(Photo Image: EssentialWellness.com)
Generally we dont query the source or form of extraction employed when we buy our face oil, body oil, cleansing oil, hair oil or any oil. Although having the knowledge at your finger tips is vaulable in case you doubt the quality of oil and have questions around its extraction processes. This edition intends to provide you with knowledge of various types of extraction employed for different ingredients so you can gauge the quality and integrity of the essential oil you’re using.
Oil extraction is a very complex area. I’m making a humble attempt to keep it high level and approach the topic with minimal jargon. By no means, I want to bombard you with information and kill your interest in this area. Having said that, here are some points to note:
- Different ingredients require different methods of extraction due to its individual properties
- Different methods of extraction determine the degree of quality for each oil (including consistency & texture of oils) especially when heat and additives are involved
The table below shows, each class of oil (as talked about in Edition 1) and appropriate methods employed:
|Carrier oil||Cold pressed, Expeller Pressed, Infusion, Centrifuge or Solvent Extracted|
|Essential Oil||Distillation (steam, vacuum and hydro), Cold Press, Solvent (although much debated method in Aromatherapy world)|
|Absolutes||Solvent or Enfleurage|
|CO2 Extracts||Hypercritical CO2 Extraction (not covered in this post)|
Cold Pressed or Expression – Think of cold pressed juices, similar concept adopted to extract oil from seeds, nuts, kernels etc. This method helps the oil maintain its original properties, constituents and depth. This method ensures no therapeutic benefits are lost to heat. Possibly the top quality oil you can lay your hands on.
Expeller Pressed – A small amount of frictional heat is produced which is created by hydraulic presses. This makes the oil suitable and economical as a base for cosmetics because of its fairly undisturbed molecular state.
Centrifuge Extraction – This method is generally used for Virgin Coconut oil, where the coconut milk is spun in the centrifuge machine (and the oil separates, similar to the way cream separates from milk). This process is repeated a few times before pure oil is obtained. During the process, the temperature is closely controlled and monitored to keep the ingredients characteristics intact.
Due to the absence of very high heat in the extraction process, the oil is pure and retains its properties. It has a very mild aroma; although any form of heating will intensify the scent. Analogy: Think of raw food, uncooked it has a mild scent, you cook it and the delicious aroma intensifies.
Solvent Extracted: Sometimes, with some seeds, nuts or kernels, it is necessary to use a solvent (an additive to enable extraction, examples include petroleum ether, methanol, ethanol or hexane) to extract oil in order to make the extraction costs effective.
Upon final oil extraction, the solvent is removed from the oil, but a trace of percentage of the solvent may still be present in the final oil. Coconut, Palm, Grapeseed and Rice Bran are typically solvent extracted.
Some fragile flowers like Jasmine, Hyacinth, Narcissus and Tuberose cannot handle the heat of steam distillation (explained below). Therefore, solvent extraction method is employed to ensure the botanical properties remain intact and not lost to high temperatures. Essential oil extracted under this method is concentrated and close to the natural fragrance of the ingredient.
Controversy – Whilst solvent extraction is used extensively, some strongly believe that essentials oils from this method should not be used in Aromatherapy since a residue of the solvent may be present in the finished product. Some reports suggest, solvent residue of 6-20% is still present in the final extraction, but this was the case when Benzene was used as a solvent (no longer used as solvent as it is regarded as carcinogenic). Although, Hexane (a hydrocarbon) as a solvent, the residue goes down to about 10ppm (parts per million) and it is considered to be extremely low concentration of residue in the final product. After the ingredient has been treated with solvent, it produces a waxy aromatic compound called “concrete”.
Infusion/Macerate: This extraction method entails “infusing” the ingredients with the fat soluble properties of other botanicals. The ingredient selected is gently bruised and soaked in base oil for a set duration of time (something like bruising meat and then marinating). In some instances, the base oil is gently heated to encourage infusion. The composition is then filtered and additional material may be infused in the same oil a number of times (makes it more cost effective). The final oil is thoroughly filtered again to ensure any traces of plant particles are eliminated. The benefit of using oils from this extraction process is that the infused oil will contain the therapeutic properties of both the ‘marinating’ oil and original plant material.
Enfleurage (cold fat extraction process) – This method is usually adopted for flower petals that continue to give aroma even after harvesting. The petals remain in a greasy compound (animal or vegetable fats) for a few days or a couple of weeks (depending on the ingredient used) to allow the essence of petals to disperse into the compound.
Over a period of time the depleted petals are removed and replaced with a fresh harvest of petals. This process is repeated until the fatty compound mix is saturated with the essence. This process is repeated couple of times until the optimum saturation is achieved. When the mix has reached the saturation point, flowers are removed and the ‘enfleurage pomade’ – the fat and fragrant oil are then washed with alcohol to separate the extract from the remaining fat, which is then used to make soap. Long before the solvent extraction method was popular, flowers were extracted with enfleurage method in the Grasse region of Southern France.
As soon as the alcohol evaporates from the mixture you are left with the essential oil. This is a very labor intensive method of extraction, and needless to mention very costly way to obtain essential oil. Jasmine and Tuberose essential oils are extracted with this method. Today, Grasse continues to be one of the few areas in the world that continues to employ enfleurage as a method of extraction, although it is rare in the aromatherapy market due to the expense. If one finds a Jasmine enfleurage on the market, this would typically be considered an absolute (Source: Naha Org).
(Photo Image: Union-Nature.com)
In the distillation process, ingredient is placed on a grid inside the still. The still is then sealed and depending upon the methods employed, steam or water slowly breaks through the ingredient to remove its volatile components. These volatile components rise upward through a connecting pipe that leads them into a condenser. The condenser cools the rising vapor back into liquid form. The liquid is then collected below the condenser. Since water and essential oil do not mix, the essential oil will be found on the surface of the water where it is drained. In some instances like that of Clove essential oil, the oil is heavier than water and is found at the bottom rather than the top.
1.Water distillation – The ingredients are completely immersed in water and the mixture is brought to a boil. The advantage of employing this method is the water acts as a barrier to prevent it from overheating and losing its properties. When the mixture cools down, the water and essential oil is separated and oil is decanted.
As a part of this process, the water that is separated is used, marketed and sold as ‘Floral Water or Hydrosol’ such as Rosewater, Orange Blossom water.
Water distillation can also be done at reduced pressure (under vacuum) to reduce the temperature to less than 100 degrees, which is beneficial in protecting the ingredients and the essential oils. As an example: Neroli oil is sensitive to heat and therefore will be successfully extracted using this method. Flip Side: Some ingredients contain high amounts of esters that don’t work well with this form of extraction. With extended exposure to hot water, the ingredient will start to break down the esters resulting in alcohols and carboxylic acids (e.g. Lavender).
2. Steam distillation – The ingredient is placed in a still and steam is introduced in the still. The hot steam enables release of aromatic molecules from the ingredient as the steam forces open the pockets where the oils are stored in the plant. These molecules are volatile oils which escape the plant and evaporate into steam.
The temperature of steam is rigorously controlled to ensure its just right to obtain the essential oil without impacting its integrity. If the temperature is too hot it may burn the plant and essential oil.
The evaporated steam (contains essential oil) is passed through cooling system to condense the steam. The resulting liquid separates water and essential oil.
Lavender is heat sensitive (thermolabile) and with this extraction method, the oil is not damaged and ingredients like linalyl acetate will not decompose to linalool and acetic acid.
Hydro diffusion (a type of steam distillation) – A relatively newer method of distillation, used for extracting essential oils from tough/solid materials like wood barks or seeds. The underlying difference between Hydro and Steam distillation method is the way steam is introduced in the still on the ingredients being extracted:
- Hydro Diffusion – steam is introduced from top
- Steam Distillation – steam is introduced from bottom
The condensation of the oil containing steam mixture occurs below the area where the ingredients are held in place by a grill. The main advantage of this method is that less steam is used (ensuring properties remain intact), shorter processing time and a higher oil yield.
Based on this information, you may be able to understand and appreciate why we pay so much for good quality, ethically sourced oils. My next post in thi series will unravel the worst kept secret: Why I prefer oils over moisturizers.