Distillation converts the essential oils in plants into a vapor, then the vapor is condensed to a liquid and decanted. This is the most common / cost effective method, however, this method requires heat which can damage a few very fragile plants. Care should always be taken with temperatures and length of heat exposure.
Hydro Diffusion - H/D
The plant materials are placed on a wire mess support inside a still and steam is forced inside, above the plant materials. The steam is then condensed in the still and the water / oil mixture is collected at the bottom where the oil is then decanted. This method often uses less steam, less time and produces a higher yield.
Steam Distillation - S/D
The plant materials are placed inside a still and steam is forced inside, usually under the plant materials. The steam heats the oils in the plant matter until the plant cells rupture and the vapor escapes. Steam temperature and pressure are carefully controlled so as not to damage the essential oils. Next the steam enters a condensing unit and the oil is decanted.
Water Distillation - W/D
The plant materials are placed inside a still and immersed in water which is then boiled. Pressure is often used to lower the boiling point. The water provides some protection from overheating so this method is sometimes prefered to S/D. The water is cooled and the oil decanted. The remaining water is known as "hydrosol" or "floral water" which also has therapeutic value. Esters break down into alcohols and carboxylic acids so this method is not suitable for botanical matter with high ester content.
Cohobation - C/H
Cohobation is mainly used to extract rose oil. Phenyl ethyl alcohol (responsible for scent) dissolves into the water during W/D. Since it is soluble it must be distilled from the water and then mixed with the decanted oil in the correct proportion to create Rose Otto.
Rectification - Rec
Rectification occures when essential oils are re-distilled to remove impurities. Oils marked as "double-distilled" have undergone this process.
No heat or chemicals are used for oil extraction. Beware that refining is often done with heat and / or chemicals which may degrade oil quality and / or change some of their properties / chemical make-up.
Cold Pressed - C/P
Oils from olives, nuts, and seeds are commonly extracted this way. This method produces very high quality oils.
Fractional Distillation - F/D (Écuelle à piquer)
This is an easy way to extract citrus oils. The fruit is placed on a prod and a spiky device is then rolled over the skin rupturing the oil cells. The oil drains into a collection pot. The collection is allowed to stratify and the oil decanted.
Machine Abrasion- M/A/E
Citrus rinds are placed into a centrifugal separator. This method could alter the essential oil properties if done for too long because of enzymatic reactions with other cell contents.
Sponge Extraction - E/S/E
Citrus rinds and piths are soaked in warm water. Rinds are then squeezed onto a sponge, dropping both water and essential oils. The sponge will help concentrate the oils and filter out pulp. When saturated, squeeze the sponge into a container and decant.
Chemical solvents, fats, and/or carbon dioxide are used to successfully extract oils from plants which produce essential oils in very low concentrations. This method is also used to extract resins. Often this process requires the further seperation of oils from organic waxes and pigments.
CO2 Extraction - CO2
At 33° Celsius and 200 atmospheres pressure CO2 has both liquid and gas like properties. In this state it is said to be "hypercritical". Hypercritical CO2 provides an excellent solvent for essential oil extraction because of the lower temperature and speed of extraction. Furthermore, CO2 is naturally a gas so it can be easily removed from the essential oil by lowering it's pressure. This method is very expensive due to the equipment required.
Phytonic Process - P/P
This method is even gentler than CO2 because it extracts the oils at even lower temperatures. It was developed in England and requires the controversial use of fluoro-hydrocarbons.
Solvent Extraction - S/E
Petroleum ether, methanol, ethanol and/or hexane are often used to extract oil from fragile botanical matter which could not survive high temperatures required in other methods. Oils extracted via this method are highly concentrated and closely reflect their original scent. Solvent residue can be a concern (as high as 20% present in some essential oils!), especially when benzene is used in the extraction process. Furthermore, benzene is carcinogenic so beware of oils that have been extracted in that way! Conversly, hexane often leaves a residue of about 10ppm. Hexane may cause impaired fertility, may cause CNS depression, and prolonged exposure may cause serious health damage, however, at 10ppm, it shouldn't be a concern.
Solvent Extraction Enfleurage - S/E/E
This is a very time consuming, expensive extraction method sometimes used for delicate flowers like violet, tuberoses and jasmine. Glass cases are filled with highly purified odorless vegetable or animal fat. Botanical matter (usually flowers) is placed onto the fat and pressed in. Often these glass cases are left in the sun to aid in this process. After a few days the essential oils will leech into the fat. Botanical matter is then removed and replaced. This process is repeated several times until the fat is saturated. The resulting fat is then washed with alcohol to seperate the essential oil. The alcohol evaporates off and the essential oil is left over. The fat is often then used in soap making.
Solvent Extraction Maceration - S/E/M
Flowers are soaked in hot oil which ruptures the flowers' cell membranes. The essential oil is absorbed by the hot oil. The botanical matter is removed and the oil cooled and then decanted.
|Maceration - Mac
The soaking or steeping of a substance in a liquid, at the ordinary temperature, is termed maceration. It is almost exclusively applicable to organic substances, being most frequently resorted to as a means of hastening and facilitating the after solution of the extractive parts of hard, compact or impervious wood, roots, stems and leaves by the more active methods of DISPLACEMENT or of EBULLITION. It is employed when the soluble principles are alterable by heat: and is also made use of to effect the solution of a substance containing several principles, the solubility of which varies with the temperature applied, as it leaves those which are not taken up in the cold to be acted upon by the aid of heat.
The mode of performing the process is merely to place the solvent and the substance to be dissolved, together in a vessel, and to allow them to remain a longer or shorter time, according to the nature of the substance. For ordinary purposes a loosely covered pan of blue stone-ware is very convenient. Chemical and Pharmaceutic Manipulations pdf pg. 296. For a historic account of maceration please see The American Journal of Pharmacy - Vol 82 - pgs 32-42.
This process is likewise applicable almost solely to organic substances. Instead, however, of the solid remaining in contact for a length of time with the solvent, the latter is first heated to boiling and then poured upon the former. After having cooled, the liquid may be decanted or pressed out.
This mode is used for the exhaustion of flowers, leaves, roots, seeds and other substances of delicate texture, which are easily penetrable and readily yield their soluble matters; and especially for the purpose of extracting volatile ingredients. The heat applied to the solvent increases its energy; but as the material is only in contact for a limited time, the interval between the commencement and completion of the operation is not sufficient to affect the material or solution, even though one or more of its components are alterable by heat.
In pharmaceutical operations, this process is generally conducted in cast iron flask-shaped vessels with handles, enamelled on the inside and fitted with a tight cover, which is to be kept in its place from the addition to the cooling of the solvent. For small operations, a beaker glass covered with a capsule, or a yellow earthenware stew pan with lip and cover, such as can be had at the crockery shops, are admirably adapted.
Chemical and Pharmaceutic Manipulations pdf pg. 297
This process is used primarily for extracting tar from trees. Pieces of wood are taken from a live tree. Next, the wood is placed under some type of metal hood. Sometimes inverted metal pots are used. Next, a large metal funnel is placed above the wood and below the metal hood. The funnel often drains into a pipe which goes through the kiln bottom (below the fire) and drips into a tall glass container. The wood is then burned and tar from the smoke collects on the bottom side of the hood and drips down into the funnel, down the pipe, and into the glass container. Once the glass container is full it is removed, allowed to cool, covered, and allowed to sit undisturbed for 6-8 weeks. After that time the tar should seperate into 3 distinct layers; thick tar on the bottom, a watery liquid middle, and a dark oil layer on top. The top layer is the essential oil.
Some essential oils can be difficult to extract thus requiring high temperatures. Essential oils are very sensitive to heat so it's possible to lower extraction temperatures by altering pressure. Vacuum distillation refers to this process and often requires special equipment.
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