Procurement teams are often asked to qualify an essential oil supplier without being chemists. The technical depth belongs to the formulator and the quality department, but the questions that expose a weak supplier are not technical at all. They are questions about specificity, evidence and behaviour: does the supplier answer precisely, in writing, with documents that can be checked? What follows is a question set organised by topic, with a note on what a good answer looks like and what should make you hesitate. Use it for a first evaluation or as the checklist for an annual review.
Which plant, which part, which chemotype: the identity questions
Ask the supplier to state, for each oil, the Latin binomial, the plant part distilled and, where the species has more than one chemical form, the chemotype. Ask for the INCI name used for cosmetic labelling as well. The terminology in this area is defined in ISO 9235, which gives the vocabulary for aromatic natural raw materials, so a supplier who works to it will not be surprised by the question.
A good answer is a short written line: genus and species, plant part, chemotype if relevant, and the INCI name. A weak answer is a trade name ("our rosemary") or a generic description. Two species can share a common name and smell similar while behaving differently in a formula, and a missing chemotype means you cannot know whether the next batch will match the first. If the supplier cannot tell you what they sell, there is little point asking anything else.
Where it grew and who handled it: origin and traceability
Ask where the plant material was grown or collected, whether it was cultivated or wild-collected, in which season it was harvested, and where it was distilled. Then ask the question that separates a story from a system: if you give them a lot number, can they show you the harvest and distillation records behind it?
Good answers describe a defined area and a production network, not only a country. A country alone is rarely precise enough, and a supplier who does their own distillation or works with known distillers can usually say who did what. Ask also how they handle a shortfall: does the next lot come from the same source, or is another source substituted, and would you be told? Our own oils come from an Anatolian production network we know directly, and we can trace a lot back to its harvest origin; that is the level of detail you should expect to be offered, not merely promised.
What was measured and how it is shown: the analysis questions
Ask which tests are run on every batch, which are periodic, and which laboratory performs them. For essential oils the usual set is appearance and odour, relative density, refractive index and optical rotation, plus a GC-MS profile of constituents. Standard methods exist for the physical constants (ISO 279, ISO 280 and ISO 592), and ISO 11024-1 gives general guidance on preparing gas chromatographic profiles, so ask whether the supplier's results follow recognised methods.
A strong supplier supplies a batch-specific Certificate of Analysis with the lot number, actual results, test dates and the method or method reference, and can show several consecutive lots of the same oil. Check that results sit inside the agreed specification and that they vary realistically from lot to lot. Certificates that are identical across lots, or that merely restate the specification, are a warning. If you plan to buy high-value oils, ask what additional authenticity checks are available, since a single GC-MS cannot prove that an oil is unadulterated on its own.
