Compounds · Alcohols · Microbial origin
Ethanol
Sharp, clean, cold, flat. No layer behind it.
- CAS
- 64-17-5
- Formula
- C2H6O
- Molar mass
- 46.07
- Odour threshold
- 100.0 ppmin water
- Boiling point
- ≈ 78 °C at atmospheric pressure
This compound boils at 78 °C, so it is lighter than any ordinary essential-oil component. It lies outside the 150–290 °C band, so the marker stops at the left edge — not because that is where it sits, but because the axis does not reach that far.
The two axes are 100 points apart. Volatility tells you whether the compound leaves a surface early or late; the threshold tells you how much of it the nose needs before it notices. When the two sit this far apart, they explain things the percentages on an analysis cannot explain on their own.
Where it comes from
Biosynthetic pathway: Microbial origin — made by bacteria and yeasts, not by plants.
Ethanol, acetic acid and fruity esters are all made by yeasts and bacteria, but the raw material is the plant’s sugar. The microbial pathway is almost always a second layer placed on top of what the plant has made.
About the threshold figure
The highest in this table. Ethanol is almost invisible to the nose until very high concentrations.
Published thresholds differ by several orders of magnitude, because of differences in measuring method, sample purity and panel. The figure here is an order of magnitude for relative comparison, not a measurement. We give it only for compounds where the literature broadly agrees — 52 of the 106 compounds in the library. The rest are left blank rather than guessed.
Why it sits where it does
A molecule of only two carbons, the smallest on this whole list. It boils at 78 degrees and evaporates almost instantly — well outside the usual volatility band of essential oils.
Where else you meet it
Rubbing alcohol, alcoholic drinks, and the base solvent of almost every perfume.