May 25, 1914 
Aroma of Hops 
155 
points of certain sesquiterpene alcohols correspond very closely to these. 
Thus, cedrol, the sesquiterpene alcohol obtained from cedar-wood oil, 
boils at 282°, and santalol, obtained from oil of santal wood, boils at 
301 0 C. The possible presence of sesquiterpene alcohols is also indicated 
by the low carbon content of these fractions, as shown by the elementary 
analysis. In order to positively identify the sesquiterpene humulene 
in oil of hops, three high-boiling fractions (225 0 to 245 0 , 245 0 to 260°, 
and 260° to 275 0 C.) of several unsaponified oils were used. Petroleum 
ether solutions of these fractions were treated with a concentrated solu¬ 
tion of sodium nitrite with an equal volume of glacial acetic acid added 
in small portions and vigorously agitated, the mixture being kept well 
cooled. In fraction 245 0 to 260° there appeared blue needle-shaped 
crystals, which melted at 125 0 C. This is in accordance with the melting 
points of humulene nitrosite recorded by Chapman (1895b, p. 783) and 
by Fichter and Katz (1899), which are, respectively, 120 0 and 127 0 C. 
The characteristic blue coloration of the fraction from which the crystals 
were obtained was produced in each case. 
APPROXIMATE COMPOSITION OR THE OIL 
From the foregoing analysis of the oil of hops it appears that it has 
approximately the following composition: 
Free Acids. —Chiefly valerianic, with traces of formic, butyric, and heptoic acids. 
Combined Acids (in form of esters ).—Chiefly heptoic (oenanthylic) and nonoic 
(pelargonic) and somewhat smaller quantities of octoic (caprylic), some decylic 
(caprinic) and undecylic acids, with traces of formic and acetic acids. 
Aldehydes. —Formaldehyde in the lowest boiling fraction. 
Hydrocarbons. —Myrcene (olefinic terpene), 30 to 50 per cent. Humulene 
(sesquiterpene), 15 to 25 per cent. 
Esters. —Chiefly heptoic, octoic, and nonoic acid esters of the alcohol myrcenol, 
to the extent of 20 to 40 per cent. From the ester number (44) of the oil in question 
the amount of esters calculated as the heptoic-acid ester of myrcenol was found to 
be 21 per cent. If calculated as the octoic or nonoic acid esters, the percentage 
would be considerably augmented. 
Alcohols. —Probably myrcenol and a small proportion of sesquiterpene alcohols. 
RELATION OF THE VOLATILE OIL TO THE SOURCE OF THE HOPS 
From the data presented it is clearly evident that the geographical 
source of hops has a pronounced effect upon the volatile oil and hence 
also upon the odor of the hops. The oils distilled from hops of different 
origin have been shown to possess like constituents, which, however, exist 
in sufficiently varying proportions to impart a decided difference to the 
properties of the oil. These differences appear to be constant from season 
to season, not only in the physical properties but also in the more import¬ 
ant chemical properties. Most conspicuous among the chemical prop¬ 
erties is the ester value, which is closely related to the odor. The ester 
content is the most influential factor in modifying the odor of the oils and 
