Image Source

Have you ever wondered how, exactly, essential oils emerge from their source substances?

How, for example, are roses made to yield rose oil? How does calendula transform from a golden flower to a liquid known for its antibacterial, anti-inflammatory, anti-anxiety properties?

If you’re looking to extract a plant’s oils, you’ll encounter numerous options: water, steam and water, and steam distillation; percolation; expression; ecuelle a piquer (pricking a fruit rind to express essence); enfleurage (cold-fat extraction); and most recently, CO₂ extraction. Oils for aromatherapy and holistic therapies have most frequently been derived from their sources via steam distillation or chemical extraction (using hexane, heptane, or ethanol).

Steam distillation has, for many years, stood out as the gold standard for oil extraction, since chemical extraction can leave trace amounts of chemicals in the resulting essential oil—additions that are, as an attorney friend of mine says, “non-optimal.” The most recently employed extraction method, CO₂ extraction, has gained popularity because it offers certain possible advantages over other options.

What Is CO₂ Extraction, Anyway?

Glad you asked! CO₂ extraction, officially known as the “supercritical CO₂ extraction method,” takes advantage of carbon dioxide’s chemical properties. Gaseous CO₂ is pressurized until it transforms into its liquid state, at which point it becomes a solvent that dissolves the source substance’s components to yield the CO₂-extracted oil. Once the source material is dissolved, the CO₂ is depressurized so it can return to its gaseous state and evaporate out of the oil solution. Boom! The result is a CO₂-extracted oil. No heat is involved, as with steam distillation—just atmospheric pressure. We think that’s neato.

Two Kinds of CO₂ Extraction

Within the basic framework of CO₂ extraction are two methods. One, which produces an oil called a CO₂ Select, uses lower pressure to liquefy the CO₂. The resulting oil contains only the source material’s volatile (aromatic) compounds. Some aromatic molecules are too heavy to be derived via steam, so the CO₂ Select oils may smell more intensely akin to the source material than oil derived via steam, because more of the compounds are present in CO₂-extracted oils.

The other CO₂-extraction method uses higher pressure to liquefy the CO₂ for extraction. The resulting oil contains not only the aromatics of the source plant but also the waxes, lipids (fatty acids), and other soluble particles available. The high-pressure process therefore yields a thicker oil, called a CO₂ Total.

The Advantages of CO₂ Extraction

CO₂ oil extraction stands out for a few reasons, all of which boil down to the fact that it can produce a superior product.

• It makes super-clean oils. Like steam distillation, CO₂ extraction yields a truly pure oil, with no funky (read: potentially toxic) additives.
• It keeps oils fresh. Unlike oils derived via steam distillation, CO₂-derived oils have not faced exposure to high temperatures during extraction. Thus, they’re unaltered and not degraded. Steam distillation, because of the high heat required, actually changes the molecular structure of certain compounds in essential oils. That means that the essential oil contains certain substances that didn’t exist in the parent plant. Such changes aren’t necessarily inherently harmful or even always significant, but sometimes preserving the chemical makeup of the plant itself is crucial to a particular treatment goal. CO₂ enables the distiller to preserve the source plant’s molecular structure while concentrating the material’s essential qualities.
• It’s consistent. CO₂ extraction can better ensure the resulting oil’s consistent potency, batch after batch. Steam distillation, on the other hand, can produce oils of varying quality because of batch-specific differences in temperature, pressure, and time.
• It pulls more plant compounds into the oil. Oils extracted from plants using the CO₂ method contain more of the parent plant’s component substances than do essential oils derived via steam or chemical distillation. That grants you access to more of the good stuff—a broader spectrum of the plant’s source particles. CO₂-derived oils, whether totals or selects, hew closer to the chemical makeup of the momma or daddy plant. The aromas of CO₂-extracted oils are more intense, as well.

Personal Preference Matters, Too

Advantages aside, it’s worth noting that CO₂ extraction doesn’t always yield an inherently superior oil. Your preference may take the lead when it comes to choosing between a steam-distilled essential oil and a CO₂ oil, since some oils extracted via the CO₂ process are quite different in aroma profile from their steam-distilled counterparts. For example, patchouli oil extracted via steam smells woody and earthy, while CO₂ patchouli oil smells more “green.”

Bottom line: CO₂ extraction yields a potent, consistent product for aromatherapy and holistic treatment. You may want to compare and contrast the same oils extracted via different methods, to learn what works best for you. Happy scenting!