The scent note system, top, middle, and base, is a fragrance industry framework that maps directly onto terpene chemistry. Top notes are the most volatile compounds: they evaporate quickly, hit the nose immediately, and fade within 20 to 30 minutes. Middle notes (or heart notes) emerge after the top notes dissipate and define the core aromatic character. Base notes are the heaviest and least volatile compounds; they linger for hours and provide the foundation that gives a fragrance staying power and complexity. Understanding this framework through the lens of terpene molecular weight makes the system mechanistically intuitive.
Terpene volatility and note assignment
Monoterpenes (C10) are overwhelmingly top notes: they're the first thing you smell because they evaporate fastest. Limonene, alpha-pinene, and linalool all lead this category. Sesquiterpenes (C15) generally function as middle to base notes depending on their specific structure. Beta-caryophyllene, humulene, and bisabolol are effective base and heart note contributors: they're substantive enough to persist while being aromatic enough to contribute character. In terpene blend formulation, this means balancing your monoterpene-to-sesquiterpene ratio based on how long you want the aromatic experience to last.
Top notes (monoterpenes) give a fragrance its first impression but fade fastest. Base notes (sesquiterpenes and larger) carry the blend for hours. A perfume that smells only of citrus and disappears in 30 minutes has no base. A blend that smells earthy and flat immediately has no top. The art of aromatic blending is balancing across all three note tiers.
Building a balanced blend
A functional aromatic blend works because each note tier serves a distinct purpose and the tiers interact over time. Top notes handle the first impression: they're the reason someone finds a scent immediately appealing or dismisses it. Middle notes are the aromatic core: what the blend is about after the top notes dissipate. Base notes create temporal continuity, making wear or diffusion feel like a coherent experience rather than a series of disconnected aromatic flashes. When formulating with terpene isolates, the implication is direct: a monoterpene-heavy blend with no sesquiterpene foundation will smell bright for 30 minutes and then disappear. A sesquiterpene-forward blend with no monoterpene top layer will smell flat on first impression and never earn a second encounter. Balancing across all three tiers is not aesthetic preference; it is the functional requirement that makes any aromatic blend work at all. The specific ratios depend on application, concentration, and target aromatic character.
The perfumery blending formulas, top/heart/base ratios by aromatic style, isolate-by-application reference tables, and carrier-oil concentration guides, are in Chapter 11 of the printed book.