Manufacturing essential oils

Various methods are used in the extraction and manufacturing of essential oils, based on the type of botanical material.

The extraction process is one of the key factors that determine the quality of the oil. A poorly executed extraction can damage the essential oil and alter its chemical signature. The oldest method is undoubtedly extraction by oil infusion. Contemporary extraction processes are distillation, expression and solvent.

1. DISTILLATION EXTRACTION PROCESS

Three tubs are linked by small tubes. The first tub contains water and the second tub contains plants. Water is slowly heated up and the resulting steam travels through the tub and absorbs the plant material's active substances. It then passes through a cooling system—a long pipe coil immersed in a cold water basin. This cooled steam condenses into droplets and flows into the third tub: the essence tub. Essential oils being lighter than water, they can easily be "scooped up" from the surface. As for the water collected in the essence tub, it will be used to make floral waters and hydrolats.

Distillation requires heat, and heat is not suitable for very fragile plant material, or where the oils are difficult to extract. Both temperature and duration of exposure to heat must therefore be carefully controlled in order not to damage the oil.

This extraction process includes four main approaches: water distillation, steam distillation, hydro diffusion and water-steam distillation.

Water Distillation

When manufacturing essential oils using water distillation, the botanical material is completely immersed in water and the still is brought to a boil. This method protects the oils to some degree since the surrounding water acts as a barrier to prevent overheating.

When the condensed material cools down, the water and essential oil are separated. The water separated by this process is marketed as “Floral Water” (also called Hydrosol or Sweet Water) such as Rose Water, Lavender Water, Orange Water, etc.

Water distillation can be performed with reduced pressure (under vacuum) to decrease the temperature to less than 100 degrees, which helps protect both the botanical material and the essential oils. Neroli oil, which is sensitive to heat, is successfully extracted using this method.

Any botanical material that contains high amounts of esters does not react well to this extraction method, since extended exposure to hot water will start to break down the esters in the resultant alcohols and carboxylic acids.

If extended exposure to hot water is not recommended for a particular plant (such as Lavender), it is preferable to use a different extraction method.

Steam Distillation

Steam distillation is the most commonly used method for manufacturing essential oil. It involves pushing steam through plant matter in a still.

The hot steam helps release the aromatic molecules from the botanical material by forcing open the cavities where the oil is kept. The molecules of these volatile oils then escape from the plant material and evaporate along with the water. The temperature of the steam needs to be carefully controlled: just enough to make the plant material release the essential oil, yet not too hot as to burn the plant material or the essential oil.

The steam, which then contains the essential oil, is passed through a cooling system—a long pipe coil immersed in a cold water basin—to condense and become a liquid from which the essential oil and water is then separated.

The steam is produced at greater pressure than the atmosphere and therefore boils at above 100 degrees Celsius, which helps extract the essential oil from the plant material faster and therefore prevents damage to the oil.

1. Combustion chamber  2. Boiler  3. Flower bowl  4. Condensation drip valve 
5. Gooseneck  6. Cooling coil  7. Hot water outlet  8. Cold water inlet 
9. Essence jar for decanting the essence and the hydrolat

Hydro Diffusion

Hydro diffusion is a type of steam distillation. The difference lies in the way the steam is introduced into the still. With hydro diffusion, the steam is fed in from the top onto the plant material instead of from the bottom as in regular steam distillation. The condensation of the steam mixture containing the oil occurs below the area where the botanical material is held in place by a grill. The advantages of this method are: less steam used, shorter processing time and higher oil yield.

Water-Steam Combination Distillation

The plant material is immersed in water in a still, which has a heat source, and live steam is fed into the water and plant material mixture.

2. EXPRESSION EXTRACTION PROCESS

The expression method is referred to as “cold pressing”, since no heat is involved. Most nut, seed and citrus essential oils are extracted using a “cold pressed” method which generally produces good quality oil. In this method, the oil is forced from the plant material under high mechanical pressure.

Of all expression extraction processes, the most popular method is undisputedly sponge expression. In the past, this was done by hand. The fruit pulp was removed along with the rind and pith, then soaked in warm water to make the rind more pliable. The fruit absorbs the water and becomes more elastic. It is inverted to rupture the oil cells and a sponge is placed next to the rind. It is then squeezed to release the volatile oil, which is collected directly into the sponge and into a vessel, before being decanted.

3. SOLVENT EXTRACTION PROCESS

Solvents such as petroleum ether, methanol, ethanol or hexane are used to extract essential oil from fragile botanical material like jasmine, hyacinth, narcissus and tuberose, which cannot sustain the heat of steam distillation.

A solvent extracted essential oil is highly concentrated and is very close to the natural fragrance of the botanical material used.

Although solvent extraction is used extensively, some people do not believe that it should be used for aromatherapy essential oils since a residue of solvent could be present in the final product.

After the plant material has been treated with the solvent, it produces a waxy aromatic compound called “concrete”.

Various techniques are used in solvent extraction: maceration, enfleurage and hypercritical carbon dioxide CO2.

Maceration

In the maceration method, the flowers are soaked in hot oil to rupture their cell membranes. The hot oil then absorbs the essence, before it is cleared of the botanical material and decanted. This is very much the same technique as solvent extraction, with the difference that maceration uses hot oil instead of solvents.

Enfleurage

Framed glass plates are covered with highly purified and odourless vegetable or animal fat and the petals of freshly-picked flowers are spread across the glass plates and pressed in this fatty bed. The petals remain in this greasy compound for a few days to allow the essence to disperse into the compound. Then the depleted petals are removed and replaced with new ones.

This process is repeated until the greasy mix is saturated with the essence. When the mix has reached saturation, the flowers are removed and the enfleurage pomade —the fat and fragrant oil— is washed with alcohol to separate the extract from the remaining fat, which is then used to make soap.

As soon as the alcohol evaporates from the mixture, we are left with the essential oil. This extraction method — used to create high-end perfumes — is labour-intensive and very costly. Nowadays, this process is sometimes used to extract essential oil from tuberoses and jasmine.

Hypercritical Carbon Dioxide gas (CO2)

The use of hypercritical carbon dioxide is new for extracting essential oils from botanical material. Although expensive, it does yield good quality oils.

At 33º Celsius, carbon dioxide becomes hypercritical, that is: not really gas nor liquid but with qualities from both. It is an excellent solvent for the extraction of essential oils as it requires low temperature and the process is nearly instantaneous. Furthermore, carbon dioxide is inert and therefore does not interact chemically with the extracted essence. Removing the carbon dioxide solvent simply requires to depressurize it.

This process must take place in a closed chamber to create the hypercritical pressure required for carbon dioxide: 200 atmospheres— 200 times the average, sea-level atmospheric pressure. Heavy-duty stainless steel equipment is a must to achieve this type of pressure. Therefore, high capital investment is required for this extraction method.