RESINS 



53 



are employed for various purposes, while in the case of the hop 

 the value of the plant depends very largely upon the amount of 

 resins, which occur in this case also in association with a terpene 

 (CioHjc), "hop-oil." This oil gives the characteristic aroma and 

 flavour to the beer, while the bittering and preservative properties 

 of hops are known to reside in the resins. 



32. Quantitative determination of Resins in Hops. 



There are two varieties of resins present in hops : 

 "soft" resins, soluble in petroleum ether, and "hard" 

 resins, which can be extracted with ordinary ether 

 after the removal of the "soft" resins. According to 

 Briant and Meacham, it is the " soft " resins alone that 

 are preservative in their action. 



The quantitative estimation of the "soft" resins 

 is performed as follows : — ¥vom 3 to 5 grams of 

 hops are weighed out and carefully placed in a 

 cartridge of filter paper that has been previously 

 extracted with petroleum ether. The cartridge and 

 contents are then extracted for twenty-four hours in 

 a Soxhlet apparatus, using petroleum ether of B.P. 

 40°-5o° C. 



The ethereal extract is then drained from the 

 cartridge into the extraction flask, and the ether 

 evaporated off in the water-bath, the ether being 

 conveniently condensed and collected in the Soxhlet 

 apparatus, from which the extracted cartridge has 

 been removed. The flask and residue is next trans- 

 ferred to a steam oven, dried for six hours in the steam 

 oven, and weighed. 



Approximate percentages of" soft " resins in different 

 varieties of hops are as follows : — 



Fuggles, . . . 10 to 1 1 

 East Kent Goldings, . 1 1 to 1 3 

 Canterbury Whitebines, 1 2 to 1 5 



Holledaus, . . 16 to 18 



Oregons, . . . 16 to 17 



D 2 



