Distillation & Extraction with Rose Oils
The first record of rose distillation can likely be traced back to the eighth and ninth centuries, where rose water was a prized commodity by the Persian empire (Guenther, E. (1952) The Essential Oils. London: Macmillan). The distillation of rose petals to extract rose essential oil is a complex and delicate process. Because the rose petals contain very little essential oil (about 0.02%), extracting large amounts of oil is difficult. It takes an average of 60,000 roses to produce just one ounce of oil, and ten thousand kilograms of rose blossoms to produce one kilogram of oil. With such a delicate, valuable oil, maintaining highly-controlled conditions for distillation is crucial. Additionally, while the essential oil of most plants can be steam-distilled through passing steam over the plant material, rose petals tend to stick together under steam to form a compact mass. Consequently, the best distillation method for rose essential oil extraction is hydro, or water, distillation (Tucker, source, 2014).
Hydrodistillation of rose petals is a two-part process. Distilled rose essential oil is composed of both direct oil (decanted oil) and water oil (recovered oil from the distillation water). Initially, the fresh rose petals are hydrodistilled and the rose oil and water are collected together. The oil separates and floats to the surface of the water where it is removed and separated from any water. The remaining rosewater, known as rose hydrosol or hydrolat, is then redistilled (a process called cohobation). The additional oil obtained from this second distillation is called recovered oil or rose water oil. The rose essential oil from the first distillation and the rose water oil are then combined to produce the final rose essential oil. The rose oil is then placed into clear glass containers and exposed to sunlight for a short period of time. The sunlight acts to raise any impurities to the surface, which can then be skimmed from the top, leaving behind only the high-quality rose otto. Typically, this final oil is composed of approximately 75% water oil and 25% direct oil (Guenther, E. (1952) The Essential Oils. London: Macmillan).
The rose hydrosol obtained from the second distillation becomes the commercial product rose water (Panda, Cultivation and Utilization of Aromatic Plants (Google eBook), 2005). Commercially-produced rose water is sometimes diluted with additional pure water (often in a 1:1 ratio). Rose water is also produced by adding a small amount of rose oil to pure water, but this is not a true rose water (ITC, source).
Solvent Extraction – Rose Concrete and Rose Absolute
While the distillation of rose petals yields true rose oil (rose otto), the extraction of rose petals using chemical solvents produces two important products: rose concrete and rose absolute. Rose concrete is a semi-solid, red-colored, waxy material that is typically further refined into rose absolute - the final product used in perfumery and in the manufacturing of cosmetics where the fragrance of rose is desired.
Rose concrete is produced by placing freshly harvested rose petals into a large vessel that can be sealed and charged with a non-polar solvent such as hexane (n-hexane or similar hydrocarbon solvent). The petals are then stirred and the extraction takes place. The essential oil components, other aromatic components, plant waxes, pigments, and oils are extracted from the petals, and then the solvent and extract are separated from the rose petals so that another extraction can take place. The extractions are then combined and the solvent is vacuumed off for reuse, whereby the finished concrete results.
Rose concrete contains approximately 60% absolute and is rich in constituents, containing about 166 components of which 30 or so are hydrocarbons. It takes about 350 kg of rose petals to produce one kg of rose concrete. The concrete can be sold as is or stored for later refining into rose absolute.
In order to produce rose absolute, the concrete is subjected to a series of washings with a polar solvent, typically ethanol (ethyl alcohol). The ethanol helps to extract the aromatic oils from the concrete while leaving behind the non-polar plant waxes. Finally, the ethanol is evaporated off under low vacuum to leave behind the rose absolute—a pure, highly fragrant concentration of aromatic compounds.
Rose CO2 Extract
Supercritical fluid extraction using CO2 (CO2 extraction), is a relatively new method of extracting aromatic and flavoring compounds from plants. CO2 extraction is rarely used to extract rose oil. This process uses carbon dioxide at very high pressure, typically the pressure that the CO2 gas turns into a liquid (the supercritical state). CO2 is used as a solvent that is pumped through a heat exchanger in order to reach the extractor in the supercritical state and injected into a tank that contains the rose petals (or alternatively the rose concrete). At the supercritical state where the gas turns to liquid the solvent breaks the cell walls of the rose petals and releases the constituents. During extraction, the supercritical CO2 passes through the plant matrix bed and dissolves the soluble compounds. The mixture of CO2 and soluble compounds are separated in flash tanks and the CO2 is then cooled and compressed and returned to the extractor unit. The process occurs at ambient temperatures without any added heat, which is beneficial for retaining the original plant constituents and not damaging or changing them.
Carbon dioxide is a colorless, odorless, highly pure, safe, non-flammable and recoverable gas that can be completely removed from the oil after the extraction process is complete. Rose petals are rarely extracted directly using CO2 because CO2 extraction units are rarely situated near the rose fields. However, CO2 is being used to extract rose concrete (the result of the first step in the production of rose absolute), since the rose concrete can easily be shipped to a CO2 extraction unit anywhere that it is located.
Rose Organic Extract
A few essential oil companies also produce an organic rose extract, also known as the French rose “extrait.” Organic extracts are extracted by a similar method to rose absolute in a two-step process, however in this case they use benign solvents rather than hexane, and the result is often a softer fragrance than the intense aroma of rose absolute. Solvent used must be certified organic such as a vegetable oil and the ethanol used during the second step of the process also needs to be certified organic. The aroma is also less strong than that of rose essential oil. However, rose organic extracts are extremely gentle, and because the extraction method does not use hexane, or similar chemical solvents during the first step, organic rose extracts are certified organic products. Rather than being an orange or reddish color as rose absolute is, rose organic extracts are greenish, likely due to the solvent not being as aggressive as hexane and not extracting as much colorant from the rose petals. The cost of rose organic extracts are in between the cost of rose absolute and rose otto and find their best use in the specialty aromatherapy and natural perfume market.
One of the newest methods of extracting rose essential oil is the phytonic process, which uses a new solvent based on hydrofluorocarbon-134a to extract aromatic constituents from plant matter. This method was developed in the United Kingdom by British microbiologist Dr. Peter Wilde in collaboration with a multinational chemical company. According to scientific reports on this method, the phytonic process “offers significant environmental advantages and health and safety benefits over traditional processes for the production of high quality natural fragrant oils, flavors, and biological extracts” (International Centre for Science and High Technology (ICS), source, 2008).
Rose attar (gulab attar) is a unique aromatic rose oil that has been made in India for at least several hundred years and possibly for millennia. It is still produced in small quantities in March and April by specialty perfumers who operate their family business by extracting rare flowers and other plants in the traditional way. The method for producing rose attar consists of hydrodistilled the rose petals in a copper vessel called a deg. The deg is heated from a fire below and the steam rises and exits the deg through a hollow bamboo pipe knows as a chonga, and is delivered to the receiving vessel called a bhapka. The bhapka is unique in that it is not an empty vessel that collects the hydrosol and rose essential oil, rather the bhapka (traditionally) has sandalwood oil in it, and it sits in the cool water. Thus the bhapka acts as the receiving vessel and as the condenser such that when the steam carrying the aromatic constituents of the rose petals enter the bhapka, the volatile vapors condense into the sandalwood oil. Thus the resulting attar is a unique blend of sandalwood oil that has “captured” the rose essence. The rose oil thus captured has a different set of constituents than a typical distilled rose oil due to the unique distillation process and the unique fixative qualities of sandalwood oil. Rose attar is highly valued and becoming harder to find as the traditional perfumers are becoming rarer and sandalwood oil is becoming harder to obtain. Due to the high cost and difficulty in obtaining good quality sandalwood oil other fixative oils are also used such as vetiver and liquid paraffin.