Compounds · Phenols · Heat (Maillard reaction and pyrolysis)
Guaiacol
Also known as 2-Methoxyphenol — an analysis may use any of these names
Smoke, tobacco, asphalt. This is the molecule of a fire that has gone out.
- CAS
- 90-05-1
- Formula
- C7H8O2
- Molar mass
- 124.14
- Odour threshold
- 3 ppbin water
- Boiling point
- ≈ 205 °C at atmospheric pressure
For this compound the two axes sit close together. Volatility tells you whether it leaves a surface early or late; the threshold tells you how much of it the nose needs before it notices.
Where it comes from
Biosynthetic pathway: Heat (Maillard reaction and pyrolysis) — fire breaks large molecules into ones you can smell.
Guaiacol is classed under heat because in everyday life it forms when fire breaks down lignin. But lignin itself is a phenylpropanoid polymer made by the plant. Heat does not create new atoms — it only breaks large molecules into small ones light enough to reach your nose.
About the threshold figure
Low. A small amount is enough for a clear smoky note, which is why smoked food is recognised at once.
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 phenol with a methoxy group, forming good hydrogen bonds, so it boils at around 205 degrees and stays noticeably on surfaces.
Where else you meet it
Wood smoke, smoked meats, whisky aged in charred barrels, and some dark-roasted coffees.