May as. 1914 
Aroma of Hops 
119 
Considerable variation exists in the yield of oil from the different Cali¬ 
fornia hops, not only among the different samples of any one season, 
but also among the same hops during successive seasons. The average 
yield of oil from all the California hops during 1907, 1908, and 1909 was 
0.32 per cent. Perkins, Cosumne, and Ukiah hops yielded oils which 
averaged very well during the three seasons. The oil from the Wheat- 
land hops was somewhat below the general average. 
The Oregon hops which were distilled during the four successive years 
showed an average oil content of 0.29 per cent, which is a trifle less than 
the average California sample. 
The New York hops, with an average during the four years of 0.192 
per cent of oil, were noticeably lower in oil content than any of the other 
hops distilled. Only in one year, 1906, did the yield approach that of the 
California, Oregon, Washington, or the imported hops. 
The Washington hops, which were distilled only during two seasons, 
appear to possess the highest percentage of oil, the average being 0.37 
per cent. 
The imported hops distilled from the crops of 1906, 1907, 1908, and 
1909 showed an average yield of 0.31 per cent of oil, considerable change 
appearing from season to season. 
When distilled for a period of more than two seasons, all the hops 
showed considerable fluctuation in the yield of oil. Named in the order 
of their average yield the hops group themselves as follows: Washington, 
California, imported (Saaz), Oregon, and New York. 
This variability in the oil content may be ascribed to varying condi¬ 
tions of climate and soil, as well as to ripeness and drying of the hops, 
which would affect the formation of the oil in the plant. Slight differ¬ 
ences in yield of oil would not necessarily influence the quality, since the 
same proportion of odoriferous constituents may still be present. 
PHYSICAL PROPERTIES OF THE VARIOUS OILS 
The physical properties of the oils permit a somewhat better means for 
comparison, and therefore a record was made of the color, odor, and taste 
of each of the oils mentioned. Differences in color are, of course, readily 
noted, but differences in odor and taste are considerably less noticeable, 
because of the difficulty with which the senses of smell and taste distin¬ 
guish closely related substances. The specific gravity, refractive power, 
and solubility, each of which can be accurately measured, are of much 
greater importance, although even these properties are usually entirely 
inadequate for detecting constant differences. However, as they are 
affected by the constituents of the oils they are sometimes of considerable 
value. In all cases the oils were too dark to permit making determina¬ 
tions of the optical rotation, which is often useful in detecting certain 
differences in composition. The tabulation shows the physical proper¬ 
ties of the various hop oils distilled during the seasons 1907, 1908, and 
1909 (Table II). 
