184 SCIENCE AND PRACTICE OF DAIRYING. 



hands during working, but to carry out the first and second kneading on 

 the butter-worker. 



99. Yield of Butter. Of a very large number of churns which 

 have been constructed and recommended in the course of time, 

 only a very small number have succeeded in establishing them- 

 selves in general practice. With all the useful churns, if properly 

 handled, a yield of butter can be obtained from a fluid, which 

 approximates to the percentage of fat it contains. This explains 

 how the amount of the yield of butter in proper churning is almost 

 always solely dependent on the percentage of fat in the milk, and 

 on its successful removal in the cream. From experience, and a 

 large number of experiments, it is known that it is easily possible 

 to obtain about 97 per cent of the entire fat in the form of butter 

 when sour cream containing 15 to 25 per cent of fat is employed; 

 89 per cent when sour milk is used, and 86'5 per cent when sweet 

 cream of 15 to 25 per cent of fat is employed. If the percent- 

 age of fat in milk be denoted by the letter /, and the finished butter 

 contains 84 per cent of fat, the yield of butter x, in the case of 

 churning with sour milk, may be easily obtained by the following 



formula: 



= !. 06x/ 



and in the case of churning soured cream, when the percentage of 

 fat in the skim-milk obtained is '25 per cent, by the formula: 



0; = 1- 155 x/- -2454. 



It would be very simple and easy to calculate similar formulae 

 for other cases. Such formulas are extremely important and useful 

 for occasional testing of the results of the manufacture of butter in 

 dairies. By calculating the yield of butter, for example, in the 

 case of a known percentage of fat in milk, and by comparing the 

 result obtained with that actually yielded in practice, it is shown 

 whether what is, as a rule, easily obtainable, has been really obtained 

 or exceeded, or whether, owing to existing unfavourable circum- 

 stances, it has not been obtained. 



In practice, the yield of butter is generally found by weighing the 

 butter obtained, and by dividing the number denoting the weight of the 

 milk used by the number denoting the weight of the butter. In this 

 way we learn how many parts by weight of milk have been required 

 for each part of butter by weight obtained. By dividing the number 



