STRUCTURE OF THE HOP CONE. 281 



renders the beer aromatic, and produces the agreeable odour 

 and flavour of the beverage. Once absorbed by the beer it is 

 no longer volatile, and probably passes into solution in the 

 alcohol formed during fermentation. 



The obnoxious smell, " like rotten cheese," developed 

 when hops are exposed to the air for a long time, does not, 

 as hitherto supposed, result from oxidation of the hop oil to 

 valerianic acid, the malodorous constituent being, as Chap- 

 man ^ has shown, an oxidation product of other constituents, 

 probably the soft resin.^ 



On prolonged exposure to the air hop oil absorbes oxygen, 

 and solidifies to a hard resinous mass devoid of smell. 



By fractional distillation Chapman separated the oil into 

 three distillates, the first of which proved to be a mixture of 

 two unsaturated hydrocarbons, the second a colourless oil 

 with an odour of geranium, and the third a sesqui-terpene, 

 to which Chapman gave the name humulene. 



From the researches of Chapman and Meacham it also 

 appears that, contrary to previous assumptions, hop oil has 

 no antiseptic powers, a circumstance which throws doubt 

 ■on its alleged property of restricting fermentation. 



Undoubtedly the chief function of hop oil in beer is to 

 impart aroma, and Fruwirth was therefore quite right in 

 ■saying that " all other effects of hopping can be produced by 

 using inferior kinds, but to develop a fine aroma in beer, 

 best hops are indispensable ". 



Hop resins. — According to Hayduck these are three in 

 number, the a, /3 and 7 resins. The first-named, the a resin, 

 can be precipitated from the alcoholic solution of ethereal 

 hop extract by lead acetate. The /3 resin, after the removal 

 of the residual lead salt, re-solution in ether, agitation with 0'5 



1 Buugener believes it to result from oxidation of the bitter principle of 

 the hop. 



^ Zeitschrift filr das gesammte Brauwesen, 1898, Nos. 26 and 44. 



