PART ii BUTTER 



When butter is kept, it undergoes a decomposition which 

 makes it useless as food. This rancidity of the butter, as it is 

 called, is due to the splitting up of the fat by certain micro- 

 organisms into glycerine and free fatty acids. Butter also 

 sometimes acquires a tallowy flavour, which is the result of an 

 oxidation process influenced by air and light. 



The specific gravity of slightly salt butter made from sour 

 cream is on an average 0*9625 at 15 C., according to V. Storch's 

 investigations. 1 Fleischmann 2 gives the average specific gravity 

 of unsalted butter as 0*9437 at 15 C. The melting point and 

 point of solidification of butter lie very near to the corresponding 

 numbers obtained for pure butter fat. Prof. V. Storch, of 

 Copenhagen, has studied the inner construction of butter very 

 completely, and through his investigations an insight has been 

 gained into its remarkably peculiar structure. 



Butter does not consist of fat alone, but contains other 

 substances which come from the milk. In round figures, it may 

 be said that butter is composed of 84 per cent, fat and 16 per 

 cent, of other substances, of which about 13 per cent, is water. 

 The liquid present in butter which contains small quantities 

 of other milk constituents, such as albumin, milk-sugar, and salts 

 (also some added common salt), is called brine. It is this 

 clear liquid which is to be seen in the form of small, clear drops 

 on the freshly-cut surface of butter. Storch has shown, with 

 the help of the microscope, that brine is present in butter in 

 the form of an immense number of minute drops, the number 

 and size of which vary considerably, but are in very close con- 

 nection with the appearance and consistency of the butter. 

 The number of these small drops of liquid in each cubic milli- 

 metre in butter varies from 2*5 to 13 millions, and, as regards 

 size, the majority of the drops do not reach 0*01 rnm. in 

 diameter, and only a small number exceed 0*05 mm. Occasion- 

 ally single drops of much larger diameter are to be found. 

 Butter may therefore be regarded as an emulsion of brine in 

 butter-fat. 



To investigate the construction of butter, a small piece about 

 the size of a pin-head is taken, and carefully spread out by 

 pressing it between the slide and cover-glass. The microscopic 



1 36' e Beretniny fra den Kgl. Vet- og Landbohojskoles Lab. for lando'konom. 

 Forso-g, p. 121. 



2 Lehrbuch der Milchwirlschaft. Fourth Edition. Leipsic, 1907, p. 266. 



K 2 



