Shelf life of essential oils affects the properties and usability of oils. Shelf life of each bottle of essential oil may be different because a large number of factors affect the shelf life. Read on further to learn about the what factors affect the shelf life and how to improve it.
Essential oils do not expire in the traditional sense, means they do not turn rancid. However; they degrade their aroma quality and lose their therapeutic values over period of time and may become ineffective for applications like aromatherapy.
Over a period of time, essential oils on exposure to heat, light and oxygen undergo oxidation, polymerisation and resinification processes that lead to change in chemical composition of essential oils. This changed chemical composition lead to changes in the properties of essential oils and make them ineffective. The process of oxidation begins when the oil is distilled; therefore, shelf life is determined by distillation date and not when it is purchased.
There are some exception like patchouli, sandalwood and vetiver essential oils.
Oxidation of essential oils change the chemical composition of essential oils. This lead to changes in its properties including change in aroma, colour, viscosity.
However, at times these changes might not be easy to detect and experience is required to figure out the difference.
Shelf life of essential oils may vary from one botanical to the next, from one distillation to the next, and from one supplier to the next. It may even vary from one bottle of oil from the same batch of production to another. It is because shelf life of essential oil is affected by a number of factors. Even the factors like composition and quality of biomass used for distillation, distillation method, handling and storage affect the shelf life of essential oils. Let’s look at some of the factors that may determine shelf life of essential oils.
On exposure to oxygen, monoterpenoids and sesquiterpenoids undergo oxidation and alcohol is transformed to aldehyde, aldehyde may turn into acid.
According to some studies, extreme heat change the chemical structure in the essential oil. While there doesn’t seem to be concrete proof of this yet, makers are careful about the temperature of the room in which the essential oils are stored.
Exposure to light, especially visible and Ultraviolet (UV), are considered to accelerate auto-oxidation processes. Monoterpenes have been shown to degrade rapidly under the influence of light. A study done with Sweet Orange essential oil shows that exposure to UV light for about 50 minutes leads to dramatic changes. Some of its chemicals were increased, and some were decreased. The most shocking thing is that there were 12 new chemicals present in the oil.
The biggest factor that contribute to shelf life of an essential oils is it chemical compositions. For example, essential oils high in monoterpenes will undergo oxidation faster in comparison to essential oils high in sesquiterpenol. Depending upon chemical constituents, essential oils may fall into different chemical families. Some of the main chemical families are monoterpenes, sesquiterpenes, monoterpenols, sesquiterpenols, aldehydes, esters, oxides, ketones, and phenols.
As discussed above, the biggest factor contributing to shelf life of essential oil is its chemical composition. Following is a general guideline for shelf life of various chemical families of essential oils.
Monoterpene are found in all essential oils and have a structure of 10 carbon atoms. These compounds oxidised in the presence of heat and air. Shelf life of monoterpene rich essential oils is generally 2-3 years (some a bit longer). It is important to store monoterpene rich oils well, sealed tightly, away from heat & light.
Some of the oils high in monoterpene are lemon, sweet orange, siberian fir, ravintsara, juniper berry, grapefruit, frankincense, cypress, black pepper and bergamot.
Sesquiterpenes consist of 15 carbon atoms and have lower volatility and higher boiling points than monoterpenes. Shelf life of sesquiterpene rich essential oils is 8-10 years or longer. Some of the essential oils rich in sesquiterpenes are cedarwood, vetiver, patchouli, opopanax, myrrh, and ginger.
Aldehyde rich oils can be irritating to the skin, especially if oxidized. They are middle notes with a typical lemony aroma. Shelf life of aldehyde rich essential oils is 4-5 years. Some of the essential oils rich in aldehydes are melissa and lemongrass.
Shelf life of ketone rich essential oils is 5 -7 years. Some of the essential oils rich in ketones are thuja, spike lavender, sage, pennyroyal, mugwort, hyssop and clary sage.
Shelf life of oxide rich essential oils is 3-5 years. Some of the essential oils rich in oxides are rosemary, laurel leaf and eucalyptus.
Shelf life of ester rich essential oils is 5-7 years. Some of the essential oils rich in esters are wintergreen, roman chamomile, helichrysum, jasmine absolute and birch.
Shelf life of ether rich essential oils is 5-7 years. Some of the essential oils rich in ether are tarragon, nutmeg, fennel, anise.
Essential oils are usually expensive and if stored properly, their shelf life may be extended to use for longer period of time.
Essential oils should be stored tightly sealed in dark, coloured glass bottles, in a cool, dark place, out of direct sunlight and out of the reach of children and animals. In addition, exposure to fluorescent lighting should be avoided.
High temperatures accelerate the process of oxidation and reduce shelf life. Minimising the exposure to heat, shelf life of essential oils may be extended greatly. The ideal temperature to store your essential oils is 36-40° F (2-4° C).
Another way to improve the shelf life of essential oil is to store essential oils in small size bottles to limit their exposure to oxygen. In other words, limit the amount of oxidation of essential oils by keeping them in bottles that are filled to capacity in which there is no room inside the bottle for oxidation to occur.
Pure essential oils break down plastic and should never be stored undiluted in plastic bottles. Properly stored essential oils that have been sealed, unopened and kept in a cool, dark place will maintain their potency for many years. In addition, it is advised to avoid use of dropper caps instead of screw lids since plastic of the dropper can break down due to continuous exposure to the contents, spoiling your expensive essential oils.
It is advised to avoid the use of essential oils for aromatherapy purposes in case they are oxidised. Oxidised oil may cause skin irritation or sensitisation, which can cause skin rashes, burns, peeling skin, or other unpleasant side effects.
However, the oxidised oil may not be completely waste. They may still be used for cleaning blends, such as kitchen and bathroom disinfectant sprays, etc.
In addition to keeping safe storage of essential oils, it is prudent to use essential oils with precautions. Head over article to read the basic safety and dilution guidelines for safe use of essential oils.
The Essential Oils Complete Reference Guide
The Practice of Aromatherapy