There is no single thymol figure that all good ajwain meets. Ajwain seed usually contains a few percent volatile oil, and thymol is normally the main component of that oil. Both figures vary with variety, growing area, season, harvest, drying and age.
So the useful question is what your product needs. Set a minimum for volatile oil, and if aroma strength is critical, a minimum thymol share in the oil, then test each lot.
Two numbers, not one
Thymol can be reported in two different ways, and mixing them up causes disputes.
- Volatile oil content: how much essential oil the seed yields, as a percentage of seed weight. For illustration, figures of roughly 2 to 4 percent are often seen in good ajwain, but lots outside that range are traded.
- Thymol in the oil: what share of that oil is thymol, as a percentage of the oil. For illustration, figures from around a third to over half are often reported.
- Thymol in the seed: the two multiplied together, which is far lower than either figure suggests.
Always state which one you mean, and the test method, in your specification. A supplier quoting thymol in the oil and a lab reporting thymol in the seed can both be right and still disagree by a large factor.
What affects thymol
- Variety and growing region.
- Weather during the crop, including heat and rain.
- Harvest timing and maturity of the seed.
- Drying and handling, since overheating loses oil.
- Storage time and conditions, because volatile oil fades with age.
- Cleaning grade, as dust and stalks dilute oil content.
Setting a limit for your use
For culinary whole seed, a reasonable volatile oil minimum is usually enough. Your sensory panel will tell you if aroma is right. For grinding into blends, oil content matters more, because powder loses aroma faster. For essential oil distillers, oil yield and thymol share are the main measures of value.
Ask suppliers for lab results on their recent lots, then set your minimum from your own trials rather than from a leaflet. The general guide on writing an agri product specification shows how to add a test method and tolerance.
How it is tested
Volatile oil is usually measured by steam distillation of a ground sample. Thymol share in the oil is usually measured by gas chromatography. Use an accredited lab, and use the same lab for the approval sample and the shipment so the results compare. Our guide on reading a lab certificate covers what to look for on the report.
How we help
We have ajwain samples from several processors tested for volatile oil and thymol at an NABL-accredited lab, so you can set a realistic minimum. We then check the shipment against it. Ask for a free sourcing review.