CO2 Extracts of Resins: Frankincense, Myrrh and Benzoin

CO2 extracts of resins are materials obtained by dissolving frankincense, myrrh or benzoin in carbon dioxide held above its critical point (31.1°C and roughly 74 bar), then releasing the pressure so the CO2 flashes back to gas and leaves the aromatic and resinous matter behind. Unlike steam distillation, which only carries over volatile, water-immiscible compounds, CO2 can also pull larger, less volatile molecules such as resin acids and diterpenes, so the result sits closer to the smell of the raw resin than an essential oil does. Because the solvent leaves no residue, producers distinguish a lighter “CO2-select” extract, run at lower pressure and close to the essential oil profile, from a heavier “CO2-total” extract that resembles an absolute or resinoid. Frankincense and myrrh take well to the process; benzoin, for chemical reasons explained below, mostly does not.

What is CO2 extraction, and why use it on resins?

Carbon dioxide becomes a supercritical fluid once it is compressed and warmed past its critical point, meaning it takes on properties of both a gas and a liquid: it diffuses into the resin’s cell structure like a gas but dissolves aromatic and resinous compounds like a liquid solvent. Extraction happens well below the temperatures used in steam distillation, so heat-sensitive constituents survive intact, and because CO2 is non-flammable and non-toxic in the concentrations used, no solvent residue analysis is needed the way it is for hexane-based resinoids.

Pressure controls selectivity. At lower pressure (around 80–100 bar), CO2 behaves more like a light nonpolar solvent and extracts mainly monoterpenes and sesquiterpenes, producing an oil-like fraction often sold as “CO2-select.” Raising pressure toward 300–400 bar increases the density and solvent power of the CO2, pulling in diterpenes, resin acids and waxy material for a “CO2-total” extract that is thicker, darker and more faithful to the smell of the intact resin.

Frankincense CO2 extract: what changes from the raw resin

Frankincense, the dried oleo-gum-resin of Boswellia sacra and related species, is one of the resins best suited to CO2 processing because its aromatic fraction spans both volatile monoterpenes and heavier diterpene compounds that distillation struggles to carry over. A CO2-total extract typically retains more of the diterpene fraction, including incensole acetate, a compound largely absent from steam-distilled frankincense oil because it is too heavy to travel with steam.

What does CO2-extracted frankincense smell like?

Where distilled frankincense oil reads bright, piney and citrus-forward from α-pinene and limonene, a CO2 extract carries that same lemony-piney top note but sits on a noticeably heavier, waxier, more resinous base. The overall effect is closer to breaking open a fresh tear of resin than to the distilled oil sold in aromatherapy shops. Perfumers who want the incense character to read past the top notes, as discussed in Frankincense in Perfumery and in The Incense Note in Modern Perfumery, often reach for the CO2 version specifically for that persistence.

Myrrh CO2 extract: bitterness and smoke without water

Myrrh, from Commiphora myrrha, is harder to distil cleanly because its resin contains a substantial gum fraction and its most characteristic sesquiterpenes are prone to oxidation under steam heat. CO2 extraction avoids that heat exposure and yields a dark, viscous extract rich in furanoeudesma-1,3-diene, curzerene and lindestrene, the compounds responsible for myrrh’s bitter, smoky, medicinal facets. The extract smells less sweet and more animalic-bitter than the resinoid, with a stronger sense of the raw material’s characteristic sharpness, a quality perfumers working in oriental and chypre structures value, as covered in Myrrh in Perfumery.

Why benzoin is rarely a CO2 extract

Benzoin, whether Siam or Sumatra type, behaves differently from frankincense and myrrh because its most valuable odorants are polar, crystalline solids rather than volatile terpenes. Benzoic acid, cinnamic acid, coniferyl benzoate and vanillin are the compounds that give benzoin its sweet, vanilla-balsamic character, and all of them dissolve far more readily in polar solvents like ethanol than in nonpolar CO2. This is why benzoin is almost always processed as a solvent resinoid or a simple tincture rather than a CO2 extract; suppliers who do offer a benzoin CO2 extract usually add ethanol as a co-solvent, which blurs the line between “CO2 extract” and “resinoid” in practice. Comparisons of the extraction methods and their effect on the finished material are discussed in Benzoin Absolute vs Resinoid vs Tincture.

Comparing the three CO2 extracts

Using CO2 resin extracts in a formula

CO2 extracts of frankincense and myrrh are typically dosed as base or heart notes, added later in the maceration than the top-note terpenes they resemble because the extract itself already leans heavier and slower to volatilize than the corresponding essential oil. They fold well into amber accords and incense structures alongside labdanum, and because they carry more of the resin’s non-volatile fraction than a distillate, they also perform better as long-term fixatives in a finished composition. Formulators substituting a CO2 extract for an essential oil in an existing formula should expect to use it at a lower percentage, since its odor intensity per gram is generally higher and its residual waxy content can affect the clarity and pour of an alcohol-based perfume if used above a few percent.

What to check before buying

Because “CO2 extract” is not a legally defined term, quality and even the extraction method vary between suppliers. A genuine CO2-total extract of frankincense or myrrh should be viscous, dark and strongly odored straight from the bottle, closer in weight and color to the raw resin than to a thin essential oil. For benzoin, be skeptical of anything labeled “CO2 extract” that pours and smells identical to a standard resinoid; it is more likely a co-solvent extraction relabeled for marketing. Buyers assembling a small library of resin extracts for comparison may find it useful to read alongside pieces on resinoid production and on resins in perfumery generally, both of which cover the solvent-based alternatives that CO2 extraction sits next to on a supplier’s list.

• co2-extraction
• frankincense
• myrrh
• benzoin
• perfumery