First of all – what IS a carrier oil? A carrier oil is a vegetable oil derived from the fatty portion of a plant – which is usually the seed, kernel or nut of the plant. Since essential oils are so concentrated and can burn the skin when applied undiluted, essential oils are generally used diluted in a carrier oil base; the term “carrier oil” is derived from the oil’s purpose in carrying the essential oil to the skin.
Just like with essential oils, carrier oils should be stored in a cool, dark place away from direct sunlight to best retard rancidity and extend their shelf life. While it is not really necessary to store carrier oils in amber bottles, a cool location, and maybe even the refrigerator (although not the freezer!) will work well. Some of the oils will solidify in the refrigerator, but can easily be gently warmed and lightly stirred or shaken before use.
While essential oils do not generally become rancid, carrier oils can become rancid over time. Various factors will effect how rapidly that occurs, including how they are stored, how they were extracted, antioxidants added to retard rancidity (T-50, etc.), and the type of oil you are storing. Other means of increasing the shelf life of your carrier oils include:
-Do not keep bottles partially full – This is because the oxygen that lives in the bottle reacts with the oil and starts to oxidize it, causing it to go rancid more quickly. The empty space inside the bottle is the “headspace” and the best way to retard rancidity is to limit the amount of headspace.
-Keep your bottle caps tight – This is for the same reason that you want to avoid keeping bottles partially full; you are trying to keep oxygen out of your carrier oil bottles. Exposure to oxygen will shorten the shelf life of your oils. Plastic bottle lids can crack if overtightened, allowing oxygen in, but closing them tightly enough to keep oxygen out without cracking the lids is always a good idea.
-Don’t contaminate the oil – Another thing that will destroy a carrier oil quickly is exposure to contaminants. This would include unsterilized fingers and measuring equipment, cotton balls, syringes, eye droppers, and the like. It’s generally best to pour a portion of the carrier oil into another container and work with it from there (without reintroducing the excess oil to your storage bottle) than to risk contaminating the original oil in your storage container.
-Also, please remember that oils are flammable and keep them away from heating elements, etc. Many fixed oil purchasers also find it handy to label their carrier oils when they get them with the date purchased and the name of the oil, just in case the original label wears off or becomes unreadable.