28 November 2008

Essential oils will not begin to smell or rancid like vegetable (carrier) oils over time. But, many essential oils essential oils can oxidize, deteriorate, lose their therapeutic properties, and lose the aromatic quality as time passes or if they are not stored properly. Your nose will tell you that something is seriously wrong long before the point when the oils become unsuitable to be added to carriers for use on the skin. People who use adulterated or synthetic oils need to worry about shelf life. Some British references on aromatherapy say you should throw away your oils every six months and purchase a fresh quantity.

The shelf life of essential oils varies from one oil to the next, from batch to the next and from supplier to the next. But most have a shelf life of a year or more from the date purchase provided from a reputable supplier that maintains fresh inventory.
Factors that can directly affect the shelf life of an essential oil :
  • The method of distillation
  • The conditions and care used during the distillation
  • The quality of the botanical used
  • The care in bottling, storage and handling of the essential oil
  • The storage conditions of the oil
  • Heat, sunlight and air can all have a detrimental effect
Chain Reaction
The shelf life of an essential oil is governed by its chemical stability, and anything that interferes with this stability will cause the oil to start the slow, but inexorable process of deterioration known as oxidation. Once the process of deterioration has begun it can not be stopped, and like a chain-reaction it gathers speed according to the intricate balance of the oils chemical constituents.

Heat, sunlight and air can all have a detrimental effect on the chemistry of all the oils that are used in aromatherapy, and this also includes carrier oils and mixtures of both such as massage oil blends. In addition, the complex and varying chemistry of natural essential oils means that the rate of deterioration will be different for every individual botanical species of oil, even when kept under ideal conditions.

This means that some oils will last far beyond what many books report, whilst others may deteriorate much earlier than they claim. Either way, it is the combination of heat, air, the chemistry of the oil and the way they are stored that will ultimately dictate how long your oils remain in good condition. I did say it was not straightforward!

This is why dark colored glass bottles are used to package essential oils, since they offer some protection to the oil from the sun's harmful ultra-violet light. However, these simple house-keeping practices must still be observed if the bottles are to have any chance of doing their job properly.

The shelf life of essential oils can be maximized by storing them in :
  • Dark glass bottles
  • Tighly closed
  • Keeping them in a cool, dry location away from sunlight
As you use up the oil from a large bottle, rebottle the oil into a smaller bottle. This reduces the amount of oxygen that stays in contact with the oil.

See the Essential Oils storage article for more information.

The complex and varying chemistry of natural essential oils means that the rate of deterioration will be different for every individual botanical species of oil, even when kept under ideal conditions. This means that some oils will last far beyond what many books claim, whilst others may deteriorate earlier than stated.

Guidelines for Telling if an Essential Oil Has Deteriorated
  • The aroma has drastically changed
  • The essential oil has thickened
  • The essential oil has become cloudy
In order to discuss shelf life, we need to distinguish between various classes of scented oils. There are four types of fragrant oils to consider :
  • Essential oils (distilled)
  • Expressed oils (usually citrus)
  • Absolutes (solvent extractions); and
  • Carrier Blend Oils (essential oils in a fatty base)
The shelf lives of these four classes of aromatic oils are different. While expressed, absolute, and carrier blend oils contain large molecules along with their small aromatic ones, pure essential oils obtained entirely by distillation contain only small molecules.

Large molecules tend to be less stable than small ones. Shelf life addresses the question of chemical stability. Aromatic oils are mixtures of many compounds. The large molecules of fatty vegetable oils are not as stable as the tiny ones that comprise essential oils.

If a mixture of compounds remains stable, that is, if it does not decompose or change its chemistry over a long period of time in storage, we say it has a long shelf life.
Essential oils have been found in Egyptian tombs that were still aromatic and effective their therapeutic properties intact, even after thousands of years. These oils were in moderately cool, dark places tightly sealed from exposure to air and the elements. That is all they required to maintain their potency.

You can tell if any damage has been done to your oils by heat by testing the fragrance. If it still smells the same as when you bought it, it is still okay. If not, then damage has occurred. Exposure to heat in excess of 90-120° F can shorten the shelf life of expressed, absolute, and carrier blend oils, but does not shorten the shelf life of true essential oils.

Essential Oils (distilled)
All steam distilled essential oils have a shelf life of at least 2 years, and even more when stored properly. Tea Tree, Pine and Fir oils are the above exceptions, and typically have a shelf life of around 12 to 18 months due to certain components in their natural chemical composition.

A number of blends containing pure essential oils used in North America also contain some fatty oil such as olive, sesame seed, or almond. Usually, 80% or more of these blends consist of essential oils. These are not the same as the aromatherapy grade massage oils of England which are mostly fatty, but they do have a shelf life.

Expressed Oils
Cold pressed citrus oils have the shortest shelf life of all essential oils due to a high proportion of components called terpenes. Terpene-rich oils tend to oxidize the quickest and can have a scant shelf life of 6-12 months. Therefore extra care should be taken to store them safely away from sources of heat. If they were fresh when you purchased them from your supplier, you can expect citrus oils to remain in good condition for 6 to 12 months, and even longer when cared for properly. If you normally buy them in 10ml sizes, immediately decant them into two 5ml bottles and this will protect one bottle from oxidizing for longer.

Expressed oils, absolutes, and carrier blend oils are sensitive to heat, such as in a car on a hot day. Heat accelerates any chemical reaction and if the large molecules in these oils are prone to gradual decomposition even at normal temperatures, this process will be hastened by heat.

Absolutes & Phytonics
Absolutes and phytols generally have the longest shelf of all oils, often remaining in good condition for up to 5 years and beyond.

The longest-lasting oils, which improve as they age, tend to be the thick resins such as frankincense and myrrh, woods such as sandalwood, roots like vetiver, as well as other oils, including spikenard and patchouli. Keep well stocked on these oils so that they have time to mature nicely before you begin to use them

Carrier Blend Oils
See the Carrier Oil Shelf Life article for more information.

Fatty oils also contain proteins, polypeptides, and amino acids, unstable compounds not found in essential oils. Fatty oils will naturally break down into smaller molecules over time at normal room temperatures. It’s call “going rancid”.

While large molecules have no smell, the smaller molecules resulting from the decomposition of fatty hydrocarbons do have a smell, an unpleasant one. Hence, an aromatherapy grade oil that is mostly vegatable oil does have a shelf life. Thus, the British texts that recommend pitching your oils every six months have a valid point in reference to “aromatherapy grade” oils.

Absolutes, expressed oils, and oil blends that are mostly essential and only partly fatty all have a shelf life. Experience has shown that their shelf lives can be measured in years, unless the oil has been exposed to excessive heat. So if you have any such oils, your nose will know if they go bad.
If you want to extend the shelf life of essential oils that have fatty oilsin the mixture, refrigerate them. However, if you are using such oils over periods of time less than a few months, you don’t need to go to the trouble of storing them in your refrigerator.

You don’t have to refrigerate pure essential oils that are the products of distillation. Refrigeration does not extend their shelf life. A cool environment won’t hurt them or help them. They will last indefinitely at normal living temperatures and will remain unaffected and intact even when occassionally exposed to the heat of a hot day in a car, provided you do not open the bottle until it has cooled down to normal temperatures.

See the Essential Oils storage article for more information.
See the Do you still want to buy cheap essential oils? article for more information.

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