UNITED STATES DEPARTMENT OF AGRICULTURE 



SLfP^mTU 



BULLETIN No. 282 



Contribution from the Bureau of Plant Industry 

 WM. A. TAYLOR, Chief 



JU^°-^r< 



Washington, D. C. 



PROFESSIONAL PAPER 



August 11, 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. 

 Introduction 1 



Preparation of the hops studied 2 



Changes in physical appearance 3 



Moisture content and changes in the propor- 

 tion of soft and hard resins 4 



Changes in the composition of the soft resins . . 10 



Chemical values of the soft resins 15 



Summary 18 



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, 1 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, 2 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. 



i 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. Bui. 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. Tha 

 soft resins, or so-called bitter acids, are a principal factor in determining the commercial value of hops. 

 98657°— Bull. 282—15 1 



