284 Agricultural Chemistry. 



of a ripened cream is driven out by the agitation. These two 

 factors give rise to the pressure observed within the churn. 

 Churning should always be stopped as soon as the butter appears 

 in fine grains. This allows a more complete separation, by wash- 

 ing, of the butter-milk, and removes one of the important factors 

 in the production of mottles in butter. Further, the more com- 

 pletely the butter-milk is removed, the better will be the keeping 

 qualities of the butter. 



Freshly separated cream is sometimes churned, but it is gen- 

 erally admitted that the best flavor and aroma for butter can 

 only be obtained by the use of properly ripened cream. This is, 

 cream to which lactic acid organisms have either gained access 

 spontaneously, or, as is preferred in modern practice, have been 

 added in the form of a ''starter" of sour skimmed milk or some 

 pure culture of the lactic organisms. The degree of ripeness 

 which is probably best, corresponds to about 0.5 per cent of lactic 

 acid ; but the acidity most suitable depends to some extent upon 

 the flavor desired in the butter. If the cream is over ripe, the 

 casein present may be hardened and on churning is found as 

 white specks or flakes in the butter, spoiling its appearance and 

 endangering its keeping qualities. 



Salt is usually added to butter, serving both as a condiment 

 and as a preservative, the proportion varying from a mere trace 

 to 5 or 6 per cent. 



Composition of butter. The main constituent is of course 

 fat, but in addition, water, casein, milk sugar and ash are also 

 present. The amount of fat is usually about 80 to 86 per cent, 

 water about 11 to 12, casein from 0.6 to 1.5 and salt from 0.1 

 to 4.0 per cent. Under the present pure food law of the United 

 States it is unlawful to sell butter containing more than 16 

 per cent of water. So called "milk-blended butters " prepared 

 by kneading butter in milk, usually contain an excessive quantity 

 of water and a high proportion of casein. 



Renovated butter. In this country old and rancid butter is 

 sometimes converted into what is known as " renovated, " "pro- 



