56 THE HOP. 



property of the hop leaves when agitated in the copper, 

 and by the formation of a fiher bed for the fihration of 

 the wort in the hop back; (4) to preserve the beer 

 by the antiseptic influence of some of their constitu- 

 ents; (5) to assist in the steriHzation of the wort. 



"The bitter flavor is imparted by some of the resin' 

 and the so-called hop acid (hopfoibittcrsaiirc); th. 

 aroma by the volatile oils; the precipitation of the 

 nitrogenous matters by the tannic acid, and the anti- 

 septic properties by certain of the resins. It is there- 

 fore essential tliat hops, to be of value, should contain 

 these substances in due proportions. 



"The percentage of tannic acid in hops is stated 

 by communications from the Agricultural Laboratory 

 of Vienna to range from 1.38 to 5.13 per cent., the 

 average being between 3 and 3.5 per cent., and this, so 

 far as we know, is the normal amount found in good 

 hops. The percentage of volatile oil, shown by the 

 analyses contained in the report from the Austrian 

 laboratory named above, ranges from 0,15 to 0.48, the 

 average being about 0.25 to 0.35. To these oils wc 

 owe the aroma and delicate flavor of the beer. 



"The bittering principles of hops are still the sul)- 

 ject of considerable divergence of opinion. According 

 to Hayduck, the resins are the essential bittering prin- 

 ciple, and as Hayduck's researches are the most recent 

 and are characterized by completeness and definitcne^s. 

 it is probable that his views are more worthy of err 

 dence than those of the older investigators. Amon' 

 these is Lermer, who claims to have separated a crys 

 talline bitter acid from hops, to which he attribute'; 

 their bittering properties. The acid is insoluble in 

 water, but soluble in dilute alcohol, imparting to the 

 solution an intensely bitter taste. 



"Julich se])aj'ated an intensely bitter substance 

 from hops, which was easily soluble in water. Bun- 

 gener attributes the bitter to a substance partially of an 



