May 25. 1914 
Aroma of Hops 
157 
remains lower from year to year, practically every sample under obser¬ 
vation possessing an exceedingly low ester value. The oils from the 
California hops are both physically and chemically very similar from 
season to season. Those from the various sections of California show no 
important differences in their properties during any particular season, 
the curves showing considerable parallelism. The Oregon and Wash¬ 
ington oils are very similar in their properties, but differ somewhat from 
the California oils. The New York oils seem to be the most closely 
related to the foreign oils in all properties, with the exception of the 
ester content, which is considerably higher. From the standpoint of 
the increasing ester content the various oils arrange themselves in the 
following order: Imported, California, Washington, New York, and 
Oregon, the three latter being very closely related. (See fig. 1.) 
No general conclusions can be drawn regarding the possible superiority 
of any particular oil as compared with any of the other oils. Whether 
high or low ester content denotes richness or poorness in the quality of 
the hops, or vice versa, can not be definitely stated. Suffice it to say 
that from the results obtained it is clear that the geographical source of 
hops may be indicated by the ester numbers of the oil distilled from the 
hops, since the experiments show that the ester numbers of the oils from 
hops of any particular source or season are very similar. 
REVIEW OF PREVIOUS CHEMICAL INVESTIGATIONS OF THE ARO¬ 
MATIC CONSTITUENTS OF HOPS 
Reference to the odor of hops was made in literature as early as 1819. Loiseleur 
Deslongchamps (1819) mentioned the cones of hops as possessing a bitter taste and a 
strong odor resembling garlic. Hanin (1819) reported that the yellow powder of hops 
was very tasteful, very odorous, and inflammable, with all the characteristics of a 
resin. Ives (1821) in an investigation of the properties of hops, referred to the yellow 
powder of the cones as “lupulin,” which, he stated, contained the bitter principle 
and the aromatic flavor of the hops. Working with samples of 1 dram to 2 ounces 
of lupulin, no volatile oil was separated, but the aqueous distillate possessed the 
odor of hops. The following year Payen and Chevalier (1822) found that by dis¬ 
tilling the yellow powder (lupulin) a volatile oil was obtained which had the char¬ 
acteristic odor of hops. 
The first investigation concerning the nature of the oil was made by Wagner (1853) 
who distilled the oil directly from the hops instead of from the lupulin. The oil 
was described as being bright brownish yellow in color with a srtong odor of hops and 
a burning, slightly bitter taste. The solubility of the oil in water was sufficient to 
impart a decided hop odor, the solubility being influenced by dextrin, sugar, hop 
extract, etc. It was stated that the oil contained a terpene, which was likened to 
camphene, and also an oxygenated constituent, isomeric with bomeo camphor. 
According to Personne (1854), lupulin when boiled with water produced a vola¬ 
tile oil and a nonvolatile residue. Valerianic acid was identified among the volatile 
products; also an oxygenated compound called “valerol.” Some years later Kuhne- 
mann (1877) distilled hops with steam and obtained an oily substance which he 
called “hop oil.” The oil was described as being a mixture of hydrocarbons and 
oxygenated compounds, the latter consisting of alcohols and acids. Ossipow (1883) 
41217 0 —14-6 
