Top 4 Ways to Extract Essential Oils from Plants

Essential oils are hydrophobic, hydrocarbon liquids extracted from plant material that are valued for their aromatic, flavoring, medicinal, antiseptic, antiviral, anti-inflammatory, and many other properties.

Custom extraction services from a toll processing partner puts botanical and herbal processing expertise in the hands of companies looking for the best ways to extract essential oils from fresh or dried plant biomass and create product formulations that deliver many benefits to their end users.

Essential oils, especially their volatile components, are the substances that give aromatic plants their characteristic scents and flavors. (Volatile oils evaporate readily at room temperature, while non-volatile oils have a slower rate of evaporation.)

Major industries that use essential oils include pharmaceuticals and nutraceuticals, food and beverage, personal care, cosmetics, home care, and even industrial and agricultural chemicals. Markets for these products are expected to grow as research into their benefits and applications continue, and with increasing consumer preferences for natural products.

High-value essential oils, concretes, and absolutes can be made up of more than 200 volatile and non-volatile constituent components. They are extracted from biomass that can include any or all of the parts of a plant, including:

• Roots
• Flowers
• Fruits
• Leaves
• Stems
• Seeds
• Bark

A few examples of popular and useful essential oils and extracts include:

• Lavender
• Peppermint
• Hemp extract
• Vanilla
• Citronella
• Pine
• And many more

There are several extraction methods commonly used to obtain the beneficial oils from plants. What’s the best extraction method? The answer to this question depends on the plant, the volume of biomass and production scale, the intended end use of the product, and more. This can be a critical question, especially in the context of hemp processing services.

In this article, we’ll review the top four ways to extract essential oils from plants, and how a toll processor can help you optimize essential oil extraction for cost-effectiveness and efficiency.

Conventional and Advanced Extraction Methods

Humans have been developing and refining extraction methods for essential oils for thousands of years. The ancient Egyptians, Chinese, Indian, and Greek cultures all have records of using aromatic oils for perfume and/or medicine. 

These oils have long been used for pharmacological properties that can include anti-inflammatory, antioxidant, and anticarcinogenic effects. Antimicrobial properties can include antibacterial, antifungal, and antiviral activity. Of course, many essential oils are also used to impart pleasant scents or flavors to foods, drinks, and other products, and can have relaxing or calming effects on users, as in aromatherapy.

The most common extraction methods include conventional and also newer, more advanced technologies. Conventional methods include cold pressing (or expression), distillation, and solvent extraction. 

Supercritical and subcritical carbon dioxide (CO2) extraction methods are more advanced and especially useful for the growing hemp processing industry.

1. Distillation

Simple distillation involves boiling water to vapor and allowing the steam to flow through biomass before condensing in a collection vessel. Because simple distillation subjects products to high temperatures, it can be a poor choice for heat-sensitive products — which includes volatile oils.

Steam distillation is the most common extraction technique for essential oils. In a still, pressurized steam is passed through the biomass, where it ruptures the plant structures that hold the essential oils, releasing constituent volatile and non-volatile compounds. 

The resulting liquid is condensed and naturally separates into two layers: essential oil and hydrosol. Examples of familiar hydrosols include rosewater and orange flower water.

In steam distillation, care must be taken to control pressure and temperature to avoid degrading the essential oils in the process of extracting them. Depending on the plant, steam distillation can take anywhere from a few hours to several days to fully distill oils from the biomass.

2. Cold Pressing (also called Expression)

Cold pressing is a traditional method that’s used for many oils that degrade when exposed to heat, such as lemon, orange, and grapefruit. This very simple extraction technique involves scraping or pricking the biomass, usually fruit peels, before pressing and rinsing the oils away using water. The water and oils are then separated.

Cold-pressed oils retain natural flavors, colors, sterols, and vitamins. But not all plant biomass is suitable for cold pressing, many constituents can be left behind within the biomass, and it is not efficient for high-volume extraction.

3. Solvent Extraction

Solvent-based extraction can use ethanol, methanol, or any of several petroleum-based hydrocarbon solvents, including:

• Hexane
• Pentane
• Acetone

The solvent, selected for its affinity with the desired plant compounds, flows through the prepared biomass to penetrate the plant structures and release the essential oils. The resulting mixture of solvent, plant oils, and botanical solids is typically filtered and vacuum distilled to remove as much solvent as possible, especially when petroleum-based hydrocarbons are used. A small percentage of chemical solvent residue can remain in the final product.

Vanilla extract is an example of a commonly used solvent extraction. The essential oils from the plant remain in alcohol, which was used to extract the desirable aromatic compounds from the structures of the vanilla bean pods.

4. Supercritical and Subcritical CO2 Extraction

The use of carbon dioxide as a solvent is in high demand, especially industrial hemp extraction services, to produce high-quality full-spectrum and broad-spectrum CBD extracts. In CO2 extraction, the carbon dioxide is subjected to specific temperature and pressure conditions to achieve specific effects. 

Whether supercritical or subcritical, CO2 works as a highly “tunable” solvent. This means that variables can be adjusted to most effectively extract targeted compounds, leaving behind the undesirable constituents in the biomass.

What is the difference between supercritical and subcritical CO2? In short, the difference is in pressure and temperature. Above critical temperature and pressure, CO2 becomes a supercritical fluid, which means it has properties of both a liquid and a gas. These properties enable the CO2 to penetrate raw hemp biomass and break down the plant structures to release important compounds, including cannabinoids and terpenes.

Subcritical CO2 extraction works similarly, though it can be a slower, less efficient process that results in lower overall yields. However, subcritical CO2 is gentler on some of the more delicate active constituents of the hemp plant. For producers of full-spectrum and broad-spectrum cannabis extracts, this is crucial for producing a whole-plant extract that delivers the “entourage effect.” Depending on the targeted compounds and the desired final product, subcritical CO2 may be the preferred extraction technique.

In both methods, after extraction, pressure and temperature are allowed to return to ambient levels and the CO2 evaporates, leaving no solvent residue, for a pure, unadulterated final product. Unlike other solvents, CO2 is environmentally friendly, nonflammable, and nonhazardous. 

CO2 extraction processes are more efficient, less energy intensive, and even less costly than some of the other methods. They’re also suited to scale up to high-volume production.

Creating Finished Herbal Extract Products

Most products of the botanical extraction process are liquids: oils, hydrosols, or tinctures in a base of alcohol or glycerin. But they may also be waxy extracts that are solid at room temperature.

After your toll processor has finished your extraction project, you may need additional steps to create fully commercialized products for your end users — so it’s worth having the conversation with your tolling partner about their capabilities to help transform botanical extracts into finished products. These services can include:

• Product formulation R&D
• Testing and analysis
• Liquid blending
• Emulsifying
• And more

Bottling and Repackaging Herbal Extracts

Minimizing time to shelf, freight, logistics, and other costs can be key to success in nutraceuticals, cosmetics, food, and beverage. So if your toll manufacturer can help you take your final, blended products from bulk formats to consumer or end-user packaging, the savings you realize in time, efficiency, and cost can make a real difference to your bottom line.

Be sure to ask whether your tolling partner can also offer fully automated, high-speed, cGMP-certified bottling of your liquid and liquefiable herbal extract products. Herbal and botanical extracts can end up in broad range of value-added products and formulations, including:

• Extracts and tinctures in dropper bottles
• Lip balms and salves
• Lotions and creams
• Body oils
• Herb-infused drinks
• And more

A toll processor that you can trust to achieve top-quality extracts, formulate in-demand products, and bottle and repackage for your end-user can help you deliver on your own brand promise of quality.

Learn more about herbal and botanical extraction and processing, and what to look for in a toll processing partner, when you download our eBook, Biomass to Bottle: CO2 Extraction, Blending, Bottling & More. Just click the link below to get your copy.