Not All Bitterness Is the Same
An IBU is an IBU, right? Not quite. As it turns out, different alpha acids impact flavor uniquely. Using Amarillo hops creates a pleasant grapefruit taste. Brew with Chinook instead and the beer tastes harsh, catty, and raspy. This effect is due to the essential oils as well as the alpha acids.
Humulone — The primary alpha acid found in hops. The bitterness from humulone is smoother and softer.
Cohumulone — In descriptions, direct measurement of cohumulone is sometimes given. Both supported and disproved by blind testing, brewers believe that cohumulone-derived bitterness is harsh and raspy. Newly developed hop varieties are often marketed as “low cohumulone.”
Adhumulone — Found in small amounts in hops. Its impact is unclear.
Some of the low “coho” hops seem to lack the hop “punch” that makes bitterness noticeable. The need to push the bitterness envelope sometimes requires a boost. Adding small amounts of a high-cohumulone hop like Chinook provides that beer-popping backbite.
Hop Aroma and Flavor
Essential oils are volatile hydrocarbons easily vaporized by boiling. Found in small fractions in hops, very little stays in the beer, but those tiny amounts make huge impacts.
Major Flavor Sensations
Citrus — Ranging from lightly orange to massive, face-slapping grapefruit character, they appear in a number of American ales.
Floral, Grassy, Herbal — Associated with the classic British hops, these milder tones can be overshadowed by other potent aromas.
Noble “Spicy” — Hop growers throw the term “noble” around. Technically the term refers to a set of German and Czech hops, Hallertau, Tettnanger, Spalt, and Saaz. The noble hop character is spicy with additional complexity from oxidized oils and beta acids
Piney — Common in American-style beers. While the Europeans heavily use the British/German/American Northern Brewer hop, it is more woody than piney.
Essential Oil Groups
Cadinene, Citral, Limonene, Myrcene — Citrus notes, often found in well-known American hop cultivars such as Cascade or Centennial.
Caryohyllene, Humulene — These provide the spicy herbal charge for many German and European beers. Noble hop cultivars mostly contain humulene. Both oxidize easily, contributing to the “noble” profile.
Nerolidol, Pinene, Terpineol — Woody, piney, and resinous, found in hops like Chinook and Northern Brewer.