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"essential oils are the volatile materials derived by a physical process from odorous plant material of a single botanical form and species with which it agrees in name and odor."
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• not all oils are essential oils
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the above is a good definition of essential oils but there is room for confusion. |
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correct usage -- "essential oils" should only really be applied to: |
| • | distilled oils, as the process of distillation by water and/or steam ensures that only volatile components are collected. |
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however, the term is also used correctly: |
| • | for oils expressed from the peels of citrus fruits, |
| • | and oils produced
by dry or destructive distillation where tar like materials are obtained
by dry heating in the absence of air or in a vacuum. birch tar oil
(rectified by steam distillation), copaiba oil |
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incorrect usage -- it is common now in aromatherapy
circles to incorrectly refer to other aromatic materials as essential
oils such as the following extracts: (in the list below, the extracts
and oils contain substantial amounts of non-volatile substances.) |
| • | balsams - natural exudations from plants e.g. benzoin, peru and tolu |
| • | resinoids - extracted from a gum or resin by solvents |
| • | concretes - hydrocarbon extractions of plant materials containing waxes and color in addition to odorous components |
| • | absolutes - alcohol extractions of the concrete |
| • | animal extracts - absolutes or alcoholic tinctures of animal excretions or glands and |
| • | fixed oils - non volatile oils such as pressed from seeds and fruits - "carrier oils" |
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• expressions
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expression is the physical process of squeezing the oil out of the plant material.
for essential oil purposes, this process is only used for citrus oils
where the oil is held in small sacs on the surface of the outer peel.
other oils produced by expression such as nut and vegetable oils are
known as fixed oils as they are not volatile. these fixed oils such as,
sweet almond, grape seed, peach kernel, olive and peanut oils, etc. are
basically odourless and used as carrier oils, massage oils or even for
food use.
the term essential oils is extended to citrus oils as their constituents
are mainly volatile, so volatile that they are regarded as top note
ingredients and for shipping purposes are regarded as flammable
("dangerous goods"). |
• sponge pressing
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original method |
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original process for the production of citrus essential oils was to cut
the fruits into 2 halves, the fruit being scooped out and the hollow
peels soaked in warm water. the thick inner pith absorbs water so
swelling it plus making it resistant to cracking. the peels were then
pressed against a small sponge one by one turning them inside out as
they are pressed. the thickened and swollen piths thus apply pressure on
the oil sacs rupturing them. the oil leaks or squirts out of the
ruptured cells and is absorbed onto the sponge. the sponge is then
squeezed out into a collecting bucket.
this method is labour intensive and although not widely used it is
apparently still used for the finest sicilian lemon oil. modern
mechanical methods have been designed to reproduce sponge pressing but
maybe the oil produced is not quite as good as the purist demands. |
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ecuelle a picquer method |
| the second method was to place the whole fruits into an
inverted bell shaped container, lined with rows of spikes. as the
fruits were turned in the container the spikes rasped the oil sacs in
the outer peel of the fruits releasing the oil. the oil trickled down
the inside walls of the container and collected in the bottom.
periodically the bottom was opened to allow the oil and peel debris to
flow out. there are larger versions of this process designed for more
commercial production. |
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juice by product |
| a third method comes under citrus fruit juice
production rather than essential oil production. this is where the whole
fruit is processed to produce the fruit and the oil is an unwanted by
product that is separated and collected for sale. in terms of quantity
this is by far the most important source of cheap oils such as brazilian
sweet orange oil. |
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• absolutes and concretes
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solvent extraction |
| solvent
extraction provides a means of obtaining a higher volatile yield from
the plant or, in some cases, a product that cannot be obtained by other
extraction processes, (e.g. jasmine or carnation), with the potential
current exception of supercritical co2 extraction which remains, in many
cases, a very expensive process.
an extracting container ("still") is loaded with perforated trays of
blossoms or plant material to be extracted. the blossoms are steeped in
the solvent, (usually a hydrocarbon such as hexane), which is circulated
through the material washing the oil from deep within the plant cells.
the solvent dissolves all extractable matter from the plant, which
includes non-aromatic waxes, pigments and volatile aromatic molecules.
the solution containing both solvent and dissolvable waxes and color
material is filtered and the filtrate subjected to low-pressure
distillation using a vacuum pump to recover the solvent for further use.
the remaining waxy mass is what is known as the "concrete" which in the
case of jasmine may contain as much as 50% of the volatile oil
components.
the concentrated concrete may be used in perfumery but its use is
limited as the waxes present are insoluble in alcohol (ethanol) the
normal solvent for finished perfumes and colognes. it is also generally
too expensive for commercial use in soaps and cosmetics. the concrete
may be stored as it is more stable in this form than as an absolute,
which will be prepared as needed.
to prepare the absolute, the waxy concrete is gently warmed and stirred
with ethanol. during the heating and stirring process the concrete
breaks up into minute globules. since the volatile oil components are
soluble in alcohol and the waxes are not, an efficient separation of the
two takes place. remaining traces of concrete are removed by chilling
the solution to very low temperatures (around -30° f) precipitating
remaining waxes. the solution is then cold filtered leaving a wax-free
solution of the absolute, color and alcohol. the spent waxes from the
concrete minus the absolute may find use in soap perfumery or a
general-purpose wax for candles and cosmetics where the remaining soft
odor may be useful. |
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carbon dioxide (co2) extraction |
| extraction with carbon dioxide is a relatively new
process that has been hailed as a major breakthrough for the essential
oil industry. co2-distilled oils are superior to steam distillates
because of their fresh and typical flavor and aroma which are very close
to the botanical raw material.
what is meant by hypercritical? -- this is a term commonly used in conjunction with co2 extraction.
any substance can exist in three different states: gas, liquid and
solid, depending on its temperature and pressure. in addition, certain
substances can be found in the hypercritical state. they are neither
liquid nor gas, but rather they are both. the hypercritical fluids
disperse as readily as gases and also have solvent properties. carbon
dioxide normally only occurs as solid dry ice or a gas, however when
subjected to special conditions under high pressure, the gas turns into
liquid. this liquid co2 can be used as a very inert, safe "liquid
solvent."
carbon dioxide becomes hypercritical at 33°c. hypercritical carbon
dioxide then becomes an excellent solvent of essential oils, in an
extraction process similar to that used to extract absolutes. the
advantage is that the whole operation takes place at a low temperature
and, therefore, the essential oil is not affected by heat, as may occur
in the distillation process.
- advantage(s):
- the extraction process is almost
instantaneous and because the solvent is virtually inert, there are no
chemical reactions between the solvent and the aromatic substances.
- with this method, more top notes,
fewer terpenes, a higher proportion of esters, plus larger molecules,
are obtained. the resulting oil contains very little color matter and is
said to be more like the essential oil in the living plant. (the
normal distillation process seems to form many terpenes and also breaks
down some of the acetates (esters) in the plant material.)
- no solvent residue remains, since
at normal pressure and temperature, the co2 simply reverts to a gas and
evaporates. being an odorless normal component of the atmosphere, it is
non-polluting and is non-flammable.
- disadvantage:
- co2 extracted oils may cost up to 10
times as much as the steam distilled oils or absolutes. if not for the
price disadvantage these materials almost certainly by now would have
become the preferred extracts. the price is largely governed by the
expensive equipment needed to control the conditions required to keep
the co2 as a hypercritical liquid.
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alcohol extraction |
| some trees' resins such as benzoin, frankincense and
myrrh may be extracted with alcohol directly to produce a resinoid.
these resinoids can be so thick, effectively "rock-hard" solids that
they require materials such as benzyl benzoate or diethyl phthalate to
be used during the extraction process to "plasticize" them. when the
alcohol has been removed under vacuum, the non-volatile plasticzers
remain with the extract. note that very few commercial resinoids on the
market will have no added plasticizer. |
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totals |
| what is meant by "totals"; "select" or "selectives"? what is the difference:
selects - low pressure is used for this method and the resultant
product will not have been affected by extreme temperature changes.
selects are easier to work with than totals, but do not contain all the
soluble components like totals do. selects contain mainly volatiles and
essential oils and are superior to steam distillates.
totals - higher pressure is used for this method and the
resultant product contains all of the soluble components like those
found in the herb. totals are more complete products, although they're
thicker and slightly harder with which to work. it's recommended that
you warm the total by submerging the container in hot water and letting
it liquefy or the total may be added to a small amount of carrier oil
with a long shelf life (such as jojoba or fractionated coconut oil) and
stirred until it's well blended. |
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• are your oils genuine
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you may hear answers from suppliers like -
guaranteed 100% natural etc. he may be telling the truth. he may blind
you with science and send you a gas chromatogram - as much use as a kiss
'o gram except to the chemist that produced it. the most basic tools
that you need to reassure yourself that oils are genuine come from your
own observation and logical reasoning. |
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first: the supplier (note none of these may be negative factors but each answer builds a picture of reliability.) |
| • | are they the producer or merely a trader or broker of oils? |
| • | are they represented local to the production area? |
| • | what sort of checks on the oils do they carry out? |
| • | do they have a laboratory? |
| • | how much experience do they have? |
| • | what is their ethical stand? |
| • | do they supply mainly to perfumery companies, flavor companies or aromatherapists? |
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| | case example: |
| | when enquiring of a seller [who
supplies mainly for aromatherapy outlets] about his supply of lavender,
his first question was - "how much do you want to pay?" |
| | reading between the lines he could supply: |
| | | • | the genuine unadulterated lavender oil, |
| | | • | a lower grade of lavender oil, |
| | | • | semi-genuine,
natural but from different species (blends of lavender, lavandin, spike
lavender, rosemary, eucalytus, mentha citrata, clary sage etc.), or |
| | | • | largely synthetic (blends of linalool and linalyl acetate and traces of oils). |
| | the choice was mine. |
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second: the price - is it consistent with a genuine oil? |
| • | what country does the material come from; is labour there cheap? |
| • | oils from europe will be generally more expensive than those from asia. |
| • | think about the area of land required to grow the crop of natural product. |
| • | citrus
oils: the oil is visible in the skin of the fruit - many fruits to a
tree; many trees to an orchard - probably not expensive unless a rare
fruit. |
| • | grass: dense growth; big leaf area; easy to collect - leaf has strong smell so probably a lot of oil - oil probably cheap. |
| • | herb: use flowering tops of herbs - grows densely - doesn't have a lot of flowers so probably more expensive. |
| • | flowers: use petals which are very light and generally have a low oil content so probably expensive. |
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| | case example: |
| | a supplier received an inquiry for
a number of oils, one of which was neroli oil. he said he could supply
it but warned that it was expensive. he would check the current price
and quote, but to expect it to be in the ball park of $2,000/kg. a
few days later the customer placed an order for most of the oils. noting
the neroli being absent from the list, the supplier inquired. the
customer replied, "oh never mind, i found a supplier in india that
sells genuine neroli oil for $100/kg." |
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third: the physical appearance - does it look consistent with descriptions that you have read from information sources? |
| • | most essential oils are light coloured but very few are completely colorless. |
| • | is it the right viscosity? |
| • | if it's an absolute, is it dark enough and viscous enough? |
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fourth: the smell - if you don't know the raw plant material check out the descriptions in books. |
| • | does it smell right? - smell it on the top, middle and bottom note. |
| • | does it last too long on the smelling strip? - synthetics may have musks added. |
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caveat emptor* - the buyer will often deliberately hide behind
the supplier's assertion that it is natural. the supplier may be hiding
behind his supplier's assertion that it is natural. it is usually easier
to accept the guarantees, cheap prices and abdicate responsibility
rather than have to think, so...*let the buyer beware! |
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• are your oils fresh
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it's difficult to know when we buy essential
oils or aroma chemicals whether they are fresh or past their best
without specific experience with those materials. unfortunately oils
don't usually come in sealed packages with "use by" dates. we can of
course read up on them but that is not quite the same. |
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there are a few rules of thumb that can help you gauge an oil's freshness. |
| • | first check your
source. are you buying from the manufacturer or a dealer. if a dealer
does he appear to have a regular turnover? are essential oils his main
business? |
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| • | essential oils and
absolutes should have representative smells of the original plant
material. generally the more like the original leaves, herbs or flowers,
the more likely it is to be fresh. |
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| • | citrus oils -
citrus oils when they are first pressed have a definite light color of
the fruit they came from. i.e.. lemon oil is yellow, orange oil is
orange, tangerine oil is tangerine, bergamot is green etc. the colors in
the citrus oils are generally not very stable. if the oils have been
exposed to light or kept in poor storage conditions their color fades.
so most citrus oils after a year or so tend to become almost colorless.
note distilled lime oil is colorless even fresh because the color does
not volatilize with the oil during the process of distillation. |
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| • | terpenes (that
occur in all essential oils) tend to polymerize in the presence of
oxygen and produce sticky resinous masses so look for any signs of gooey
masses, they will be translucent brown and will tend to collect around
caps or may present themselves as sticky precipitates. |
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| • | if an oil is very
freshly distilled it will have a gassy green "still" note on top. this
is particularly characteristic on geranium oil which should have a sweet
corn note (dimethyl sulphide). these notes generally dissipate after a
month or so. on many oils these "still" notes can be unpleasant so don't
be too quick to dismiss an oil that is guaranteed freshly distilled. |
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| • | woody type oils
with high concentrations of sesquiterpenes (or sesquiterpenoids) are
more viscous than their mono terpenoid cousins and become increasingly
viscous with age. this frequently improves the odor of the oil. such as
in patchouli, vetiver, sandalwood etc. |
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| • | some oils kept in
steel drums (even lacquered ones have scratches and allow some contact
with bare metal) will pick up iron (fe) from the steel material and this
slowly darkens the oil over time. the most susceptible oils are the
spicy oils clove and cinnamon which will eventually turn black but many
oils and materials will be affected. |
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| • | most oils will
tend to soften in odor as they age as the functional groups (aldehydes,
alcohols, esters etc.) on the constituent chemicals break down. strong
aldehydes turn into their weaker smelling alcohols. if esters break down
they may produce the acids and a sourness may develop. |
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of course these tips will have many exceptions but
these generalities should help you to pick out most common changes in
oils that could indicate they are past their best. they are a good
starting point to add your own experience with specific oils. |
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