Live Stock. 



42 



[July, 1908. 



were cooled by either ice or travelling 

 refrigerating machines, there is no doubt 

 that a considerable addition would be 

 made to the cost of carrying. It is, 

 therefore, evident that in a great 

 number of cases when milk arrives at a 

 town's dairy it arrives in a condition 

 when it is charged with bacteria, which 

 have been taken up from the air, dust, 

 or general surroundings, during the 

 journey. We have already emphasised 

 the fact that it does not necessarily 

 follow that these bacteria are injurious. 

 On the other hand, it is quite possible 

 that they may be harmful, as the 

 methods of ascertaining the presence of 

 disease in cows are not of a very perfect 

 character, and, as general inspection of 

 country byres is not complete, then we 

 are bound to assume that the milk as it 

 arrives in a town is contaminated. The 

 mere fact that there is a possibility of 

 tuberculosis of the udder existing is in 

 itself a hidden danger which must be 

 dealt with. The number of cows sub- 

 ject to tuberculosis of the udder has 

 been variously stated, but it is clear 

 that no absolute figure can be arrived at 

 in such a matter, except through labor- 

 ious inquiry. Taking, however, the 

 evidence derivable from our abattoirs it 

 may be stated that the number is rec- 

 koned at anything between one and 

 two per cent. If there should be one 

 animal in a herd suffering from tuber- 

 culosis of the udder, then it it quite 

 plain that the whole supply from such a 

 source constitutes a danger. Hence, on 

 arrival in a town, it must be dealt with 

 so as to destroy these and any other 

 germs, such as the organisms of measles, 

 diphtheria, fever, and others which may 

 be milk-borne, and to which milk pre- 

 sents a ready means of transmission and 

 propagation. 



In a modern dairy the milk is received, 

 and is then run through a strainer, of 

 which there are many designs in exist- 

 ence. From the strainer the milk falls 

 into a receiving tank, where the total 

 bulk is all mixed together up to the 

 capacity of the tank. From this tank it 

 falls into the receiver of a Pasteuriser, in 

 which it is heated to a temperature of 

 176° Fahr., which is a temperature be- 

 yond the thermal death point of patho- 

 genic germs. It is necessary, however, 

 to observe that this heating must be 

 done quickly, otherwise a certain taste 

 is imparted to the milk which is objec- 

 tionable. The taste may be due to the 

 caramelisation of the milk-sugar, and to 

 many palates this fact may render 

 the milk objectionable. Pasteurisers, 

 therefore, are made so that the milk 

 flows in at the bottom, and is elevat- 

 ed by means of rotating arms, which 

 cause the milk to run over a heated 



paroboloid surface, and is then dis- 

 charged at the top, and at once is 

 passed over a cooler. In modern dairy 

 practice it has been found desirable to 

 take advantage of the cooling effect of 

 water as a primary cooling agent, it 

 being quite obvious that where water is 

 available it is necessarily the cheapest 

 cooling medium. It is, therefore, wise 

 to provide what is termed a "primary 

 cooler," in which water is circulated, and 

 over which the milk flows after being 

 discharged from the Pasteuriser. If the 

 water passing through the cooler is at a 

 temperature of 52° Fahr., which is the 

 average temperature of well water in 

 the United Kingdom, then it is found 

 that by using certain forms of cooler, 

 the milk from the Pasteuriser can be 

 cooled to within 4° Fahr, of the water 

 temperature, that is to say 56° Fahr. 

 This end is best attained by means of a 

 conical cooler, as the milk falls upon the 

 upper flirtings in a certain volume, aud 

 as it reaches the bottom it broadens, 

 and thus a finer film is formed, which is 

 more easily cooled. Passing from the 

 primary cooler we then have a secon- 

 dary cooler, which is attached to the 

 refrigerating machine. The refrigerat- 

 ing machine is used to cool an unf reez- 

 able brine, which is circulated through 

 the secondary cooler at a temperature 

 approaching freezing point. The same 

 effect is obtained as with the water, 

 namely, that the milk flowing from the 

 primary cooler is at once cooled to with- 

 in 4° Fahr. of the circulating brine. 

 Thus, if we have brine circulating at a 

 temperature of 36° Fahr., we will get a 

 milk cooled down to 45° Fahr. At such 

 a degree milk is entirely inert, that is to 

 say, if there are any species of germs 

 present they will not develop, and if the 

 milk can be maintained at or about that 

 temperature there can be no doubt that 

 it will be in a pure condition, and practi- 

 cally germ free. Briefly speaking, that 

 is the description of the Pasteurising 

 process. As we see it is simple enough, 

 and is capable of large variation ; thus, 

 it may be worth while to interpose 

 what is described as a " regenerative 

 heater " between the Pasteuriser and the 

 cooler by which the excess of heat in 

 the Pasteurised milk is used to heat in- 

 coming fresh milk up to a certain 

 degree, and thus save fuel. I have not 

 found, however, that this particular 

 appliance has been received with much 

 favour. It certainly possesses advant- 

 ages which are incontestable, but it adds 

 to the plant necessary in a dairy, and 

 that is always an objection. 



The principal plant, as we see, in 

 connection with the production of germ- 

 free milk consists of steam and motive 

 power, a Pasteuriser, water supply for 



