326 THE CHEMISTRY OF DAIRYING 



and flavouring it. Larger quantities are used for " keeping " 

 butter than for that intended for immediate consumption ; but 

 it is the latter consideration, the flavour, that chiefly deter- 

 mines the amount of salt introduced. 



The composition of butter fat varies within certain limits 

 as is shown by the melting-point (p. 308) ; but it always 

 contains a relatively large amount of fatty acids of low mole- 

 cular weight, and especially butyric acid (p. 43). This is the 

 characteristic difference between butter and other fats, and the 

 more important methods of distinguishing between pure butter 

 and margarine are based on this principle. The acids of low 

 molecular weight are fairly soluble in water, and are more or 

 less volatile at the temperature of boiling water; the others 

 are practically insoluble and non-volatile. 



Hener's method is to estimate the insoluble acids, which 

 in pure butter fat rarely exceed 88 per cent, of the whole, 

 whereas in other fats they amount to 95 per cent, or more. 

 In the Reichert-Meissl test, it is the volatile acids that are 

 estimated. When carried out in the conventional manner, 

 from 24 to 30 c.c. of N/io alkali are required to neutralise 

 the acids distilled over from 5 grams of pure butter fat, 

 whereas not more than about i c.c. is required in the case of 

 other fats. The preliminary treatment, in both processes, 

 consists in saponifying the fat with alkali, and then decom- 

 posing the soap with dilute sulphuric acid. 



The melting-point, specific gravity, iodine number, and 

 saponification equivalent, may be used as confirmatory or 

 preliminary tests. 



Butter Colours. The popular demand for butter of a 

 uniform deeper yellow tint than it naturally exhibits has 

 rendered the use of artificial colouring matters both general 

 and practically necessary. Formerly, carrot juice was largely 

 used for this purpose, but turmeric, saffron, annatto, and, 

 occasionally in recent years, coal tar orange have been sub- 

 stituted for it. Annatto is most commonly used, and it is 

 probably the most suitable. It is a reddish yellow colouring 

 matter, derived from the pulp enclosing the seed of the 

 annatto plant, Bixa orellana^ a shrub which is indigenous to 



