Know the Difference: Essential Oil VS CO2 Extract VS Absolute VS Hydrosol

Wednesday, October 16, 2019

Know the Difference: Essential Oil VS CO2 Extract VS Absolute VS Hydrosol

If you have just started your aromatherapy journey, then most probably you are only familiar with essential oils. However, did you know that there are other aromatic plant extracts besides essential oils? I’m talking about Absolutes, CO2 Extracts and Hydrosols. These plant extracts also have benefits akin to essential oils and might have their own distinct characteristics not found on essential oils.

Let’s get to know in details the differences between essential oil, CO2 extract, absolute and hydrosol.

ESSENTIAL OIL

Essential oils refer to highly concentrated volatile oils that are extracted from plant materials (e.g. flowers, leaves, fruits, etc.) either by steam distillation or mechanical expression. “Volatile” means that the essential oil will easily evaporate at room temperature when exposed to air for a long time. Each essential oil has its own unique chemical constituents which contribute to its therapeutic properties. Compared to absolutes and CO2 extracts, essential oils contain smaller and lighter molecules, that’s why they can be absorbed more quickly into the body.

There are two methods to extract essential oils: steam distillation and mechanical expression.

Mechanical Expression

Mechanical expression is often used to extract essential oils from the rinds (peels) of citrus fruits. In this method, the citrus fruits are subjected to high mechanical pressure (e.g. piercing the fruit peels) in order to extract the essential oils. Because there is no heat involved during extraction, mechanical expression is also often called as “cold pressed” method.

Essential oils produced via mechanical expression have more intense scent than the distilled versions. However, citrus-based essential oils extracted using this method usually also contain furanocoumarins – a non-volatile chemical compound responsible for causing phototoxicity in citrus essential oils (e.g. lemon, bergamot, etc.).

Steam Distillation

Steam distillation is the most common method of extracting essential oils from plant materials. The practice of steam distillation dates back thousands of years in order to make aromatic waters used in ancient perfumery. The process involves using low pressure steam to extract essential oil from plants. Compared to other plant extraction methods (e.g. solvent extraction), steam distillation has lower production cost, easier process and doesn’t use any chemical solvents.

If you are a fan of citrus essential oils, then it’s highly recommended that you choose the steam distilled version over the cold pressed since it doesn’t contain the phototoxic compound furanocoumarins.

HYDROSOL

There are two products produced during the steam distillation process: essential oil and hydrosol. Hydrosols, also known as hydrolats or flower waters, contain aromatic compounds from plant materials that are water soluble. Compared to essential oils, hydrosols have subtle fragrance and more gentle to the skin. In fact, unlike essential oils which can cause skin sensitization when applied pure on the skin, hydrosols can be sprayed directly on the skin without the need for dilution.

In cosmetic formulation, hydrosols are ideal to be used when formulating facial toners since they’re already water soluble so you don’t need to use a solubilizer, plus they’re very gentle to the facial skin. Hydrosols are also perfect for linen spray because they can add a subtle hint of fragrance without staining your linens (which can be a problem for some essential oils). Take note also that since hydrosols are water-based, they basically have shorter shelf life than essential oils.

ABSOLUTE

There are some aromatic compounds that cannot be extracted via steam distillation (e.g. plant materials that are heat-sensitive). In this case, a solvent is used to extract the aromatic compounds from the plant materials. For absolutes, the solvent used is called hexane – a colorless liquid that is derived from petroleum. The process involves soaking the botanicals in hexane to extract the fragrant molecules which are later separated from the solvent to produce the absolutes.

Compared to essential oils, absolutes have more intense fragrance, thanks to their high concentration of heavier, non-volatile (non-evaporating) aromatic molecules which also contribute to their thicker consistency. Due to their long lasting scent, absolutes are also more preferred ingredients in making perfumes.

Despite their popularity in perfumery, there are some people who don’t like to use absolutes since there could be traces (very tiny amount) of hexane remain in the plant extracts. Absolutes are also more expensive than essential oils.

CO2 EXTRACT

Another type of aromatic plant extracts that are obtained by solvent extraction is the CO2 extracts. Unlike absolutes that use hexane as solvent, CO2 extracts use carbon dioxide. You might ask, CO2 is a gas, so how could it possibly be used as a solvent? With a specific pressure and temperature, the carbon dioxide can be transformed into a “supercritical” state – which is the fluid (liquid) state of CO2. The liquid carbon dioxide is then used to extract the aromatic compounds from the plant materials. After the extraction process, the liquid CO2 is brought back to its gaseous state, so what remains is the CO2 extracts.

Carbon dioxide extraction is the most expensive plant extraction method but it produces the highest quality of aromatic extracts compared to steam distillation. Unlike absolutes, there are no traces of CO2 remain after the extraction process so CO2 extracts are completely safe and natural. CO2 extracts also have longer shelf life than essential oils and absolutes.

The chemical constituents of CO2 extracts are also quite different from essential oils as they also contain heavier aromatic molecules that cannot be extracted by steam distillation. For example, ginger CO2 extract contains the molecules gingerol – a chemical compound found in fresh ginger, which is not present in ginger essential oil. CO2 extracts are said to have closer chemical composition of the original plant.

There are two types of CO2 extracts: CO2 Select and CO2 Total.

CO2 Selects use lower pressure to extract volatile CO2 soluble aromatic compounds. Consistency wise, CO2 selects are quite similar to essential oils. On the other hand, CO2 Totals are extracted using higher pressure and contain both volatile and non-volatile CO2 soluble aromatic compounds. Moreover, CO2 totals have thicker consistency since they also contain heavier molecules like waxes and resins.

References:

A Beginner’s Guide to Essential Oils Part 1: Essential Oil Extraction. Retrieved from https://tisserandinstitute.org/beginners-guide-essential-oils-part-1-essential-oil-extraction/

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