Amateur Aromatherapy

Distillation of Essential Oils

I know you don't want to here this but steam distillation of essential oils is not really the territory of 'amateur' aromatherapists. Although I get a lot of people asking me how to do it, I have never heard from anybody who has successfully extracted more than a pin-sized drop of essential oil at home. Perhaps they did not stay alive long enough after the boiler exploded to e-mail me with the details. You can forget holistic therapy as you will need some basic science, chemistry and some practical knowledge of the fractional distillation process. Despite this, I'm sure you would be interested in reading about it. As I don't work in the industry I have cobbled this page together from references across the Web with some smart-arse comments from me. So don't ask me technical questions as I will not be able to answer them! I have included some appropriate acknowledgements at the end.

"Distillation represents a dynamic part of a whole process where the ethereal oils contained within a plants aromatic sacs or glands are liberated through heat and pressure and transformed into a liquid essence of sublime beauty. In a plants journey from seed to maturity, a constant natural process of distillation is occurring as it draws into itself elements from the surrounding environment and converts them into the substances that give it life, structure, texture, color and fragrance. Harvesting the plant at the appropriate time and endeavoring to distill from it the miracle of its essence, is the high art and craft of the distiller."

Sounds good but how do we do it ?

"When considering the beauty and mystery of the world of aromatic plants and their precious essences which are distilled and extracted by various methods, one comes to realize that in the short space of a lifetime one may only scratch the surface in understanding the subject. As all of you know the process of growing any crop requires a lot of skill and knowledge on the part of those engaged in such work. Working with nature over a period of many years ingrains in one a respect for the wonders around one and develops a sincere humility as learns to adjust to the environmental changes that influence the growth of a plant from seed to maturity. When plants have reached the moment of perfect aromatic maturity, they then go into the hands of those engaged in distilling or extracting their precious essence. It is one more vital part in the entire process. It is a subject that has its own aura of mystery. Actually little has been written about the intricacies of the subject and certainly one must be directly engaged in this process to really understand it. The creative imagination will have to serve for those of us who have not yet been afforded this opportunity."

Oh get on with it.

"First of all each and every aromatic raw material has to be considered as an individual entity. The perfect time for harvest of some plants is more straightforward than others. Flowers such as Rosa damascena, Jasminum sambac, Jasminum grandiflorum, Citrus aurantium var.amara (Neroli), must be plucked just as their buds are beginning to unfurl and at a very specific time of day in order to capture the pure essences and produce oils or absolutes of the highest quality. Once a flower has passed its prime (which in most cases happens within a day or two) the essential oil quality degrades quickly. Even in this case, there are some interesting facts to consider. Some flowers have a bloom season of a month or less (Rosa damascena) others can be as long as 6 months (Jasmin sambac) Whether the season be long or short, there are some days within that period where the the flowers have a balance of constituents which are considered the most refined and perfect of all. But there are many plants where this is not so. Consider the grasses like Lemongrass, Palmarosa Citronella, and Gingergrass. The balance of their constituents changes from day to day as they pass from mature grass to seed. Many times a specific balance is required by large consumers of the oil and so test distillations are done from day to day with immediate gc analysis being done to see what that balance is. This is particularly true when particular components are being isolated for for the flavor and fragrance industry. But one should not think there is only one profile for a particular oil. There are often many different profiles depending on not only the stage of maturity of the plant, but the soil it is being grown in, the method of distillation, the length of time between harvest and distillation, etc."

Sounds complicated. Maybe I'll just buy the oil rather than grow it myself. 

"In examining this subject we also have to consider that in many countries, a particular crop is not being grown by just one person on a specific piece of land. Often there are large numbers of farmers growing the crop on small land holdings. There may be a variety of cultural practices employed by each that will influence the health and vigor of the plants. Certainly the aromatic raw material will fit into certain parameters, but it is important to realize that plants are greatly influenced by the environment in which they live and even small differences in micro climate, water, soil etc have their effect. Very few farmers have their own distilleries and often the material growing in a certain local is taken to a central facility where the material is distilled.

Prior to distillation the distiller may also be presented with the problem of how to properly disintegrate or reduce in size (called comminution) the material especially if he is dealing with dried aromatics like spices, seeds, roots, etc. These materials have to be reduced in size so that during the distillation process the maximum surface area of the plant material comes in contact with the distilling/extracting medium (generally water, steam, solvents, CO2) and release the volatile oils contained in the plants oil glands or sacks. It is important that this be done in such a way that the comminution process itself does not destroy the volatile oils (due to excessive heat in grinding, crushing or slicing) or that their is not to much lag time between the time when the plants are thus prepared and then distilled (as when the aromatic materials are crushed,etc much evaporation of natural oil can occur in a brief time). The ideal therefore is to effectively and carefully reduce the size of the aromatic plant materials so that the steam, boiling water can vaporize the maximum amount of essential oil."

Sounds tricky as well.

"The cell walls of some plants are very thin and permeable which allows steam, boiling water, solvents, etc to easily penetrate them, and carry away the essential oil contained in the oil sacks or glands. But others have to be carefully prepared before their essential oils can be released. Seeds need to be thoroughly crushed and roots, stalks and woody material need to be chopped into fine pieces. A whole range of comminution equipment has developed to insure that this process is done in the most efficient and sensitive manner. Some companies have even evolved crushing equipment that disintegrates the material at sub freezing temperatures. The main thing is that as soon as the crushing or grinding has occurred, the distillation process should begin as the volatile oils rapidly evaporate into the surrounding atmosphere.

 Storage of plant materials prior to distillation is of importance to the distiller. Many plant materials (dried roots, seeds, woods) can be effectively kept for several months without significant loss of essential oil content provided the room is cool, dark, dry and free from air circulation. If these conditions are not meant then precious oil content can be lost due to oxidation and resinification. Some plants like peppermint and clary sage are sometimes partially dried before distillation as their very high water content makes it difficult to distill in the fresh state. It was once thought that there was little or no essential loss because of drying. But in fact this has been proved wrong. There is a loss of essential oil in general and specific components in particular. A detailed analysis of oil distilled from fresh peppermint and partially dried peppermint will reveal a host of differences especially in the minor and trace components. It does not mean that the oil from partially dried material is not beautiful, it just means that it is different."

Can an oil be beautiful ? 

"Then of course there are the issues surrounding the type of equipment to be used. Glass, aluminum, iron, stainless steel, and copper are all common materials used in constructing stills of different sizes and shapes. The still body itself (that is the vessel into which the raw material is placed) can be designed to hold water, to have steam pumped into it, have perforated plates upon which the materials sit, have automatic or manually operated stirrers to prevent materials from sinking to the bottom of the still and thus getting charred, etc.

Regarding distillation issues, some people say that glass is best, others copper, others stainless steel, etc. It is an interesting debate because those who follow a particular system have often attained high expertise in what they are doing and the type of knowledge they have acquired and the feeling for their equipment also greatly influences the quality of the end product. It is true that the majority of oils are distilled with a more commercial angle of vision. Large stills are created with efficient condensers, etc and many mechanical controls are put in place to be sure that the oils fit with the parameters of the international fragrance and flavor industry (which produces the majority of the oils that are sold today). But there are a growing number of small distillers who take great pride in their art and craft and are constantly refining their techniques of distillation so that the oils possess the greatest spectrum of aromatic molecules as possible. In saying this I do not mean to say that the large distilleries are devoid of such expertise. What they have accomplished in terms of providing beautiful oils is no small achievement, but there is also much to be said for the artisan working with their unit of 25-200 liters distilling oils of superior quality. I think we shall see more and more of these intimate endeavors arise in years to come."

Let's hope so but I don't want to pay a lot of money for a tiny bottle.

"Then when one gets into the world of the distillation itself, one has to possess a tremendous amount of knowledge about the specific plants with which one is dealing. One, either through intuitive knowledge or scientific training has to understand the incredibly complex aromatic configuration of the plant they are dealing with. Each plant possesses a range of aromatic molecules from low boiling to high boiling constituents. The art and craft of producing a truly amazing oil lies in understanding how to "tweak" ones distilling techniques so that the the process captures both the sublime top notes and the deep base notes. One has to know how to bring up the heat in such a way that the material begins to release its ethereal oil thus capturing the widest spectrum of molecules. This is where the high art and craft of distilling takes on its most sublime form and a person engaged in such aromatic creation happily devotes and entire lifetime to perfecting their technique. For each and every raw material that enters their still, they are having to discover the best method for distillation. Indeed, one might say that few are the noses that appreciate the nuances that they capture in their liquid gems. Most of us are acquainted with very fine oils that are produced in commercial stills but occasionally one comes across an artisan working on a more intimate level and their oils may have a particular charging and beauty that cannot be explained by any sophisticated mechanical analysis."

More craft than science ?

"In making an effort to appreciate the distillers art and craft one comes cross a number of terms that require some effort to understand. Methods of distillation include steam, water (sometimes called hydrodistillation), water-steam, and hydrodiffusion. Extraction techniques include solvent and CO2.

There are many technical terms which pertain to the operation of distillation-vapour pressure, thermodynamics, boiling point, atmospheric pressure, latent heat, hydrolysis, resinification, saturated steam, superheated steam etc. Each term has a world of research behind it and deserves careful study. It is beyond the scope of this modest introduction to the subject to go into all the exact details. All that can be presented here is a broad overview which is meant to instill in the heart a recognition of some of the intricacies of the subject (and hence the wonder and beauty inherent in it)"

Let's get started then.

"What does need to be understood about distillation though is that whether one is doing water, water-steam, or pure steam distillation one is going to be applying heat and pressure upon the aromatic tissues of the plant and by the very nature of this exercise certain effects are produced that are going to change the chemical nature of the essential oil as it exists in the plant. The processes of diffusion, hydrolysis and thermal decomposition do act upon the aromatic material during distillation producing an oil which has some similarities and some differences from the original. An essential oil should not be understood as something perfectly representing the oil as it exists in the plant. It is what it is, a new beautiful aromatic essence which arises as a result of many factors: environment, individual plant characteristics, care and nurturing of the farmer (watering, weeding, fertilizing, time of harvesting), proper comminution of the material prior to distillation, distillation technique, the understanding and awareness of the distiller, etc. In its highest form it is like a great work of art which captures something of the exquisite beauty of the living aromatic plant but is not the plant itself. It is an act of creation arising from a long set of natural processes into which the human element enters through taking a gift of nature and transmuting into a sublime treasure which can be transported in a small vial to any place. When the vial is opened releasing the trapped precious volatile vapors, the effect it has is as powerful as the creative imagination of the person inhaling it and the many processes that produced it.

From a simple outer standpoint-one can gain a comparative analysis of the different systems of distillation (water, water and steam, and steam distillation) by studying Book 1 of Ernest Guenther's 6 volume set called, Essential Oils. In presenting his finding one has to take into account as mentioned before, people that have developed an intimate knowledge of their distillation technique may have risen above such observations as Guenther makes."

Great. So now I need to buy a book.

These abbreviations will be used...

Types of Still

WD - Simple, low priced, portable stills; easily installed in producing regions

W/SD - Somewhat more complicated and higher priced than WD. The smaller type is also movable and may be installed in the field

SD - If well constructed, usually more solid and durable than than WD and W/SD. Possibility of large size for large scale distillation

 

Types of Plant Material

WD - Most advantageous for certain materials, especially when finely powdered; also for flowers which easily lump with direct steam. Not well adapted for materials containing saponifiable, water soluble or high boiling constituents.

W/S -Well Suited for herb and leaf material

SD - Suited for any charge except finely powdered material through which the steam forms channels ("rat holes"). Especially well suited for seed, root, and wood materials containing high boiling oils.

Modes of Comminution

WD - Best results with finely powdered materials

W/SD - Plant material must be uniformly but not too finely comminuted. Granulation gives best results with seeds and roots

SD - Same as above

Modes of Charging

WD - Material must completely covered by water

W/SD - Material must be evenly charged into the still

SD - Similar to above. Proper charging is very important; otherwise the steam channels through the plant materials and low yield results

Diffusion Conditions

WD - Good, if material is properly charged and moves freely in the boiling water

W/SD - Good

SD - Good if steam is slightly wet. Distillation with superheated steam or high pressure stem dries out the plant material, prevents diffusion, and causes a low yield of oil. Such distillation must, therefore, be followed by wet steam.

Steam Pressure Within the Still

WD - Usually about atmospheric

W/SD - Usually about atmospheric

SD - Can be modified (high or low pressure steam) according to the plant materials

Temperature within the Still

WD - About 100 degrees Celsius. Care must be exercised not to "burn" the plant material by contact with overheated still walls. Vaporized water be continuously replaced

W/SD - About 100 degrees

SD - Can be modified (saturated or superheated steam) according to the material.

Dry Steam - Steam that does not contain any unevaporated water. "Dry, Saturated Steam", is dry and also at the boiling temperature.

Wet Steam - Steam that contains unevaporated water as a mist in the steam vapor.

Saturated Steam - Steam which is at the same temperature as the boiling point of water at that pressure.

Superheated Steam - Steam which is at a temperature above the temperature of boiling water at that pressure. Therefore, Superheated Steam is always Dry Steam

Hydrolysis of Oil Constituents

WD - Conditions usually unfavorable. High rate of ester hydrolysis.

W/SD - Hydrolysis fairly low, provided no excessive wetting of the plant charge within the still takes place.

SD - Conditions good, hydrolysis usually slight.

Guenther - "Hydrolysis in our case can be defined as a chemical reaction between water and certain constituents of essential oils. These natural products consist partly, and in some instances largely of esters, which are compounds of organic acids and alcohols. In the presence of water, particularly at elevated temperatures, the esters tend to react with the water to from the parent acids and alcohols."

Conditions within the Plant Charge

WD - Good if plant material is covered with water and moves freely in it

W/S - Good if material is properly comminuted and charged. Prolonged distillation causes excessive wetting by steam condensation and lumping of the charges. Stills should be well insulated

SD - Conditions good, if plant material is properly charged,. Prolonged distillation with wet steam causes excessive steam condensation with the still and lumping of the charge

Rate of Distillation

WD - Relatively low

W/SD - Fairly good

SD - High

Yield of Oil

WD - In most cases relatively low, due to hydrolysis, also because water soluble and high boiling oil constituents are retained by residual water in the still

W/SD - Good, if no excessive wetting and lumping of the plant charge occurs. This would prevent steam from penetrating the charge thoroughly and result in abnormally low oil yield

SD - Good if plant material is properly comminuted, evenly charged, and distillation properly conducted. Lumping of the charge or steam channeling might cause abnormally low yield of oil

Quality of Oil

WD - Depends upon careful operation; "burning' of plant charge must be avoided, especially when distilling with direct fire

W/SD - Usually good

SD - Good if operation properly conducted all around

Distillation Water

WD - Distillation water in some cases must be redistilled, or more conveniently returned into the still during distillation (cohobation). Distillation waters contain products of hydrolysis, chiefly

W/SD - If properly separated the distillation water can be discarded in many cases

SD - Similar to above

Steam Boiler 

The steam boiler is in most cases an oil or gas fired package boiler. Biomass fired boilers are used in the Texas cedarwood oil industry, but also quite common in remote third world areas. There however, some distilleries purchase wood as a cheap local fuel, or burn fuel oil, while the spent biomass of the process is discarded, primarily for being too wet.

Stills

Stills come in all sizes, shapes and materials of construction. A still is basically a tank with some means of injecting steam at the bottom of the tank in a way that allows its uniform distribution, such as perforated crosses or plates, false bottoms, manifolds etc. This method is known as "hydrodiffusion", as opposed to "hydrodistillation". In the latter, the still is filled with the material submersed in water, and the oil is "boiled" out of the aromatic raw material. A comparison of both processes was recently described in a P & P article by M.H. Bolens. The opening of the still can be a simple manhole cover or a full size lid with the same diameter as the tank, depending on the unloading method. The steam/oil vapors exit at the upper aids of the still or through an opening in the lid, which is sometimes fitted with a coarse filter. Most stills operate at atmospheric pressure, some are designed to stand higher pressures, in the 2 bar range. The most popular unloading method is the basket-type (vetivert, Haiti), some of which have several cross-sectional trays (flowers, France). Stills that operate under pressure are sometimes unloaded under pressure through a large opening at the end of a cone-shaped bottom (cedarwood, Texas). Materials that require frequent loading and unloading are processed in stills mounted on pivots which allow to swivel the still into the upside down position and dump the entire content (lemongrass, Guatemala). Some stills are mounted on dump trucks and taken to the field for loading and unloading (mints, U.S.). Some stills are loaded and processed directly in the fields by hydrodistillation (wild herbs, Morocco).

Condensers

Condensers are of various types. From truck radiators to copper coils; shall and tube heat exchangers; pipes submersed in river fed canals; air cooled condensers; tube condensers inside sprinkler towers, etc., depending on the location, climate, available space and resources.

Oil Separators

The oil separator is the one component which is the most critical to the overall product recovery and profitability of the plant, whether conventional or continuous. Except in modern facilities, the separator often seems to get the least engineering attention from distillery operators in the field. The separator too, comes in a wide range of homemade designs, although the main idea is that of a continuous decanter sometimes referred to as a Florentine flask. Its efficiency is governed by a number of well known variables; oil and water specific gravity differential at various temperatures; phase viscosities versus ascending and descending cross-sectional velocity at various distillate flow rates and tank diameters; coalescing effects of different packing materials; emulsification effects; oil solubility at various temperatures; chemical composition and polarity of the oil and its effect on solubility, etc. Distillers of heavy oils, such as vetivert, are usually much more aware of the efficiency requirements of the separator than the distillers of light oils such as citrus oils need to be.

Example of How To Operate a Home Still

 

Remember that at all times you will be dealing with the hot metal of the retort and bird's beak. BE CAREFUL! It is advisable to wear gloves and eye protection when operating your distiller.

  1.  Make certain valves for sight glass are in the open position. Turn counter clockwise.
  2.  Make certain the clean out valve is closed. (Perpendicular )
  3.  Plug for water inlet should be in place, at least hand tight.
  4.  It is recommended that the plugs for the heating element and the plug for the submersible pump both be plugged into a serge protector. This will provide an on-off switch. Never turn the heating element on unless there is water in the retort.
  5.  With the lid off and the inside basket in place, add plant material. Pack it as tightly as possible. Once plant is inside the retort, add water. Add enough water to ensure that the water level as evident in the sight glass is at least half way up the glass. Add the water slowly .
  6.  After plant matter and water are in the retort, place the lid on top. Do not tighten the lid as yet. The lid bolts should be in place but not tightened down.
  7.  Position the condenser. The legs of the condenser should be even with the legs on the retort. The thermometer should be facing front. The spout on the condenser should be facing front as well. Connect the condenser and the retort by tightening the Bird Beak connector
  8.  Add water to the condenser. Water is either pumped in or piped into the bottom nipple of the condenser. Water will exit from the nipple on top.
  9.  Turn on the heating element in the retort. It will take about 1/2 hour to build up temperature. When water starts to boil, check the lid for steam leaks. if you discover a steam leak, gently turn the lid bolt closest to the steam leak. Stop tightening when the leak ceases. There is no need to over tighten the lid. It is complete with a specially designed gasket.

Distillation will take about 1 hour. The distillate should be captured in the separatory funnel. In most cases, the essential oil will separate passively and float to the top. The waters which have been separated can be reintroduced into the retort through the water inlet at the top of the retort. Steam will initially come out of the water inlet, but once you start pouring water in the steam will exit elsewhere. BE CAREFUL!! This is very hot! Be sure to wear gloves.

To clean your distiller allow the distiller to cool. Make sure the unit is switched off, or unplugged. Disconnect the condenser first. Loosen the lid bolts and remove the Bird’s Beak. Open the clean out valve. Hot water will pour out the bottom. Remove the metal rods protecting the sight glass. Lift the retort being careful to avoid breaking the glass. Tip the retort over to empty the spent plant matter. Gently pull the handle of the basket to remove plant matter. You can also leave the retort in place, and with the bird's beak off, remove the plant material. Your spent plant material is very hot. Wear gloves and BE CAREFUL!

If you plan to distill a different type of plant, you will need to clean the still. This is easily done by adding water to the retort, connecting the condenser (without circulating water) and turning on the heating element. The water inside will boil, and the steam will clean out the retort and the condenser. Steam will exit the condenser instead of distillate. Remember to not add water to the condenser for cleaning purposes.

References

Most of the material taken from a White Lotus Aromatics newsletter. http://members.aol.com/somanath/fragrant.html

Drawings of kit from The Food and Agriculture Organization of the United Nations. http://www.fao.org/

Home stills from The Essential Oil Company. http://essentialoil.com/distiller.html

 

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