Preservation of Essential Oils
This is usually one of the first questions asked by those who are new to the world of aromatherapy. It is truly worth knowing what should and shouldn't be done in this regard. Why? The way you handle essential oils affects their longevity, so it's important to learn a few things about it. Proper storage is definitely the key to getting the most out of your oils. Some oils (especially citrus ones) do not like extreme temperatures or sudden changes. Therefore, we must ensure that they do not lose their aromatic and therapeutic qualities.
Firstly, essential oils should preferably be bottled in dark amber or cobalt blue glass containers, as these protect the oils from UV rays. Never leave the oils where they can be exposed to direct sunlight.
Bottles & other containers for Essential Oils
A Dark, Cool, and Dry Place for Essential Oils
Essential oils should be stored in cool, dry places, completely protected from light and heat, in well-closed and sealed bottles that do not allow air in. The storage place should be properly ventilated.
Being moderately volatile, essential oils evaporate relatively quickly, so they should never be left open and should be stored immediately after use. If you plan to store them for a long period or during extreme heat (many months), make sure the caps are tightly closed and the pipettes are removed to achieve an airtight seal. This prevents the oils from evaporating and permeating the storage space with their scent.
The Importance of Proper Storage for Safety
Another important reason to store oils properly is safety: It is extremely important to keep them locked away and completely out of reach of children. Despite being natural products, many of them can be very dangerous in a child's hands, especially if ingested.
Citrus Essential Oils: Best Kept Cold
Citrus essential oils are more prone to oxidation, so to avoid continuous temperature fluctuations, it's best to keep them refrigerated at a constant temperature between 5 and 10°C. Some oils, like star anise or fennel, may solidify at low temperatures, but that's okay; just let them warm up to room temperature for a few minutes.
Storage Cases for Essential Oils
If you don't have space to store the oils in the fridge or refrigerator, consider storing them together in an essential oil case, protected from extreme temperature changes and bumps, cushioned in foam. This also makes it easier to keep them out of reach of children.
A Bit of Chemistry...
Essential oils are complex substances. Their medicinal properties originate from components such as monoterpenes and sesquiterpenes. These are compounds consisting of 10 (mono) or 15 (sesqui) carbon atoms, which can also have an oxygen atom attached in the form of alcohol, aldehyde, acid, or ketone. They also contain a few weak carbon double bonds characteristic of unsaturated fatty acids. When monoterpenoids and sesquiterpenoids are exposed to air, they undergo an oxidation process: alcohol is transformed into aldehyde, and aldehyde can transform into acid. Sounds familiar? This is the same process responsible for spoiling wine and turning it into vinegar when accidentally exposed to air during storage.
Some monoterpenoids, such as geraniol (found in essential oils like geranium Pelargonium graveolens and grapefruit Citrus Paradisi), are more prone to oxidation. Others, like linalool (found in essential oils like lavender), are more stable. Additionally, the carbon double bonds can also become single and trap oxygen atoms, forming oxides, epoxides, and peroxides.
The Smell of Rancid Vegetable Oil
Have you ever had vegetable oil turn rancid in your pantry? That particular smell reveals the same chemical process. Almost all constituents of essential oils are unsaturated compounds containing carbon, so they can undergo the same reaction, spoiling or oxidizing. Although unpleasant odors are not perceived in essential oils, they should be avoided if they have undergone oxidation.
The Dangers of Oxidation
With rare exceptions like patchouli, sandalwood, and vetiver, oxidation spoils essential oils and degrades their aromatic quality and therapeutic properties. Moreover, it leads to the formation of skin irritants and potential allergens. Exposure to oxidized essential oils can cause skin rashes and more serious allergic reactions. There is a relationship between the oxidation of essential oil components and their ability to trigger allergic reactions. For example, it has been shown that geranial - an oxidized product of geraniol (found in geranium P. graveolens essential oil) - is much more likely to cause reactions than the compound it comes from. In the case of tea tree essential oil, the epoxides formed after exposure to air were identified as allergens. It's no surprise that reactions caused by stored and oxidized oil were stronger than those caused by fresh, well-preserved, and non-oxidized oil. Similarly, when lavender essential oil is exposed to air, linalyl acetate oxidizes, creating peroxides and epoxides that are potential allergens.
In Summary...
Use dark containers
Preferably made of quality glass for long-term storage. Keep them out of direct sunlight whenever possible.
Store in a cool place
Especially citrus oils from cold extraction. Also for long-term storage.
Avoid oxidation
Do not leave bottles open for long periods. Store in a cool, dry place.
Keep out of reach of children
Use a safe place to store your essential oils. This way, you'll not only preserve your oils but also protect the little ones.