564 INFLUENCE OF THE CHEESY MATTER. 



short exposure to the air it alters in some degree, and acquires the power 

 of transforming milk sugar into lactic acid. Hence, as we have seen, the 

 milk ])egins speedily to become sour. Further changes follow, and, 

 among other substances, butyric acid is formed. 



In butter the same changes take place. The casein alters the suga? 

 and the fatty matters, producing the butyric and other acids, lo which its 

 rancid taste and smell are lo be ascribed. 



In the manufacture of butter, therefore, it is of consequence to free it as 

 completely as possible from the curd and sugar of milk. This is done 

 in some dairies by kneading and pressing only ; in others, by washing 

 with cold water as long as the latter comes off' milky. The washing 

 must be th« most effective method, and is very generally recommended 

 for butter that is to be eaten fresh. In some dairies, however, it is care- 

 fully abstained from, in the case of butter which is to be salted for long 

 keeping. 



There are two circumstances which, in the case of butter that is to be 

 kept for a length of time, may render it inexpedient to adopt the method 

 of washing. The water may not be of the purest kind, and thus may 

 be fitted to promote the future decomposition of the butter. Sprengel 

 says that the water ought to contain as little lime as possible, because 

 the butter retains the lime and acquires a bad taste from it. 



But the water may also contain organic substances in solution — vege- 

 table or animal matters not visible perhaps, yet usually present even in 

 spring water. These the butter is sure to extract, and they may mate- 

 rially contribute to its after-decay, and to the difficulty of preserving it 

 from rancidity. 



Again, the washing with water exposes the particles of the butter to 

 the action of the oxygen of tha atmosphere much more than when the 

 butter is merely well squeezed. The effect of this oxygen, in altering 

 either the fatty matters themselves or the small quantity of casein which 

 remains mixed with them, may, no doubt, contribute to render some but- 

 ters more susceptible of decay. 



3°. But the casein, after it has been a still longer time or more fully 

 exposed to the air, undergoes a second alteration, by which its tendency 

 to transform the substances with which it may be in contact, is consi- 

 derably increased. It acquires the property also of inducing chemical 

 changes of an(^er kind, and it is not improbable that the more un- 

 pleasant smelling capric and caproic acids may be produced during this 

 period of its action. 



In the preservation of butter, therefore, for a length of time, it is of 

 indispensable necessity that the air should be excktded from it as com- 

 pletely as possible. In butter that is to be salted also, it is obvious that 

 the sooner the salt is applied and the whole packed close, the better and 

 sweeter the butter is likely to remain. 



4°. The action of this cheesy matter, and its tendency to decay, are 

 arrested or greatly retarded by the presence o^ saturated solutions of cer- 

 tain saline and other substances. Of this kind is common salt, which is 

 most usually employed for the purpose of preserving butter. Saltpetre, 

 also, possesses this property in a less degree, and is said to impart to the 

 butter an agreeable flavour. A syrup or strong solution of sugar will 

 likewise prevent both meat and butter from becoming rancid. liike salt- 



