3-Methylindole
Also written skatole, scatole
Quick answer
The faecal, pig-manure smell found in badly processed white pepper — not a compound of the pepper berry but a product of the retting step in which the skin is rotted off.
What it does
Smelled at a gas chromatograph’s sniffing port, 3-methylindole is faecal and reminiscent of swine manure. In a white pepper powder with an intense faecal, cowshed-like off-flavour it shared the highest flavour dilution factors with 4-methylphenol among 22 odour-active compounds, and on the basis of odour activity values these two, with 3-methylphenol and butanoic acid, were proposed as the main sources of the defect.
How it behaves when cooked
Four properties of the molecule, and what they mean at the stove.
- Volatility
- moderate
- Fat solubility
- high
- Water solubility
- low
- Heat stability
- moderate
A fault made before the pepper reaches a kitchen. Samples taken from a retting batch at a Thai production plant showed 3-methylindole forming biochemically during the soak, and white pepper made by a short fermentation under water with frequent water changes contained no substantial amounts of it. In ground white pepper the concentration barely changed over seven months of storage while the faecal note grew stronger, which the authors attribute to the loss of very volatile compounds such as α-pinene that had been masking it: old ground white pepper smells worse without containing more of the off-odorant.
Spices that carry it
Recorded on the compound rather than on each spice, so the two cannot disagree.
An off-odorant reported as formed during retting, on measurements of pepper taken from one retting batch at a Thai plant and read here in the abstract only. It was measured at similar concentrations in most of 50 commercial samples even though the strength of the off-note differed between them.
Not to be confused with
Compounds a reader is likely to take for this one, and why they differ.
4-Methylphenol
The other half of white pepper’s faecal fault, formed in the same retting step: horse-like where 3-methylindole is swine-manure-like.
Questions this page answers
- why does white pepper smell like a farmyard
- what is 3-methylindole in white pepper