Lesson 1 of 2 in this stage
From liquid to nose: volatility and detection thresholds
Explain why the most abundant bottle ingredient is not necessarily the strongest impression.
We smell what reaches us through air
For a material to be smelled, molecules must reach the nose in air and evoke an olfactory response. Bottle liquid is not identical to the air mixture above it: some materials enter that air more readily than others. This region is often called headspace. A material's liquid fraction is therefore not directly its fraction at the nose.
Volatility and detection threshold are different factors
Volatility concerns a material's tendency to enter the vapour phase under given conditions. A detection threshold is the lowest level detectable in a defined test, varying by material, person and method. A small airborne amount may be noticeable if its threshold is low, while a more abundant material is less prominent. Ingredient amount alone cannot rank perceived notes.
The opening is not simply the lightest molecule
Over time, release changes along with mixture balance and sensory adaptation. A later impression may emerge because a competing one subsides, not because it only then begins evaporating. Molecular weight may relate to some properties but cannot alone rank volatility or perceived strength in a complex formulation. Materials, the medium and perception all matter.
A numerical illustration, not a perfume recipe
Imagine a teaching example: airborne A is 10 units with a detection threshold of 1; B is also 10 units but has a threshold of 20. Equal amounts place A above its threshold and B below its threshold in this example. Real mixture perception still cannot be fully predicted by this ratio because perceptual interactions matter.
Material abundance is not the same as odour prominence
Molecules reaching the air depend partly on volatility and their behaviour within a mixture and on a surface. Once airborne, human odour-detection thresholds matter: some molecules are detectable at very low concentrations while others require more. The material occupying the greatest proportion of a bottle is not necessarily its most recognizable scent.
Why note pyramids are not precise scientific clocks
Evaporation, air transport, interactions within the blend and human perception overlap. An impression may recede while another grows noticeable because masking changed. “Top, heart and base” can be useful teaching language without implying rigid molecular hand-offs or universally fixed minute marks.
Your turn
Use what you learned
Why cannot ingredient percentages alone reveal the order of perceived notes?
See the answer and why
Liquid fractions differ from headspace, detection thresholds vary, and mixture interactions and adaptation affect perception over time.
Check your understanding
Answer four questions, then review the reason for each answer. You can retry.
Interpret the evidence
Volatility alone cannot predict perception. Vapour pressure, partitioning, detection threshold and adaptation all contribute; a low-dose odorant may dominate a higher-concentration material.
SESH exercise: choose two scents and record results before viewing their marketing descriptions.
