AROMA OF HOPS: A STUDY OF THE VOLATILE OIL 
WITH RELATION TO THE GEOGRAPHICAL SOURCES 
OF THE HOPS 
By Frank Rabak, 
Chemical Biologist, Drug-Plant and Poisonous-Plant Investigations , 
Bureau of Plant Industry 
At the present time the principal method for distinguishing the kind 
and source of hops is by means of their appearance and odor. This must 
necessarily be an uncertain and crude method because of the inability of 
individuals to differentiate accurately between similar odors, and, hence, 
it can serve only to determine extremes in the quality of the hops. If, 
therefore, a scientific method based on the actual properties of the hops 
could be worked out, it would be considerably more satisfactory and 
accurate. Since the aroma, which is conceded to be an important factor 
in judging hops, can be readily concentrated in the volatile oil, it was 
thought that a systematic comparison of the properties of oils distilled 
from hops obtained from the various hop-producing countries of the 
world and grown during different seasons would give information which 
would be valuable not only as a means for judging the quality but also 
to determine the geographical source of the hops. 
FACTORS WHICH INFLUENCE THE AROMA OF HOPS 
Since altitude, light, hygrometric conditions, and the composition of 
the soil affect the composition of the volatile oils of thyme, lavender, 
rosemary, and peppermint (Jeancard and Satie, 1909; Bonnier, 1894; 
Lamothe, 1908; Mossier, 1912) 1 , it may be easily seen that hops grown in 
separated localities under different conditions of climate and soil may be 
widely different in aroma and may produce volatile oils with distinct 
and constant variations in their chemical properties. This assumption 
is practically substantiated by Briant and Meacham (1896), who discuss 
the influence of climate, ripeness, soil, drying, and general manipulation 
on the value of hops. The amount of rain and sunshine alters the con¬ 
ditions of ripening, and the different degrees of ripeness have a decided 
effect upon the quality of the hops. Regarding the influence of soil upon 
the quality of the product, these authors state: 
The effect of soil is, however, undoubtedly very great, for it comes within our 
experience that on two farms in the same neighborhood but with different soils the 
hops grown upon one are year after year of a decidedly superior character both as 
regards resins and flavor, to those on the other, although both are farmed in similar 
manner and with practically the same climatic conditions. 
1 Bibliographic citations in parentheses refer to “ Literature cited," p. 158-159. 
(«S> 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D. C. 
Vol. II, No. * 
May 35, 1914 
G— si 
