Bitterness and Aroma

Hops provide two different elements: bitterness from phenolic “alpha acids” in their resins, and aroma from their essential oil. Some hop varieties contribute a dependable level of bitterness, while others are prized for their aroma.The important bittering compounds are the alpha acids humulone and lupulone. In their native form they’re not very soluble in water, but prolonged boiling transforms them into soluble structures that flavor the beer effectively. (Brewers sometimes use hop extracts that have been pretreated to produce the more soluble alpha acids.) Because boiling evaporates away many of the volatile aroma compounds, another dose of hops is sometimes added to the brew after the boiling, specifically to add aroma. The aroma of ordinary hops is characterized by the terpene myrcene, which is also found in bay leaf and verbena, and is woody and resinous. “Noble” hop varieties are dominated by humulene, which is more delicate, and often contain pine and citrus notes from other terpenes (pinene, limonene, citral). The American variety “Cascades” has a distinctive floweriness (due to linalool and geraniol).