Compounds · Ketones · Microbial origin
Diacetyl
Also known as 2,3-Butanedione · Biacetyl — an analysis may use any of these names
Butter, cream, fatty sweetness. At high concentration it turns into an unpleasant artificial-butter note.
- CAS
- 431-03-8
- Formula
- C4H6O2
- Molar mass
- 86.09
- Odour threshold
- 10 ppbin water
- Boiling point
- ≈ 88 °C at atmospheric pressure
This compound boils at 88 °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 58 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.
About the threshold figure
Moderately low. It gives a buttery note at low concentration and a harsh one at high concentration.
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 four-carbon diketone, a very small molecule boiling at 88 degrees. It evaporates almost instantly, but its extremely low detection threshold makes up for that.
Where else you meet it
Butter, fermented milk, fermented bean curd, beer, and industrial butter-flavoured popcorn.
Dictionary entries that mention this compound
Regulatory note
Subject to occupational exposure limits in the food industry in some countries. This is a labelling requirement, not a warning about the product.