Alpha Acids
The main bittering compounds found in the lupulin glands of hop flowers. There are actually many different alpha acids, the main ones being humulone, cohumulone and adhumulone. Alpha acids are not very soluble at cold temperatures and must be isomerised before they can dissolve into beer.
Closely related: Alpha Acid Units
Brugse Zot blond from Brewery De Halve Maan is available in the Beer Store