Most, if not all carrier oils you buy undergo some level of refinement. Refining may be as simple as removing seed particles and dirt or solid bits of olive, to complex chemical refinement.
Cold Pressing Process
Cold pressed oils, also known as cold expeller pressed oils, is a chemical free method whereby the oil has been mechanically pressed from the fatty portions of the botanical, while ensuring that the maximum temperature (caused by friction) does not exceed 120 degrees. The oil is horizontally pressed using a rotating screw and the friction that is created by rotating the paste mixture will generate heat internally. This rotation works to separate the oil from the juice and pulp. Many people use machinery with integrated centrifugal force to separate the distinct parts.
At the final step, the oil is filtered one last time to ensure any remnants of rind, peel or pulp have been removed.
Expeller Pressed
Expeller pressed oils are mechanically pressed from the botanical material at high pressure to obtain maximum yield. Not all expeller pressed oils are cold pressed as high pressure extraction can cause temperatures to rise above 120 degrees. However, unlike in cold-pressed oils, oils that have been extracted using expeller pressing do not have very low temperatures. Their temperatures usually rise above 120 degrees Celsius. Due to such high temperature, the oils need to be treated and processed properly, so that their nutrients are not damaged by the heat. Only if temperature is monitored and kept under 120 degrees, can the oil be called cold pressed. Otherwise it is simply called expeller pressed.
Solvent Extracted:
Sometimes it is necessary to use a solvent in order to extract the oil from certain seeds, nuts or kernels in order to make the extraction cost effective. Once the oil has been obtained, the solvent is then removed from the oil, but a trace percentage of the solvent may still be present in the final oil. Coconut, Palm, Grapeseed and Rice Bran are typically solvent extracted.
CO2 Extracted:
CO2 extracted oils are extracted using fluid carbon dioxide as the solvent. Carbon dioxide is converted to liquid using high pressure making it a safe and effective solvent that allows all the desirable active constituents of a plant to be collected without the risk of heat degradation. Once the extraction is complete, the pressure is released allowing the carbon dioxide to return to its natural gaseous state, leaving behind only the extracted essence of the plant. CO2 extracted oils are the closest representation of the natural plant ever achieved. CO2 total extracts include the volatile components as well as the heavier, waxy components that give plants their color, and are therefore thick and waxy in consistency.
Infusion/Macerate:
An infused or macerated oil is a vegetable oil that has been "infused" with the fat soluble properties of other botanicals. Plant material is bruised and soaked in a base oil for a set duration of time. The base oil is sometimes gently heated to encourage infusion. The material is then filtered. Additional material may be infused in the same oil a number of times. The final oil is then well filtered to remove any traces of plant particles. The benefit to using an infused vegetable oil is that the infused oil will contain the therapeutic properties of both the vegetable oil and the botanicals that were infused into the oil.
RBD:
RBD is the abbreviation for "Refined, Bleached and Deodorised." Within the description / extraction method for each of our vegetable oils, we note those oils that are refined, bleached or deodorised.
Refined:
Some oils undergo a refinement process in order to remove impurities, improve the colour or texture, or stabilise the shelf life of the oil. The oil is reacted with a weak base solution to saponify the free fatty acids into soap. The oil is then centrifuged and washed with water until the pure oil remains. The oil may also be degummed to remove the sticky phospholipids, colour pigments and odour lending portions.
Bleached:
Some lipids are bleached in order to improve the color and clarity of the oil. Bleaching is generally done by passing the oil through fuller's earth or clay and then filtering the oil.
Deodorised:
Some lipids undergo a deodorisation process in order to remove compounds that lend an unappealing or overpowering aroma to the oil. This is generally done by blowing high temperature steam through the oil to vaporize the aromatic components. This process is made more effective by heating the oil to high temperatures and performing this process under a vacuum to help remove all of the volatile odourous substances. Due to the high temperatures used, deodorisation is clearly the most damaging process of refinement.
Carrier oils are made through one of two processes: cold pressing, or expeller pressing. Cold pressed carrier oils are high in quality, and the resulting oil maintains many of its original nutrients.
Shelf Life
Most carrier oils will last anywhere from six months to two years, though much of their life is determined by how they are handled and stored. Exposure to air, heat and light will, over time, cause carrier oils to go rancid.
Rancidity happens when oxygen attaches to the unsaturated carbon fatty acid molecules, causing oxygenation and the oils become rancid. Oils are prone to oxygenation at different rates depending on their fatty acid structure. For example, oils high in saturated fatty acids, like shea butter, coconut oil, cocoa butter and mango butter hold up for multiple years in proper storage whereas oils high in polyunsaturated fatty acids, like flax seed oil, grape seed oil and raspberry seed oil will go off far more rapidly, approximately six months to one year.
The exact shelf life of oils varies considerably, but there are steps you can take to prolong the useful life of your carrier oils. Store all oils in a cool dark space and always keep lids on tightly. Dark bottles also help to keep your oils fresh longer as they minimise the action of light on the oils.
Very delicate oils, like flax seed oil, hemp and borage should be kept in the fridge while others should be fine in a cool dark space.
Should I buy Refined or Unrefined?
For most oils I look for a lightly refined oil, one that still has a lot of the scent and pigments present but are refined enough to make a good product.
But there are exceptions, for example argan oil. Argan oil, if it is not deodorised, can smell unpleasant and strong. But argan oil itself is such an important skin care oil we don’t want to leave it out of our recipes and routines and so, it is one oil that is often deodorised and is an example of good refining.
Another example of when you might want a more refined carrier oil is if you are creating an essential oil blend and you want the main focus to be on the scent combination of your essential oils. You’d want to pick a neutral, usually refined carrier oil that can carry your formula without overpowering the essential oils.
A common refined carrier oil is a partial oil, fractionated coconut oil or FCO. Fractionated coconut oil is scentless, colourless and tasteless. It has long shelf life and is a completely saturated, and liquid form of oil.
Personally, fractionated coconut oil not an oil that I use as I feel it is the junk food of of the lipid group, highly refined, characterless but it is convenient. Here’s a list of carrier oils that are neutral without being highly refined, ideal for when you want the main focus of your formula to be on other compounds and you need an oil that will hold your formula without a strong presence of its own.
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