Almost every problem with buying frankincense comes from the same place: the word does too much work. It names a genus of roughly twenty trees, a hard aromatic resin, a distilled oil, a solvent extract, and a five thousand year old idea about the sacred. Those are five different things and only two of them come in a bottle.
Which frankincense?
The trees are Boswellia, in the Burseraceae, the same family as myrrh and elemi. Four species dominate the trade and they are not interchangeable:
- B. sacra (Oman) and B. carterii (Somalia) are the classic Arabian and Horn of Africa frankincense, and effectively the same material to most noses.
- B. papyrifera (Ethiopia and Sudan) is the volume species behind a great deal of church incense.
- B. frereana (Somalia) is the one that carries no water-soluble gum at all, which is why it burns cleanly.
- B. serrata (India) is the subject here, and it is the odd one out.
Serrata grows in the dry deciduous forest of central and western India, through Rajasthan, Gujarat and Madhya Pradesh and up into the Punjab. It is not a stand-in for the Arabian material and it never was. It has its own name, its own tradition and, as it happens, its own chemistry.
In India it is salai or salai guggul, and shallaki in Sanskrit. That is the name it carries in Ayurveda, where the resin has been used for a very long time indeed. The caravan trade that carried frankincense north out of Arabia and Africa is a genuinely famous story, and it is not this tree's story. Serrata stayed home.
What stays behind in the still
This is the important part and it is almost universally muddled.
The compounds frankincense has become famous for in the last twenty years are the boswellic acids, and every piece of research you have seen quoted about them was done on the resin or on a solvent extract of it. Boswellic acids are large, heavy, non-volatile triterpene acids. They cannot be carried over by steam, which means they are not present in any steam-distilled frankincense essential oil, of any species, at all.
None of that makes the oil less interesting. It makes it a different product, and it means that any oil listing leaning on boswellic acid research is describing something it does not contain. If boswellic acids are what you are after, the resin itself or a CO2 extract of it is the honest route, not a distilled oil.
What does come over
What the still carries is the light monoterpene fraction, and here serrata parts company with the rest of the genus. Most Boswellia oils lead on alpha-pinene. B. serrata leads on alpha-thujene, which is unusual, and it is the main reason the oil smells sharper, greener and more lemony than the warm balsamic profile people expect from the word frankincense.
It also varies enormously. Published lot analyses of serrata oil have shown alpha-thujene anywhere from around forty per cent to over seventy, in material from the same supplier. That is not adulteration, it is a natural product doing what natural products do, but it means two honest bottles of serrata can smell noticeably different from one another.
One practical quirk: serrata oil can go cloudy or partly solid at room temperature. Warm the bottle in your hands and it clears. Nothing is wrong with it.
The awkward part: serrata is also an adulterant
Because it is cheaper than Arabian and Somali frankincense and comes from the same genus, serrata gets quietly blended into oils sold as B. carterii. A published authentication study of commercial frankincense oils found exactly that among a long list of other problems: samples cut with synthetic limonene, synthetic octyl acetate, castor oil, and in several cases substituted or partly substituted with serrata.
The cheapest way to fake expensive frankincense is with cheaper frankincense. Which makes serrata sold honestly, under its own name, the more trustworthy purchase of the two.
That is the argument for buying it as itself. A bottle labelled Boswellia serrata, priced like Boswellia serrata, is telling you the truth. A suspiciously affordable bottle labelled carterii may well be the same oil at three times the price.
How to read a frankincense label
Three things, in order. The species, written in full, because "frankincense" alone tells you almost nothing. The part and the method, since resin, distilled oil and CO2 extract are three different products with three different chemistries. And the claims, because anything invoking boswellic acids on a distilled oil is either confused or hoping you are.
Get those three right and serrata is a lovely thing: bright, resinous, dry, more lemon and pine than church, and an excellent bridge between citrus and the heavier resins.