The liquid aromatic essences we encounter in our daily lives, such as perfumes and fragrance essential oils, are extracted from precious oils obtained from plant raw materials. However, most people are unaware of how these fragrance essential oils are extracted. For example, the familiar rose essential oil is extracted within 24 hours after picking fresh roses in the morning, resulting in a brownish-yellow rose essential oil. About five tons of rose flowers can only produce two pounds of rose oil, making it one of the most expensive essential oils. This article aims to share the methods of extracting fragrance essential oils to provide some knowledge.
Extraction Method One: Distillation
This is the most commonly used method for extracting essential oils from aromatic plants, with 95% of aromatic plant essential oils obtained through distillation.
In this method, plant parts containing aromatic substances (flowers, leaves, wood chips, resin, bark, etc.) are placed in a large container (distiller). Heat is applied to the bottom of the container through combustion or steam injection. When the hot vapor fills the container, it evaporates the aromatic essential oil components stored in the plant along with water vapor. As the steam passes through the condenser at the top, it is then introduced into the condenser. The condenser is a spiral tube surrounded by cold water to cool the steam into an oil-water mixture, which then flows into an oil-water separator. Lighter oil floats on the water surface, while heavier oil sinks to the bottom, leaving behind pure hydrosol. The essential oil and hydrosol are further separated using a separating funnel.
Distillation is divided into water distillation, water-steam distillation, and steam distillation, and the method should be chosen based on the characteristics of different materials.
Water distillation involves placing the material to be distilled on a sieve plate inside the distillation pot, with water poured underneath the sieve plate. The water can be heated directly, steam can be introduced to heat the water, or an electric jacket can be used to heat the water, generating steam for distillation.
Water-steam distillation involves placing the material to be distilled in the distillation pot, with water poured into the pot. The ratio of water to material varies depending on the material. The method is similar to water distillation.
Steam distillation involves placing the material to be distilled on a sieve plate inside the distillation pot, with saturated steam introduced below the sieve plate to achieve distillation.
Extraction Method Two: Enfleurage
This is a very refined extraction method, but it is less commonly used today due to its time-consuming nature.
First, petals rinsed with water are spread on a glass plate coated with animal fat or vegetable oil. The glass plate is framed with wood, and the plates with covered petals are stacked one by one. Then, the stacked wooden frames with glass plates filled with petals are placed in the sun, allowing the heat to release the essence from the petals.
Every one to two days, the glass plates are flipped. Yellowed and withered petals are discarded, and fresh flowers are laid on the plates. This process is repeated until the fat on the glass is saturated with released essential oil. At this point, this fat is called enfleurage. Subsequently, the oil is washed away from the fat using volatile pure alcohol to obtain the highly expensive absolute oil.
Extraction Method Three: Solvent Extraction
Compared to distillation and pressing methods, this extraction method is relatively expensive due to its complex process, resulting in a lower yield of essential oil. Solvent extraction is commonly used for delicate and fragile plant petals or resin extraction.
First, a solvent such as petroleum or benzene is used to extract the volatile and non-volatile components of crushed plant material. The resulting mixture is filtered again with a solvent, and after the solvent evaporates, a semi-solid waxy substance containing alcohol is produced. Later, alcohol is selectively used to extract the essential oil components from the waxy substance, resulting in high-quality, concentrated plant essential oils. Therefore, the essential oil components obtained by solvent extraction may vary depending on the characteristics of the plant material, and their prices will also differ.
Solvent extraction is used to extract essential oils from plant parts such as flowers, petals, and buds. The product obtained after extraction is called “concrete.” If the extraction is from the natural secretions of plants, such as gums, resins, or sap, the resulting product is called “resinoid.” After extracting the “resin” or “concrete” again with alcohol or alcohol, the second-stage product obtained is called “absolute oil.” Later, the oil is washed away from the fat using volatile pure alcohol to obtain the highly expensive absolute oil.
Extraction Method Four: Expression
The majority of citrus essential oils, such as sweet orange, bergamot, grapefruit, and tangerine, are extracted using this method because most citrus essential oils cannot withstand the heat of distillation, which would destroy their essential components. However, lime, also a citrus fruit, is distilled because the distilled lime essential oil has a milder fragrance and better quality compared to the expression method.
Until the 1930s, expression was primarily done manually by hand. The method involved rubbing citrus peel back and forth with natural sponges to squeeze out the juice. The essential oil released from the peel was completely absorbed by the natural sponge, and then workers squeezed the saturated sponge to extract the essential oil into collection bottles. These cleaned sponges were then sold as aromatic sponges.
Today, most essential oil manufacturers use machines instead of manual labor due to cost and production considerations. However, in the Grasse region of southern France, people still manually extract citrus essential oils, and natural aromatic sponges can still be found in the streets of Provence.
Extraction Method Five: Supercritical Fluid Extraction
Principle: Supercritical carbon dioxide has special solubility for plant essential oils, and its solubility is related to density, which can be adjusted by temperature and pressure to precipitate the essential oil.
Process: Using specific equipment to make carbon dioxide reach a supercritical state (temperature above 32°C, pressure above 7.2 megapascals), extract the essential oil from the material, and then separate the essential oil from the extraction agent through temperature and pressure changes. Therefore, supercritical extraction consists of two processes: extraction and separation.
Extraction Method Six: Fat Separation
This is an ancient extraction method originating from France. This method takes advantage of the ability of fat to absorb the essential oil contained in plant petals, mainly used for extracting petals of plants. The method involves placing cleaned fresh flowers on a glass plate covered with a thick layer of fat (usually vegetable oil). The glass plates with flowers are then stacked, tied together, and placed in the sun to allow the heat to melt the flowers and release the essential oil. Afterward, the flipping time is determined based on the type of flower, removing old flowers and laying new ones, repeating this process until the fat completely saturates with the essential oil. Then, alcohol is used to wash away the oil from the fat, leaving behind the essential oil, belonging to the highest grade. This method is quite complex and time-consuming, and it is rarely used today.
Extraction Method Seven: Subcritical Extraction
Subcritical fluid extraction technology uses subcritical fluids as the extracting agent in a closed, oxygen-free, low-pressure container. Based on the principle of similar solubility of organic substances, the essential oil components in solid materials are transferred to the liquid extracting agent during the soaking process. The extraction agent and the target product are separated through the process of reducing pressure and evaporation, ultimately obtaining the desired product.