260 



THE CHEMICAL CONTROL OF THE DAIRY. 



Composition of Skim Milk. — Skim milk diiiers practically 

 from whole milk in the percentage of fat. In milk from which 

 the cream has been removed by skimming very wide variations 

 are found in the percentage of fat ; it varies from 0'4 per cent, 

 to over 2 per cent. Much lower percentages are found in separ- 

 ated milk, and the limits, 0-05 per cent, to 0-3 per cent., are very 

 rarely overstepped. By the removal of the fat the percentage 

 of other solid constituents are slightly raised in amount ; this is 

 caused by the constituents which were contained in 100 parts 

 being left in about 96i parts, by the removal of 3J parts of fat. 



The following is the average composition of well-prepared 

 separated milk : — 



Control of Separators — The most important point in the 

 control of separators is the estimation of the fat left in the separ- 

 ated milk. A separator leaving a proportion of fat appreciably 

 higher than that deduced from the formula given above is working 

 badly, and the cause should be at once investigated. It is im- 

 portant that the speed be properly maintained, that the milk 

 be at the right temperature, and that the exit tubes be not 

 clogged up ; the chemist should make a practice of visiting the 

 separators daily while they are running and of checking the 

 speed and temperature of the milk. At least one sample o£ 

 separated milk should be tested from each " run " of the separ- 

 ator ; these samples should be taken from the skim outflow 

 tube, at some period of the run, preferably not immediately after 

 starting. 



A further means of controlling the separators is to compare 

 the total weight of the fat in the cream, separated milk, and 

 the milk left in the drum after separating, with the total weight 

 of the fat in the milk separated. This is done by weighing each 

 product, multiplying the weight by the percentage of fat and 

 dividing by 100. The total weight of fat in the cream and 

 separated milk should be nearly equal to that in the milk, the 

 difference representing loss in separating ; the average loss 

 should not amount to more than 2 per cent, of the total fat in 

 the milk. 



Separator Slime. — After running a separator a viscous sub- 

 stance is found on the inside of the drum. It is usually of a 

 dirty white colour ; but if the milk contains much solid impurity,. 



