84 



low content of soft resin. Certain experiments made by REMY as to 

 the influence of kiln drying on hops, showed that a considerable 

 proportion of the soft resin present in the fresh hops is converted 

 into hard resin during drying in the air. 



In the course of investigations made by LINTNER and the author, 

 and relating to the bitter principles of hops, an attempt was made 

 to estimate the /?-bitter acid by titration of a hop extract. Since the 

 resins are themselves acid in character, it might be possible by this 

 method to find the total quantity of resin present. 



LiNTNER 1 gives the following details: 10 grms. of hops are 

 placed in a ^-litre flask, graduated at 505 c.c. (5 c.c. is the volume of 

 the hops), and extracted for eight hours with 300 c.c. of petroleum 

 ether (b.p. 30-50 C.) under an inverted condenser. The time of 

 extraction eight hours was fixed upon as necessary from the 

 result of special experiments, although the bulk of the resin is 

 extracted in two hours. The flask is then filled up to the 505 c.c. 

 mark with petroleum ether at 1 7-5 C., and the liquid filtered as rapidly 



as possible so as to prevent solution of the a-resin. 100 c.c. of the 



N 

 extract are titrated with potassium hydrate. As the alcoholic 



potash does not mix with the petroleum ether, 80 c.c. of strong alcohol 

 must be added before titration, together with 10 drops of phenol p- 

 thalein solution (i in 100) as indicator. A blank experiment must 

 be made to determine the acid in the ether and alcohol, and a cor- 

 rection applied. Since one molecule of alkali neutralises one mole- 

 cule of lupulinic acid (molecular weight 400), the volume of alkali 

 consumed multiplied by 0^4 equals the weight of acid present. 



Dr. HEIM 2 examined 15 different hops by LINTNER'S method, 

 the samples being supplied by the firm of F. J. BARTH & WEIGMANN, 

 in Lauf. With most varieties the results ranged within compara- 

 tively narrow limits, 14*6 per cent, and 12*7 per cent. ; only one 

 variety, the Auschaer hops, yielding notably lower figures, 9*8o-7'O4 

 per cent. On comparing these figures with the percentage of soft 



1 Zeitschrift /. d. ges. Brauwesen, 1898, 407. 



2 Zeitschrift f. d. ges, Brauwesen, 1898, 409. 



