56 THE HOP. 



property of the hop leaves when agitated in the copper, 

 and by the formation of a filter bed for the filtration 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 sterilization of the wort. 



"The bitter flavor is imparted by some of the resins 

 and the so-called hop acid (hopfcnbittcrsaurc)\ the 

 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 that 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 we 

 owe the aroma and delicate flavor of the beer. 



"The bittering principles of hops are still the sub- 

 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 definiteness, 

 it is probable that his views are more worthy of cre- 

 dence than those of the older investigators. Among 

 these is Lermer, who claims to have separated a crys- 

 talline bitter acid from hops, to which he attributes 

 their bittering properties. The acid is insoluble in 

 water, but soluble in dilute alcohol, imparting to the 

 solution an intensely bitter taste. 



"Julich separated an intensely bitter substance 

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

 gener attributes the bitter to a substance partially of an 



