What Are Sesquiterpenes and Their Role in Oud Scent?

If the scent of oud is a blend of aromatic families, the sesquiterpenes are among the most prominent of these families and the most linked to oud's depth and its woody character. In this article we simplify what these compounds are, and why much of oud's warm notes are attributed to them, with honesty in distinguishing what is known from what is still under research.

What are sesquiterpenes?

Sesquiterpenes are a wide family of natural aromatic compounds produced by many plants, among them the oud tree. They are relatively medium-sized molecules, heavier than the light, fast-evaporating compounds, and so they are usually linked to the depth of the scent and its persistence more than to the fleeting top notes. Their scientific name refers to their chemical structure, but what matters to us here is their role in the scent, not their laboratory details.

This family is considered among the most distinctive of oud wood, since its types vary within a single piece, so it combines what gives the dry woody character, what tends toward the earthy, and what adds a balsamic warmth. This internal variety is a main reason for the richness of oud's scent compared with simpler aromatic woods.

What do they add to oud's scent?

Much of the qualities by which we describe the "heart" of oud's scent are attributed to sesquiterpenes:

• The woody character: the deep, dry note we associate with authentic oud.
• The earthy touch: a depth reminiscent of damp earth or roots in some types.
• Warmth and persistence: the scent lasting longer because these molecules are slower to vaporize than the light ones.

But we note honestly: this is a general attribution to a family, not an equation for a single molecule. Within the sesquiterpenes are many types, each with its own character, and the final scent is the outcome of their interaction with the chromones and the rest of the compounds, not the product of this family alone.

What does this mean for you practically?

You do not need to know the names of the molecules to enjoy oud, but understanding the role of this family gives you more precise vocabulary to describe what you smell: when you smell a warm woody depth that lasts after the first note calms, you are usually in the presence of sesquiterpenes. This understanding helps you later in the article on "writing a professional description of the scent."

And in the following article we move to the second family distinctive of oud wood: the chromones, and how they complete the picture of the scent that the sesquiterpenes began.