There are four layers of fraud in the essential-oil trade, ordered by how hard they are to detect. This lesson covers the first: dilution with something that is not essential oil.
It is the crudest layer, and also the most common, because it is cheap and easy.
Four common fillers
Carrier oils. Fractionated coconut oil, almond oil, jojoba oil. They are colourless, have no significant smell, and are tens to hundreds of times cheaper than essential oil.
Alcohol. The cheapest, and it evaporates, so after a few minutes it is hard to detect by nose.
Mineral oil. A petroleum product, odourless, and the worst filler because it has no plant origin at all.
Phthalates and other plasticisers. Less common but they do exist, mainly in goods of unknown origin.
Traces on paper
The simplest test needs a sheet of plain uncoated white paper and four hours.
Put a drop on the paper. Wait. Real essential oil will evaporate and leave a very faint mark or none at all — except for some especially heavy oils such as vetiver or resins, which may leave a light mark.
If after four hours you see a round, shiny oil stain that does not evaporate, there is a non-volatile substance in the bottle.
But don’t jump to the conclusion that it is carrier oil. There is a very common group of products in Vietnam that gives a false positive: cold-pressed citrus peel oils. Because they are not distilled, they carry the waxes and pigments of the peel — non-volatile substances — so they leave an oil stain just like a blended sample.
With cold-pressed lime, orange, pomelo or mandarin, the paper test tells you nothing. The same goes for absolutes and resinoids, which are also thick and also leave a mark.
The test is not perfect — it does not detect alcohol, and it gives false results with a few thick oils. But it is free and catches the most common layer of fraud.
Traces on an analysis
On a GC/MS analysis, dilution leaves two signs.
The total of the characteristic components drops unusually. If a lavender sample has only forty per cent of lavender’s characteristic components while the normal range is eighty to ninety, the other sixty per cent is something else.
Peaks appear that do not belong to the species. Carrier oils contain fatty acids and triglycerides. They are heavy and usually do not evaporate under ordinary analysis conditions, but when present in large proportions they still leave a trace.
Limits of the test
Alcohol evaporates before you can do the paper test, and it does not show clearly on an ordinary GC/MS either because it comes off too early.
With alcohol, the practical test is smelling: a sample diluted with alcohol has a sharp, cold beat in the first three seconds, like rubbing alcohol, then suddenly weakens. Real essential oil has no such drop.
The next lesson covers the second layer, one step harder: filling with a cheaper essential oil from the same group.