The sandalwood tree’s precious sandalwood oil is located within the tree’s heartwood, and the older the tree, the high proportion of heartwood it contains. Because the oil is held tightly within the wood, a distillation process is required, in which the wood is first ground to a powder form. Distillation methods vary, ranging from today’s steam distillation to the more traditional hydro (water) distillation, also including CO2 extraction, absolute extraction, and an array of new technologies.
Today most sandalwood companies use steam distillation in order to extract sandalwood oil. Steam distillation is a process in which steam heated at extremely high temperatures (usually around 140-212˚ F) is passed through the powdered wood. The steam releases the sandalwood essential oil that is locked within the cellular structure of the wood. The mixture of steam and oil then flows through a condenser and cools, yielding a layer of oil and a layer of water. The sandalwood essential oil separates from the hydrosol (floral water) rises to the top so it can then be collected. The distillation process for sandalwood oil takes anywhere from 14 to 36 hours, longer than for many other essential oils. Despite the fact that this method requires a longer process than other distillation methods, it’s known to produce superior quality oil, yielding 84.32% santalol (Sandalwood Research Network [SRN], http://staff.sjp.ac.lk/upul/files/srn_025.pdf, 2010).
Hydro, or water, distillation is the traditional method of extracting sandalwood essential oil. Instead of steam passing through the powdered wood, in hydro distillation the powdered wood is immersed in water to soak. The water is then boiled, often heated over an open fire. The essential oil eventually floats to the surface, above the hydrosol, where it can be collected. Some disadvantages to this method include the fact that hydro distillation requires heating a large quantity of water, which increases the costs and time needed for sandalwood distillation. Also, the temperature of the boiling water is difficult to control, which causes the rate of distillation to vary and often causes the oil to be “burned,” lessening its quality (Erowid, http://www.erowid.org/archive/rhodium/chemistry/3base/safrole.plants/moc/distillation.html, 1992).
CO2 extracts, also known as supercritical CO2 extracts or supercritical fluid CO2 extracts, are pure plant extracts produced from a fairly new and highly efficient extraction process. CO2 extracts are similar to essential oils and can be used in aromatherapy or perfumery. The CO2 extraction method involves pumping pressurized carbon dioxide into a chamber filled with the sandalwood’s powdered heartwood. When carbon dioxide is subjected to pressure it possesses liquid properties while remaining in a gaseous state. Because of these liquid properties of the gas, the CO2 acts as a solvent, releasing the sandalwood oil from the wood. While steam distillation requires temperatures of 140˚-212˚ F, CO2 extraction only requires temperatures of around 95˚-100˚ F ((Eden Botanicals, http://www.edenbotanicals.com/co2-extracts-supercritical-extraction-essential-oils.html, 2014.) Oil yielded in CO2 extraction contains about 82.5% santalol, while steam distilled oil contains about 84.32% santalol, and hydro distilled oil contains about 52.59% santalol (Journal of Natural Products, http://www.journalofnaturalproducts.com/volume4/22_res_paper-21.pdf, 2011).
Absolute (solvent) extraction is a method of extracting essential oils that are most often used by the perfume industry, due to the strong aroma of the oil extracted with this process. Solvent extraction uses solvents, such as petroleum ether, methanol, ethanol, or hexane, to extract the oil from the plant. The chemicals release not only the plant’s oil, but also chlorophyll and other plant tissue, resulting in a thick, highly concentrated extract known as a concrete. The concrete is then mixed with alcohol to extract just the plant’s essential oils (Natural Association for Holistic Aromatherapy [NAHA], http://www.naha.org/explore-aromatherapy/about-aromatherapy/how-are-essential-oils-extracted, 2014).
This distillation method is less often used to produce therapeutic oils for aromatherapy such as sandalwood essential oil, because chemicals such as hexane, acetone, di-methylene-chloride, and others are used in the process. This method is often used for jasmine, carnation, gardenia, jonquil, violet leaf, narcissus, mimosa, and other flowers which are too delicate to be processed through steam or hydro distillation. (NAHA, http://www.naha.org/explore-aromatherapy/about-aromatherapy/how-are-essential-oils-extracted, 2014).
Absolute extraction is rarely used to extract sandalwood. In a recent study by Australia’s Sandalwood Research Network, the oil produced through absolute extraction methods—using the chemical solvents benzene, diethyl ether, ethyl alcohol, and toluene—was found to yield comparable amounts of santalol as steam distillation. Sandalwood oil extracted using the solvent ethyl alcohol yielded around 84% santalol, about the same as oil extracted through steam distillation. However, the aroma of oil extracted through chemical solvents was consistently found to be much “less pleasant” than the aroma of oil extracted through the more time-consuming steam or water distillation methods (Sandalwood Research Network [SRN], http://staff.sjp.ac.lk/upul/files/srn_025.pdf, 2010).
The phytonics process is one of the most recently developed technologies for essential oil extraction. Advanced Phytonics Ltd. (Manchester, UK) developed and patented this method, and a recent essential oil extraction report explains that “The products mostly extracted by this process are fragrant components of essential oils and biological or phytopharmacological extracts which can be used directly without further physical or chemical treatment.” The phytonics process involves the solvent hydrofluorocarbon-134a, which has a boiling point of -25˚ C (-13˚F). This solvent is neither flammable nor toxic, and it does not deplete the ozone layer. By most standards, this substance makes for a “poor solvent,” as it does not mix with many other chemicals such as mineral oils or triglycerides. However, since this solvent also does not dissolve plant wastes, it is perfect for use in the extraction of essential oils.
Other advantages of this extraction technology are numerous; for example, unlike other methods such as steam or water distillation which employ high temperatures, the phytonics process “is cool and gentle” and the products are not exposed to excess, possibly harmful temperatures. Because the phytonics process also uses minimal electricity and does not release any harmful emissions into the atmosphere, it is thought to be much less threating to the environment than other extraction methods (International Centre for Science and High Technology, http://institute.unido.org/documents/M8_LearningResources/ICS/14.%20Extraction%20Technologies%20for%20Medicinal%20and%20Aromatic%20Plants.pdf, 2008).