The Brewer

Terpenes Explained: The Chemistry of Aroma

Terpenes: The DNA of Hop Flavor

When you smell a hop and say “that smells like mango,” you aren’t smelling a mango. You are smelling a specific chemical compound called a Terpene.

Terpenes are volatile aromatic oils found in plants (pine trees, cannabis, lemons, and hops). Understanding them allows you to be a better brewer. Instead of blindly following hop descriptions, you can look at the chemical analysis and know exactly what that hop will do.

The Big Four

There are dozens of terpenes in hops, but these four dominate the profile.

1. Myrcene (The Green One)

  • Aroma: Herbal, woody, grassy, green, resinous.
  • Found In: Cascade, Chinook, Simcoe (often 40-60% of total oil).
  • Boiling Point: Very low (147°F / 64°C).
  • Brewing Tip: Because it boils off so easily, Myrcene is lost in the boil. If you want this flavor, you must Dry Hop or Whirlpool at low temps.

2. Humulene (The Spicy One)

  • Aroma: Earthy, woody, spicy (like black pepper).
  • Found In: Noble hops (Hallertau, Saaz), Goldings.
  • Character: This is the signature smell of European Lagers and English Ales. It is elegant and refined, not shouty.

3. Caryophyllene (The Woody One)

  • Aroma: Cedar, woody, spicy, clove.
  • Found In: Goldings, Northern Brewer.
  • Science: Often found alongside Humulene. It is prone to oxidation, which can turn it into a “stale” aroma.

4. Linalool (The Floral/Fruity One)

  • Aroma: Lavender, orange blossom, Fruit Loops.
  • Found In: Citra, Mosaic, Amarillo, Centennial.
  • Importance: Even though it makes up a small % of the oil, our noses are extremely sensitive to it. It is often considered the “indicator” terpene for a good modern IPA.

Biotransformation

This is where it gets crazy. Yeast can chemically change terpenes.

  • Geraniol (smells like roses) can be transformed by yeast into Beta-Citronellol (smells like lime/citrus).
  • This is why adding hops during fermentation (active dry hopping) creates different flavors than adding them after.

How to Use This Knowledge

Next time you buy hops, look at the Oil Analysis on the package.

  • Want a dank, resinous West Coast IPA? Look for high Myrcene and Pinene.
  • Want a floral, delicate Saison? Look for high Linalool and low Myrcene.
  • Want a spicy Pilsner? Look for Humulene.

You are no longer guessing. You are engineering flavor.