1) Bitter compound 2) Organic acid 
These come from the soft resin of the hop flower. They are made of humulone, ad-humulone and co-humulone.
Alpha acids (α acids) are a class of chemical compounds primarily of importance to the production of beer. They are found in the resin glands of the flowers of the hop plant and are the source of hop bitterness. Alpha acids may be isomerized to form iso-alpha acids by the application of heat in solution. Iso-alpha acids (iso-α-acids) are typical...
the soft, bitter hop resin responsible for most of beer
These come from the soft resin of the hop flower. They are made of humulone, ad-humulone and co-humulone.
A sticky, bitter resin found in hops, which imparts bitterness to the finished beer.
The primary compounds in hops that give beer its bitterness. The amount of alpha acid in hops