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. 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.
If you are using pure distilled therapeutic
grade essential oils,
as described in Chapter One of this book, then you don’t
have to
worry about 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. No one knows what their true shelf
life
may be. All we know is that it is measured in millenia, not
months.
As for the British oils, there is a so called
aromatherapy grade
of oil that is actually only 1-5% essential oil dissolved
in a fatty
base oil. The large molecules of fatty vegetable oils are
not as
stable as the tiny ones that comprise essential oils. 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. We call this “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.
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, 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. 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. (See
section
on Heat at the beginning of this chapter for a more thorough
discussion on the effects of temperature on 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. To know if an oil blend contains
a fatty
carrier oil, read the label. If you want to extend their shelf
life,
refigerate 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. (More on
this
in the section on Heat earlier in this chapter.)
If anyone asks you about the shelf life of a
pure therapeutic grade
essential oil, just say, “5000 years at least.”
If they ask you about the shelf life of an oil
that has been expressed,
solvent extracted, or mixed with a fatty base, just say, “It
depends.”
___________________________________________________
NOTE: The article above is an extract from The Chemistry of
Essential Oils Made
Simple by David Stewart, Ph.D. The book will be 896 pages
long in
hardback and its price is $49.95 plus shipping.
Available from CARE at 800-758-6629
or via the internet at http://www.RaindropTraining.com
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THE RAINDROP MESSENGER
Official Newsletter of C.A.R.E.
The Center for Aromatherapy Research and Education
Rt. 4, Box 646, Marble Hill, Missouri USA 63764
(573) 238-4846
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IMPORTANT NOTE: The information in this newsletter
is not meant
to diagnose, prescribe, or substitute for professional medical
assistance. It is provided as information only for your better
understanding of holistic health. In case of medical need,
please
consult an appropriate licensed professional.
