68 



some valeric ester, and it is far from improbable that these esters, 

 under the conditions of ordinary hop storage (that is, exposed to the 

 combined action of moisture and air), may undergo slight hydrolysis 

 with liberation of traces of the two fatty acids, isovaleric and 

 isononoic, which have very similar odours, resembling old cheese or 

 rancid butter. Experiments made with the " soft resins " extracted 

 from the hops by means of light petroleum showed that isovaleric 

 acid in quantity was formed when these were submitted to the action 

 of an alkaline solution of potassium permanganate or to other 

 oxidising agents. Although there is no evidence that these resins 

 can give rise to isovaleric acid under the ordinary condition of 

 aerial oxidation, it is possible that they may, to some slight extent, 

 contribute to the cheesy odour, and the same may be true of the 

 bitter principle described by BUNGENER. 



Numerous experiments were made, in which the oil was 

 submitted to the action of such chemical oxidising agents as chromic 

 acid, potassium permanganate and nitric acid, the oxidation products 

 being separated, purified and identified. In this way acetic, valeric, 

 unsymmetrical dimethyl succinic, succinic and isononoic acids were 

 obtained when chromic acid was employed, whilst with potassium 

 permanganate all the above oxidation products were yielded except 

 dimethyl succinic acid, and oxalic acid was found in considerable 

 quantity when dilute nitric acid was used. 



From the experiments of which a brief outline has been given 

 in this paper it will be seen that the essential oil of hops plays a 

 less important part in the brewing process than was supposed by 

 earlier investigators and authors. It must not, however, be thought 

 that for this reason the character of the essential oil, as indicated 

 by the aroma of the hops, is a point which the brewer may neglect, 

 since the non- volatile flavouring resin, to which reference has been 

 made above, develops to a very considerable extent the peculiarities 

 of odour exhibited by the fresh oil itself. There is very little doubt 

 that any unpleasantness in the oil will be communicated to the 

 resin, and so in turn to the beer. It is, moreover, one of the surest 

 guides to the general value of a sample of hops, where reliance is 

 placed solely upon a physical examination. The short biblio- 



