If you’ve ever smelled a Muscat or Gewürztraminer wine, you probably noticed that it smelled like flowers. Where does this smell come from? Terpenes.
What are terpenes?
Terpenes are found in the skin of the grape. They constitute many of the floral, citrusy, or spicy compounds in essential oils. They are also responsible for the floral smell of marijuana.
Terpenes are made up of hydrogen and carbon, and they can produce different smells depending on the arrangement and length of those molecules. Sometimes you will see them called monoterpenes (containing 10 carbons), sesquiterpenes (containing 15 carbons), or diterpenes (containing 20 carbons).
The most common terpenes in wine, including linalool, geraniol, and nerol, are monoterpenes. You’ll find these aromas in Muscat, for example. Rotundone, responsible for the pepper aroma in Syrah, is a sesquiterpene.
Wines described as “aromatic” have a high level of monoterpenes
The Muscat family of grapes (i.e. Muscat Blanc, Muscat of Alexandria, Muscat Ottonel, and over 200 other varieties) is among the most aromatic. Grapes like Riesling or Viognier are somewhere in the middle, and non-aromatic wines like Chardonnay or Pinot Gris have almost no monoterpene aromas.
Muscat, Moscato, Muscadelle…what’s the difference!?
If you like aromatic wines, you’ll like Muscat. Stick to the names on the left!
Terpenes get “revealed” during fermentation
Terpenes develop in the vineyard but their aromas become volatile during fermentation. It’s been shown that the more mature the grape when it is picked, the greater the terpene content in grape skins. And since terpenes are located in the skin of the grape, terpene aromas in wine can be enhanced by skin maceration (soaking the juice/wine with the grape skins).
Before fermentation, terpenes generally exist in their precursor stage when they are bound to a sugar molecule. We cannot smell terpenes in this bound form.“Free” terpenes do exist in grapes but in very small quantities — bound terpenes are 2–8x more common. This means that most terpenes need to be released from those sugar molecules to become odorous.
The aroma gets volatilized (released) via an enzyme that comes from yeast during fermentation, from acid enzymes during aging, or even by bacterial enzymes in your mouth as you are drinking the wine! For more info on how this works, see my aroma precursors blog.
- Terpenes give off floral, citrusy, or spicy aromas in wine.
- Terpenes are made up of carbon and hydrogen. Monoterpenes, the most common type, are made up of 10 carbons.
- Since terpenes are located in the skin of the grape, terpene expression in wines can be enhanced by skin maceration.
- If a wine is called “aromatic” it means it has a high level of monoterpenes.
- Monoterpenes are most present in Muscat grapes, somewhat present in grapes like Riesling, and pretty much non-existent in neutral grapes like Chardonnay.
- Terpenes exist as precursors bound to a sugar molecule. They are volatilized (released) during fermentation thanks to yeast enzymes.