Compounds · Other compounds · Microbial origin
Acetic acid
Also known as Ethanoic acid · Acid axetic — an analysis may use any of these names
Vinegar, sharply sour, stinging the nose. No layer behind it.
- CAS
- 64-19-7
- Formula
- C2H4O2
- Molar mass
- 60.05
- Odour threshold
- 20.0 ppmin water
- Boiling point
- ≈ 118 °C at atmospheric pressure
This compound boils at 118 °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 93 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
Very high — measured in parts per million, not parts per billion. It takes a large amount to be smelled, which is why vinegar has to be strong to have a smell.
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 two-carbon acid whose carboxyl group forms double hydrogen bonds, so it boils much higher than its tiny size would suggest.
Where else you meet it
Pickles, vinegar, spoiled wine, and the late stage of every lactic fermentation.