on Milk and Milk-Products. 
397 
organisms, soon caused the coagulation of the milk, while the 
milk mixed with the scum of the latter remained apparently 
unchanged for ten days. It does not appear that the micro- 
organisms, which must be supposed to have played the pro- 
minent part in causing the decomposition of butter, were 
investigated any further, and it is therefore impossible to 
identify them with any of those micro-organisms previously 
described. 
According to what has been said above, we must assume that 
the keeping quality of butter depends, if not entirely, certainly 
in the first place upon the state of the contained butter-milk. It 
might, then, appear advisable to remove all the butter-milk ; but 
this is not only a practical impossibility, but it would also 
deprive the product of its proper character. It is, however, 
certainly desirable to expel as much of the butter-milk, by 
washing and kneading the butter, as can be done without 
injuring its quality and deteriorating its value, and further to 
take precautions that what butter-milk is left is present in a 
state in which it can do the least injury. This is the case, for 
instance, if sweet material is churned. Circumstances are less 
favourable with regard to sour churning material ; but there are 
different degrees of acidity, which have great influence on the 
keeping quality of the butter. As long as the milk or cream to 
be churned is only slightly sour, there will be no difficulty in 
breaking up the gelatinous casein into particles of the minutest 
size ; but if the material has been allowed to reach a high 
degree of acidity, the casein will partially have been precipi- 
tated in small lumps, which are not broken by the churning 
process, and when included in the butter cannot be removed by 
washing or working, and form a centre of decomposition which 
will soon set in and progress rapidly. 
One mode of preservation, viz., destroying micro-organisms 
by the application of heat, is entirely excluded in the case of 
butter. Low temperatures have a very good effect, but their 
application meets with great difficulty in practice. There is 
one way, however, left, which in a great number of cases answers 
the purpose exceedingly well, and is in no way objectionable, 
viz., to make use of the preservative qualities of common salt. 
Butter salt should if possible consist of fine crystals, congregated 
in little pyramids or funnels. Such salt, when worked into fresh- 
churned butter, easily dissolves in the buttermilk, gathering the 
latter in drops large enough to run off, thus removing a large 
proportion of buttermilk, and guarding the remaining portion 
against further decomposition. It may be observed here that 
it has been found that salicylic acid causes butter to acquire a 
tallowy taste. 
