THE MILK CONTRACTOR 295 



they are full, while at half capacity they are half full, which permits the 

 pasteurizing of small batches of milk. 



3. The holder consists of eight shallow pans arranged in two tiers 

 and supported in an insulated copper-lined case with enamel sides. The 

 intake from the heater discharges automatically and alternately into the 

 top pan of each tier, the milk being held positively in each pan one-fourth 

 of the total selected holding time and then being automatically passed 

 to the pan below. It is claimed that the passage of milk from one pan to 

 another makes agitators to prevent separation of the fat solids unnecessary. 



Holders of the Continuous Type. The continuous method is less 

 satisfactory than the positive; the milk is retarded in its course to the 

 cooler so that theoretically it is kept at the pasteurizing temperature long 

 enough to ensure its being thoroughly pasteurized. In reality, owing 

 to the unequal movement of different parts of the milk stream, some 

 of the milk travels toward the cooler more rapidly than the rest and so is 

 inadequately heated. The machines never work up to their rated 

 efficiency. There are three general types of retarders: 



1. This apparatus consists of an upright cylindrical tank or of two or 

 more such tanks arranged in series. The milk is fed in at the top and 

 passes out at the bottom into another tank or if a single tank is used the 

 outlet pipe is carried up nearly to the top of the tank and downward again 

 to the cooler, thus permitting no milk to discharge from the tank till the 

 milk therein reaches the level of the top of the outlet pipe. Single tanks 

 are unsatisfactory for the milk tends to stratify with the hot milk at the 

 top, consequently the milk in different parts of the tank is held unequally. 

 Holders of this type are difficult to clean and are said to have a holding 

 efficiency of but 25 to 50 per cent, of their theoretical capacity. 



2. Holders of this sort are horizontal tanks with cross-partitions or 

 baffles to impede the flow of milk through the tank from one end to the 

 other. The best show an efficiency of from 10 to 15 per cent, of their 

 theoretical capacity. 



3. Machines of this type are horizontal tubular holders in which 

 the milk enters the topmost of a series or bank of tubes and passes back- 

 ward and forward through them all, till it emerges from the bottom tube. 

 Tubular holders have an efficiency of from 80 to 85 per cent, of their 

 theoretical capacity. As in the case of the tubular heaters, it is difficult, 

 owing to the slight inclination of the tubes, to remove the last milk at the 

 end of the run. Pains must be taken to clean the tubes thoroughly. 

 Heaters of every type must be warmed with steam before running milk 

 through them, otherwise the first milk to pass is apt to be cooled below the 

 pasteurizing temperature with the result that the bacteria it contains are 

 not killed. 



Regenerative Pasteurizers. The object of regenerative pasteurizers 

 is to economize heat and ice. This is effected by utilizing the hot milk 



