while separating and run into a cooling vat 
 where it may be standardized. 
 
308 BULLETIN NO. 75. [Jufy, 
 
 Creameries that supply cream of different standards should be 
 provided with several vats in order to have the run continuous. 
 The cream in each vat must be weighed and tested to find the 
 amount of butter-fat before it can be standardized. 
 
 HOW TO OBTAIN the COST OF CREAM ON A BUTTER-FAT BASIS. 
 
 It is essential in dealing- with cream to know the price for 
 which a gallon of cream can be bought or sold which will be 
 equivalent to the price of the butter-fat it contains or the compar- 
 ative price of cream containing different per cents, of butter-fat. 
 
 Since cream is usually sold by volume it becomes necessary to 
 know the approximate weight. Average milk weighs 8.6 pounds a 
 gallon but as cream has a wide range of variations in the per cent, 
 of butter-fat it contains, it therefore, varies in weight in proportion 
 to the change in the per cent, of fat. This is due to the fact that but- 
 ter-fat is the lightest constituent in milk, having a specific gravity 
 of .93 while the average specific gravity of milk is 1.032. Hence, 
 cream containing a low per cent, of fat and much skim milk weighs 
 heavier than cream of a high per cent, of fat which necessarily 
 contains little skim milk, for this reason the weight of cream varies 
 with the per cent, of fat which it contains. Since the difference 
 in weight is but a trifle, and to avoid many standard weights in 
 commercial work, cream that ranges from 18 to 40 per cent, is usually 
 put on one basis, weighing 8.3 pounds per gallon. Any per cent, 
 below 18 is estimated on the same basis as milk ; i. e., 8.6 pounds 
 per gallon and any per cent, above 40 is estimated at the rate of 8 
 pounds per gallon. 
 
 THE PRICE PER GALLON OF CREAM EQUIVALENT TO THE PRICE OF 
 
 B.UTTER-FAT. 
 
 Multiply the pounds of cream per gallon by the per cent, of 
 butter-fat in the cream, the product will equal the pounds of fat 
 per gallon of cream. 
 
 Divide the number representing the price per gallon of cream 
 by the number of pounds of butter-fat, the quotient will equal the 
 price per pound of butter-fat. 
 
 To illustrate: What is the price per pound of butter-fat if cream containing 
 20 per cent, fat sells for 50 cents per gallon? 
 
 As stated before a gallon of 20 per cent, cream weighs 8.3 pounds. 
 8.3X.2O=i.66, the pounds of butter-fat in one gallon which is worth 50 cents. 
 $.5O-M.66=S.3O, the price of one pound of butter-fat. 
 
 To FIND THE PRICE PER GALLON OF CREAM AT A CERTAIN PRICE 
 
 PER POUND OF BUTTER-FAT. 
 Multiply the pounds of cream per gallon by the per cent, of 
 
IQO2.] STANDARDIZATION OF MILK AND CREAM. 309 
 
 fat in the cream, the product will be the number of pounds of but- 
 ter-fat in one gallon of cream. 
 
 Multiply this product by the price per pound of butter-fat you 
 desire, the product will be the price per g-allon for cream. 
 
 To illustrate: At 32 cents per pound of fat what would be the price per gal- 
 lon of cream containing 27 per cent, butter-fat? 
 
 8. 3X. 27=2.241 pounds of fat in i gallon. 
 
 2.241X32 = 71.712, or 72 cents the price of the 27 per cent, cream. 
 
 To CALCULATE THIS ON A BUTTER BASIS ^ MUST BE ADDED TO THE 
 
 BUTTER -FAT. 
 
 To illustrate: At 32 cents per pound for butter what price per gallon would 
 cream containing 27 per cent, fat be worth? 
 8.3X. 27 = 2.241, the pounds of butter-fat, 
 1-6 of 2. 24 1 =.373. 
 2.24i-f.373=2.6i4 
 
 2.614X32=83.648, or 83.6 cents the price per gallon of 27 per cent, cream 
 with butter worth 32 cents a pound. 
 
 HOW TO FIND THE EQUIVALENT 'PRICE PER GALLON FOR CREAM 
 CONTAINING DIFFERENT PER CENTS. OF BUTTER-FAT. 
 
 This is best calculated on the basis of proportion. 
 Divide the means by the extremes. 
 
 To illustrate: If cream containing 20 per cent, butter-fat is worth 60 cents 
 per gallon what is cream worth containing 25 per cent, butter-fat? 
 .20 : .25 : : .60 : x 
 6ox. 25 = 15 
 
 15-^.20=75, or 75 cents, the equivalent worth of 25 per cent, cream in com- 
 parison to the worth of 20 per cent, cream at 60 cents a gallon. 
 
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