66 



of the constituents are altogether insufficient for the purpose of 

 detecting them. The Californian oil " No. 6 " for example, yielded 

 the same compounds as the Bavarian and English oils, and the 

 differences in their odour must have been due, partly perhaps, to the 

 different proportions in which the above constituents existed ; but 

 also, probably, to the presence of very small quantities of other 

 fragrant substances, the separation of which in a state of purity was 

 rendered impossible by the nearness of their boiling points, and by 

 the great expense attending work with large quantities of the oil. 

 We now come to the important question : What part does the 

 essential oil play in brewing procedure ? By the older authorities it 

 was stated that the oil acted both as a flavouring and as a preserva- 

 tive agent, and that its role was consequently a most important one. 

 With the latter point I propose to deal shortly, and will first discuss 

 the question of flavour. As was pointed out at the commencement 

 of the paper, the oil of hops is freely volatile with steam, and 

 consequently little or none can remain in the wort at the end of the 

 boiling period. The fragrant odour of the air for a considerable 

 distance around a brewery when the wort is being boiled is 

 sufficient proof of this escape of oil. On this point the following 

 experiment may be of interest : 



Small quantities of oil were added to brewery wort which was 

 boiled for periods varying from half an hour to two hours in large 

 glass flasks. Extraction experiments made at the end of this period 

 showed that even after half an hour 80 per cent, or more of the oil 

 had volatilised with the steam, and that the great bulk of the 

 remaining 20 per cent, had become converted into a sticky resinous 

 mass. It may, therefore, be regarded as certain that little or no 

 unchanged volatile oil can possibly remain in the copper at the end 

 of boiling. 



Even when a portion of the hops are added, as is often done 

 about half an hour before turning out, it is practically certain that 

 none of the volatile oil is left ; and, it may be asked, to what, then, 

 is the hop flavour due ? It has already been pointed out that the 

 oil readily oxidises and polymerises when exposed to the air, 

 becoming viscous and resinous. This resin (which must not be 



