168 Butter Churning. [Sept., 



these we have a natural and intelligible source of differences also 

 in the quality and consistence of the butter. 



But from the same milk, by the absorption of oxygen in greater 

 or less abundance, a harder or softer butter may also be produced, 

 and in this tact satisfactorily and chemically explained, we have 

 the key to many practical anomalies. It may also enable us here- 

 after to arrive at a modification of the usual mode of churning, by 

 which butter of the firmest consistence may more frequently be 

 obtained. 



The chemical influence of the air in the process of churning 

 has often been suspected, but the })recise way in which it might 

 actually influence the quality of the butter has not previously been 

 pointed out. 



Influence of the air en the process of churning hy ordinary me- 

 thods. 



In connection with the subject of the preceding article, and to 

 make the whole circumstances more clear, I shall here consider 

 also what sei ies of changes usually take place in the process of 

 churning by the ordinary methofls. 



It is conceded that the presence of air and oxygen, or their re- 

 newal, aie not necessary to the churning of milk or butter. It 

 can be completely effected by prolonged agitation inclose vessels. 

 When this is the case therefore, the quality of the butter formed, 

 and the changes which the milk undei goes, are entirely independ- 

 ent of any chemical influence from without. 



But in ordinary churning the air is, I believe never excluded. 

 If, therefore, a probable chemical influence of the air in churning, 

 or upon the results of the churning, can be pointed out, it is rea- 

 sonable to suppose, in the absence of proof to the contrary, that 

 such an influence is really exercised. Let us therefore consider 

 the chemical changes which take place during this operation, and 

 the influence which the presence or absence of the air may have 

 upon the result. 



1. Sensible changes inhich always accompany the churning of 

 milk. — V\ hen sweet milk, or cream, is churned, two changes are 

 obvious to every one; the milk becomes sour, and the butter is 

 separated in a solid form. The first of these — the souring — is due 

 to the change of the sugar of milk into lactic acid. This is a 

 chemical change, but it requires neither the addition nor substrac- 

 tion of any new matter. The constituents of the milk sugar, by 

 a mere new arrangement among themselves form the acid of milk. 

 The second change — the separation of the butter in a solid form, 

 is owing to the breaking u[) of the envelopes of the globules of 

 fat, and the mutual adhesion of these globules when they come in 

 contact with each other. This change may be regarded as en- 



