

Contribution from the Bureau of Plant Industry: > 
WM. A. TAYLOR, Chief 


Washington, D. C. PROFESSIONAL PAPER August iets 1915 
A STUDY OF THE SOFT RESINS IN SULPHURED AND UNSUL- 
PHURED HOPS IN COLD AND IN OPEN STORAGE. 
By G. A. RUSSELL, 
Expert, Drug-Plant and Poisonous-Plant Investigations. 

CONTENTS. 
: Page. Page 
LENRROC IDO) 5 ae coe ban Sas SocEdee Seu EEeaeaerae 1 | Changes in the composition of the soft resins. . 10 
Preparation of the hops studied........-.. 2 | Chemical values of the soft resins............ 15 
Changes in physical appearance..-...-....-.-- Oily OURTINIATYi~ Sosa tp opeie icleio cele canine ec meee 18 
Moisture content and changes in the propor- 
tion of soft and hard resins...........-...-.- 4 
INTRODUCTION. 
During the past decade the soft resins of hops have been the sub- 
ject of numerous investigations which have dealt almost exclu- 
sively with the percentage of yield and the methods of extraction. 
With the exception of the work of Fischer,’ no statements have been 
found in the literature to show that recognized chemical methods 
have been used to determine the changes which occur in the soft 
resins of hops subsequent to harvesting. The effect of refrigeration 
on the physical condition and on certain chemical constituents of sul- 
phured and unsulphured hops has been studied by Stockberger and 
Rabak,? who gave special consideration to the changes which occur 
in the volatile oil. Aside from the changes noted by these authors, 
extensive modifications also occur in the soft resins of hops, the 
character of which may be determined through the use of reliable 
analytical methods. 
1 Fischer, Alfred. Analysis of hops as a basis for their valuation. _In Pure Products, v. 8, no. 10, 
p. 536-538, 1912. 
2 Stockberger, W. W., and Rabak, Frank. Some effects of refrigeration on sulphured and unsulphured 
hops. U.S. Dept. Agr., Bur. Plant Indus. Bul. 271, 21 p. 1912. 
Note.—This bulletin presents the results obtained from experiments conducted to determine the extent 
and character of the changes in the soft resins in hops under varying conditions of curing and storage. The 
soft resins, or so-called bitter acids, are a principal factor in determining the commercial value of hops. 
98657°—Bull. 282—15——1 
