May 25, 1914 
Aroma of Hops 
139 
CHEMICAL PROPERTIES OF THE FRACTIONS 
ACID, ESTER, AND SAPONIFICATION NUMBERS 
. The chemical properties of the oils and fractions are much more 
important in determining constant differences or similarities in the vola¬ 
tile oil of hops than the physical properties previously discussed. This 
is especially true of the aromatic quality of the oil, since quality is depend¬ 
ent upon the ester content. The ester content is expressed in the form 
f20 
3 
RRACT/OMS 
Fig. 8.—Optical-rotation curves of hop oils from the crops of 1908. 
of ester numbers based on the amount of esters in i gram of the oil. The 
acid numbers of the fractions are less important, since these depend 
largely upon the extent of decomposition which the esters undergo during 
fractionation. Only a small amount of decomposition of the esters is 
required to liberate sufficient acid to produce high acid numbers, since, 
as has been shown, the acids in combination with the esters are those of 
high molecular weight. Owing to the consequent irregularity of the 
