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THE ESSENTIAL OIL OF HOPS, 



BY ALFRED C. CHAPMAN, F.I.C., F.C.S. 



HTHE yellow powder, or " lupulin," which is so readily separated 

 from ripe hop strobiles by mechanical means, constitutes, as is 

 well known, by far the most valuable part of the plant from the 

 brewing point of view. The " rubbing-down " test is, in fact, a recog- 

 nition of the truth of this, for the commercial value of a sample of hops 

 is known to depend largely on the amount of lupulin or " condition " 

 present, and this can be roughly judged by the degree of stickiness 

 experienced when the strobiles are rubbed between the fingers. This 

 yellow powder, if examined with a low magnifying power, will be found 

 to consist of small capsules of definite structure, which are in reality 

 superficial glands occurring on the external coating of the seeds, and 

 at the bases of the bracts or " petals." This is present to very varying 

 extents in different samples ; in old hops it may be as low as 3 per 

 cent., whilst in new and rich hops it may occur to the extent of 15 per 

 cent, or even more. This " condition " or " hop flour," as it is some- 

 times called, contains the essential oil, resins, wax, bitters, and 

 perhaps one or more alkaloids, but in this paper I propose to concern 

 myself with the first-mentioned constituent alone. The essential oil, 

 although boiling at temperatures much above the boiling point of 

 water, is nevertheless readily volatile with steam, and can therefore 

 be obtained from the hop strobiles (or from the separated lupulin 

 itself) by boiling with water in a still, the essential oil passing over with 

 the steam, and being condensed by suitable means. Owing to its very 

 slight solubility in water, it is found floating on the surface of the dis- 

 tillate, and may be recovered either by mechanical separation or by 



