Choosing a plant source...
some research. Go to the library. Better yet, go to a chem
library at university. The data for many essential oils are in
specialized chemistry books. You must do the research.
idea is to try distilling the essence of cumin seeds, but do this only
if you want the whole place to smell intensely like cumin for days
. It's hard to overstate the intensity of the odor. Even if
you love curry, you might lose all desire to eat curry for a while.
The aroma chemical is called cuminaldehyde. It's an oily liquid, p-isopropylbenzaldehyde. See Introduction to Organic Laboratory Techniques, 3rd Ed., by Pavia et al., 1988.
Extracting Essential Oils and Fragrances
Fig. 1. Syringa vulgaris, or common lilac, blooms for only a short time in late April or early May. It has a pleasant fragrance.
Different fragrances can have different degrees of stability to heat
and oxygen. Some will distill effectively; some won't.
CAUTION: You alone are responsible for safety.
Information is provided for educational purposes only. You assume ALL responsibility for consequences that may arise.
If you choose to attempt anything described
on this site, you do so entirely at your own risk. Please review
for this web site.
This article is subject to copyright. If you see it appear on
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Terminology / Definitions
Some Fragrances Won't Distill
Terminology / Definitions
- the long,
often corkscrew-shaped passage that recondenses the steam and
volatilized oils. It is one component of a distilling apparatus. Typically, a laboratory condenser has two side
tubulations. Water hoses are connected to these; one goes
to the faucet, the other to the drain. When the faucet is turned
on, cool water runs through the outer jacket of the condenser.
Distillate - the liquid that ends up in the receiving flask when the steam (etc.) turns back to liquid in the condenser.
Distilling flask - the
source vessel, containing the herb / spice and the water to be
heated. Technically, in chemistry the term "distilling flask" refers to a
round-bottomed flask with a long neck and a long side arm or tube.
Hydrosol - a colloidal dispersion of essential oil droplets in
water: in other words, an emulsion. An oil-water
dispersion may or may not separate by itself, depending on the
stability of the emulsion. Thus, the hydrosol is not necessarily
a by-product, but instead a crude product; here, it is simply the
the case where a distinct oil layer separates after standing, the term refers to
the watery liquid that remains behind. Some fragrance components are about as soluble in water as they are in
oil, meaning some will remain in the aqueous layer after spontaneous
separation of the oil layer. Again, the stability of the emulsion
plays a role here. Because the distillate will almost certainly contain polar
organic compounds, it's
likely that some
proportion of oil will remain permanently dispersed in the water
layer. This would be a more or less permanent hydrosol.
Maceration - an
carried out by crushing the plant material and soaking in liquid such
as water, glycerin, ethanol, or vegetable oil. This is
carried out well below boiling temperature; however, hot
liquids may be used to help break cell membranes and release the
components. There is not a precise definition in this
regard, since the word goes back at least to the 1400's.
is for fragrances that don't withstand steam distillation. The
chemically "fragile" fragrances tend to be more stable in colder
solubility also decreases. The best extraction seeks a balance
solubility and heat-stability; however, one way to offset the
problem is simply to soak materials for longer. Another is to use
a homogenator (laboratory blender) or high-powered ultrasound device to
Solute - the solid, liquid, or gas that is dissolved in the solvent. Salt can be a solute in water; CO2 can be a solute in water; fragrances can be solutes in alcohol; etc.
Solvent - the liquid that
does the dissolving. In the broadest sense, a solvent needn't
always be a liquid. Furthermore, in cases where multiple liquids
are involved, the line between "solute" and "solvent" isn't always
Source vessel - see
"distilling flask". In traditional distilling terminology, this is
often called the "distilling pot" or simply the "pot". However,
since various bad actors have so thoroughly corrupted the King's
English, the word "pot" has taken on a rather unfortunate
connotation having nothing to do with a container. Corruption of language is one of the devil's
Let us think back to inorganic chemistry. Supposing there were a
solution containing dissolved salt in water, and supposing that
solution were boiled, the dissolved salts would remain behind while the
water would evaporate. In other words, the solvent would
evaporate, while the solute would stay behind in the distilling
flask. Thus, the distillate would be pure water.
Recall now fractional distillation from organic chemistry. When
the solute is a liquid, such as alcohol, and the solvent is another
liquid, such as water, the components can be separated by virtue of
their different boiling points. As you may also recall, however,
certain liquids will form azeotropes
with water, or sometimes with each other. In practical terms,
that means the same composition will carry over into the receiving
flask. In other words, distilling such solutions will not
separate them unless we take special steps to "break" the
azeotrope. Obviously, we must accomplish this before or during
distillation, not afterward.
An alcohol-water mixture might begin to separate as desired, until we
arrived at some azeotropic ratio of alcohol to water. From that
point onward, the rest of the distillate would be identical in
composition to the liquid in the source flask.
You may recall that many essential oils and fragrances are steam-volatile. In other words, the steam carries with it appreciable amounts of the desired compound.
One can pass steam through a container full of plant material, but the
simplest way is to put the crushed plant material in water and boil
it. The steam will carry away steam-volatile components.
Earlier we discussed azeotropes. We can think of such
steam-volatile compounds as forming azeotropes as well.
There is no easy way to make the essential oil compounds come over
separately from the water.
One might think it possible to
attempt dry distillation of the plant matter, but there's a
problem with that. Many of the fragrant compounds (e.g.,
aldehydes) are susceptible to oxidation; the temperatures
involved in dry distillation would ruin these. In fact, the lack
of temperature control can easily lead to charring of the plant
distillation of plant matter can easily become pyrolysis,
entails permanent chemical changes that don't make very nice
fragrances. It's probably a better idea all-around to use steam.
One can simply put some of the crushed
herb in water and boil it. That is the most ancient
method. When the steam re-condenses, the resulting liquid
the distillate) will also contain the essential oil. This
oil may remain inseparable by mechanical means, or it may
partially separate on standing. Don't forget that essential
oil often represents only a tiny portion of the total weight of plant
matter. It may require a kilogram or more of starting material
just to end up with a couple milliliters of oil. The oil will not
separate in a recoverable manner if there simply isn't enough of it.
separation of an oil layer is less probable when the oil contains polar organic compounds such
aldehydes, ketones, alcohols, and carboxylic acids. Chances are that it
will! Some of these
are the fragrant compounds themselves; others are nuisance
components that do little else but hold the desired stuff in emulsion
water. Either way, one can achieve a purified essential oil only
by resorting to additional steps. In the organic chem lab (and
industrially), one would use a hydrophobic solvent. Small-scale work calls for a separatory funnel,
shaking some distillate together with a solvent such as methylene
(dichloromethane, CH2Cl2). The methylene
chloride layer, which
separates readily from the water layer, would contain the essential
The organic layer could be evaporated on a
slow steam bath in a fume cupboard. The less-volatile essential
oil would remain behind, while the dichloromethane would evaporate.
Any organic solvent that won't dissolve appreciably in water could, in
used for solvent extraction of the distillate. It is helpful to know the
partition coefficient of the desired
solute; that will be particular to the solvent system you're
planning to use. Someone, somewhere in the vast chemical
literature may have
found this coefficient already.... or not. Also, the choice and
grade of solvent
depends on what you're going to do with the oil. It is up to you
to know the appropriate solvent. We cannot recommend anything in
particular. Please consult the literature. Keep in mind
that industrial extractions often rely on solvents that wouldn't be
appropriate elsewhere. Industry has developed reliable ways to
remove solvents such as methanol (etc) that would otherwise present a
serious toxicity problem. That's why, at least traditionally,
many of the flavorings in use by the food industry have been extracted
with solvents that don't belong anywhere near your food. See for
example the Handbook of Solvent Extractions by Lo, Baird, and Hanson.
A few herbs and spices that lend themselves to steam distillation:
Caraway seeds contain d-carvone, a pungent ketone having a cyclohexene ring.
Cinnamon - if the small excess
of cinnamon in last year's batch of pickled watermelon rinds is any
indicator, cinnamon oil is hot stuff. Don't taste the distillate.
Cumin - source of cuminaldehyde... if you want the place to smell like "curry x 1,000".
Ginger - chop up some fresh ginger into tiny pieces and try distilling.
Lavender - a very popular choice for steam distillation
Lilac (Syringa vulgaris) - use the flowers. According to an article on Bojensen.netand
the diagrams there, the primary fragrance
components don't appear to have ester linkages. Something decent
should survive, perhaps being amenable to separation with a
column. Whether it will smell exactly like lilac is another
Orange - the citrus oils
are present mainly in the "zest" of a citrus fruit.
Peppermint - the smell is pungent ; according to legend, rats and mice will avoid the odor of peppermint.
Spearmint and Catnip are also in the mint family.
While we're on the subject: the concentrated oil of herbs and
spices is not necessarily edible. Peppermint oil is a good example (don't eat it!). When in doubt, don't taste
it. Do your research on this.
Take the time to set up your glassware properly.
This may require some minor construction. Plan it out carefully; do not
take shortcuts here. Stability of the setup is crucial. You
are expected to know how to achieve this properly. Following are
Because a Graham condenser has to be set up in the vertical position,
there will be a significant height difference between one side and the other (Figure 1).
distilling half of the setup will be much higher off the bench than
will the receiving half of the setup. A column (Vigreux, Hemple,
etc.) would make up for some of the height differential, but this would change
the composition of the distillate by fractionating one or more
components away from others. That may or may not be desirable,
depending on the fragrance(s) being sought.
||Figure 1. Temporary setup of the glassware, only to illustrate the height differential.
To set up the apparatus for actual use, build a sturdy riser or shelf to elevate the left-hand support stand.
A C140 or C150 support stand is too short by itself. Figure 1
shows an extra-tall stand (C160), but even this ought to have a 2- to 6-inch riser built beneath it.
base of a C140 would have to be elevated 10 to 12 inches off the bench.
Anchor all supports firmly!
It's possible to use a support stand mounted to a permanent riser or
shelf, such that ten inches (approx.) will be added to the effective
riser could be a block, a shelf, a stack of 2x8 sections (secured with
nails or bolts) or something of that nature. Don't use a
box. Don't use something fragile. Don't use anything that
could be knocked over easily.
The author in the past has
constructed various supports out of 2x4's, 2x8's, and so forth.
Even short legs should have diagonal supports to prevent racking.
If you don't
have good carpentry skills, find someone who does.
Alternatively, procure a 1/2" steel rod at least 26 to 30
inches tall. Build this upright rod permanently or
semi-permanently into your lab bench. Here, once again, you may
need to build some
kind of a riser to support your heat source; perhaps the upright
rod could pass through a hole in the riser.
The right-hand portion of the apparatus (according to Figure 1, above) can be held with a support stand and clamps; it should not require any special riser. This half of the
setup includes the Graham condenser and the receiving
flask. You may need two clamps to hold these
securely. Remember that a Graham condenser must be vertical to
work properly. Don't forget to anchor the base of your support
stand to the lab bench.
The end of your lab bench should have a sink for the condenser cooling
hoses. A laundry sink typically has a standard hose thread on the
outside. Obtain a hose barb (hardware store) and run some Tygon tubing from the
faucet to the upper tubulation of the Graham condenser. Run
another piece of Tygon tubing from the lower tubulation into the sink
drain. Make sure the cooling hoses will not come loose and spray
water on your hot glassware!
Using (e.g.) a Vigreux or Hemple column in the setup will take away much of
the height differential, but the Vigreux especially will alter the ratio of
products in the receiving flask. Such a column might be useful to try
separating the products later, especially if there are several fragrance components having different boiling point.
When distilling essential oils, do not let the source vessel evaporate to dryness. This can cause
charring of the plant material, which would ruin the product.
We have recommended on
our web site to use a sand bath for many heating purposes, but it's better to use a boiling water bath
or steam bath
for essential oil recovery. The flask containing
the herbs and the water is clamped in place so it's about an inch from
the bottom of a lightweight metal pot. That pot is then filled
with water. As the water in the metal pot boils, the
heat transfers to the distilling flask. This limits the
temperature in the distilling flask, ensuring that your herbs or spices
will not become charred.
The ancients would have been able to use some form of the water bath,
and it's likely they did. While you might simply try to make sure
the source vessel never runs dry, there's always the possibility of
isolated pockets of herb / spice / plant matter that remain dry.
If any of these be directly against the glass, they could
overheat. This could contaminate your fragrance with burnt
water bath eliminates this danger.
Some Fragrances Won't Distill
As mentioned earlier, it's
important to remember that certain fragrances cannot withstand
steam distillation. Jasmine, for example, contains benzyl
acetate, which is the ester of benzyl alcohol and acetic acid.
Depending on the size, shape, and type of molecule, the ester linkage
can be prone to hydrolysis. Benzyl acetate tends to
hydrolyze upon exposure to steam or boiling
water. Acidic or alkaline water will increase this
effect. The result of acidic hydrolysis will be benzyl alcohol
and acetic acid instead
of (or in solution with) the fragrant compound desired. Alkaline
conditions will yield the corresponding alkali acetate, plus benzyl
Usually, neither the alcohol nor the carboxylic acid smell anything
original ester. Sometimes the components of ester hydrolysis can
have a rancid odor. This also explains the unpleasant
transformation that seems to happen to the cheaper perfumes and
colognes. Many of these are ester-based, whereas the more
expensive ones tend to use aldehydes and ketones. The human body
generates 100 to 250 watts of heat during activity.
Carboxylic acids, released by bacterial action on human sweat, accelerate the hydrolysis of these cheap fragrances.
Note that certain plant esters will still
yield a fragrant product after distillation. Thanks to
steric hindrance and perhaps other factors, some esters are so
resistant to hydrolysis that they can be distilled without appreciable
change. Alternatively, the chemical characteristics of the ester
and its components may be such that usable ester is still able to come
over into the distillate..
Some fragrance compounds are quite sensitive to oxidation. They
remain intact in the living flower or plant, but they change to other
compounds when exposed to steam, boiling water, or hot air. One
may notice, for example, that the distinctive odor and flavor of cilantro does not withstand drying.
is one other factor to hinder recovery of certain fragrances:
some fragrant components may not be steam-volatile in the first
place. They would remain behind in the source vessel, bound to the original plant material.
For any of the above-mentioned reasons, there are some herbs and
spices that are no good for steam distillation. They must be
extracted directly with
organic solvents or with supercritical carbon dioxide, the latter being
generally out of reach of the small-scale operator. Once again,
your responsibility to find out what solvents are / aren't appropriate
for extracting oils. You must also be fully aware of any
potential toxicity or allergy considerations.
Outside of major industry, the solvent extraction
of essential oils for human use is normally done with vodka, neutral
grain spirits (C2H5OH
with about 5% water) and/or vegetable glycerin. Obviously,
denatured alcohol and rubbing alcohol are out of the question.
Many materials will extract into vegetable oil, especially with extended soaking in a warm place.
Methyl benzoate is a fragrant ester present in certain plants, including snapdragons.
It also happens to be the odor that alerts a specially-trained canine
to the presence of a certain very popular but non legal alkaloid that
tends to come from South America . According to Dudareva et al., methyl benzoate is "the most abundant scent compound detected in the majority of snapdragon varieties" . Another paper notes that methyl benzoate is present in Stephanotis floribunda ,
also known as Waxflower, Madagascar Jasmine, and Hawaiian Wedding
Flower. Although various submerged agendas tend to undermine Wikipedia's
reliability in certain areas, it's probably safe to believe Wikipedia's
claim that S. floribunda is popular in wedding bouquets .
We have not tested whether snapdragons (etc) will actually cause a false
positive with a canine; however, the potential is
obviously there. Indeed, canines have falsely alerted to perfumes and other innocuous objects (as in the case Horton v. Goose Creek Independent School District) . Methyl benzoate is still methyl benzoate, no matter where it's found. If the bulk flowers yield
no hits, it would be interesting to test various extracts of the flowers (e.g., EtOH tincture; glycerin extract; chilled aqueous homogenate; etc.).
Perhaps the cast of Mythbusters
would be willing to treat themselves and their luggage with snapdragon
extracts and submit to a canine test. Just to keep it objective and
interesting, let's see if they can get through a Peruvian airport
staffed by strangers who don't know it's a test. No
This writer is aware that competent scientists in LE are working on the problem of false positives. In
the meantime, though, it is of some concern that glassware having the
scent of (e.g.)
might be hard to explain to someone who lacks familiarity with natural
fragrances and yet is in the position of possibly hauling someone away
based on a canine sniff. While we certainly support the
apprehension of the bad elements in our society, we are also for the
protection of the innocent. Working with fragrances and essential
oils is a legitimate, wholesome pursuit enjoyed by many
We need to start reversing the trend toward a society in which the only
safe thing to do
is shuffle papers, watch TV, and do what everyone else does.
Otherwise, we're going to be in bad shape. Our greatest inventions were
discovered under circumstances that probably wouldn't even be permitted
today; consider the stories of Thomas Edison, William
Perkin, and Charles Hall, to name just a few. The outcome of building a society stacked against innovation and
independent inquiry is to become marginalized, at best. If America doesn't do
something to right her course, the prospects are a disaster.
Finally, whatever you do, stay away from those plants that are proscribed by law. It is up to you to find
out which ones are off limits, and to comply with regulations. Stick
with herbs and spices you can buy at the grocery store or from some other reputable source, and there
shouldn't be any concern.
Wear your safety goggles, stay safe, and have fun.
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CR Scientific Catalog
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. Waggoner P, Johnston J, Williams M, Jackson J, Jones M, Boussom T,
Petrousky J. "Canine Olfactory Sensitivity...". Proceedings of SPIE 2937:216 (1997).
. Dudareva N, Murfitt L, Mann C, Gorenstein N,
Kolosova N, Kish C, Bonham C, Wood K. "Developmental Regulation
of Methyl Benzoate Biosynthesis and Emission in Snapdragon
Flowers". Plant Cell 12 :949-961 ( 2000).
. Chen F, Effmert U, Hippauf F,
Kiefer I, Noel J, Pichersky E, Piechulla B, Pott M, Ross J,
Saschenbrecker S, Slusarenko A. "Biochemical and Structural
Characterization of Benzenoid Carboxyl Methyltransferases Involved in
Floral Scent Production in Stephanotis floribunda and Nicotiana
suaveolens". Plant Physiology 135:1946-1955 (2004).
. Lunney, Leslie A. "Has the
Fourth Amendment Gone to the Dogs? Unreasonable Expansion of
Canine Sniff Doctrine to Include Sniffs of the Home". September
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