CHAP. v. KANCIDITY IN BUTTER. 315 



vary from 9 to 19 per cent. Water being liquid at all ordinary 

 temperatures, the more there is present the softer the butter ; in the 

 summer too much is generally left in, which makes the butter soft, 

 while in the winter butter frequently contains far less water, and is too 

 hard. The finer the granules are when brought in the churn, the 

 more water will the butter retain, and no amount of subsequent work 

 on the butter-worker will get rid of it. In summer, therefore, it is 

 necessary to collect the butter into larger granules than in winter, so 

 as to exclude water. And before working it is essential to place the 

 granular butter in a cooling box, not merely to lower the temperature 

 and hence harden the granules, but mainly to allow the excess of 

 water to drain away. In the \yinter smaller granules and more water 

 are advisable." 



The substance, remarks Duclaux, which is taken out of the churn 

 is not pure butter fat, but consists of this material mixed with a little 

 of the serum or whey, small quantities of casein, and milk sugar, as 

 well as phosphate of lime and other mineral salts. In addition, there 

 is water, the quantity of which depends upon the method which has 

 been employed. M. Chevreul's investigations have shown that, in the 

 fresh state, pure butter fat consists only of glycerides, that is, of 

 compounds of glycerin with acids, the latter called fatty acids because 

 they enter into the composition of fats. Some, as stearic, margaric, 

 and oleic acids, have the appearance of fat, whilst others are liquids 

 which dissolve in water. The fatty acids with a fat-like appearance 

 were the first known, because they are relatively easy to isolate and 

 are insoluble in water. Although all kinds of butter, notwithstanding 

 differences in. breeds and foods of cattle, contain approximately the 

 same proportions of the same glycerides, yet there are, within very 

 restricted limits, marked variations. The glycerides which have been 

 found in butter are palmitin, olein, stearin, margarin (probably a 

 mixture of palmitin and stearin), caprylin, caprin, caproin, and 

 butyrin. The principal ones are present in about the following 

 percentages : 



Stearin and palmitin . . 62'8 



Olein 27'8 



Caprylin and caproin 6 - 



Butyrin 3'4 



100-0 



Left to itself fresh butter gradually loses its fine and delicate 

 flavour and becomes rancid. What happens chemically is this. In 

 rancid butter, there appears in the free state several strong-smelling 

 acids, one of which, butyric acid, has received its name because its 

 odour is precisely that of rancid butter. Another, caproic acid, is 

 named in reference to the fact that its odour calls to mind that of the 

 goat (Lat. capra, a goat). The least traces of these acids in the 

 free state powerfully affect both the flavour and the odour of butter, 

 and it is primarily to their presence that butter owes those unpleasant 

 qualities which are conveyed in the description rancid. The circum- 



