Steam distillation : This is the most commonly used method of refining essential oils. Fresh or dried plant materials are placed in a still, water or water vapor is added, and the water vapor is passed through the plant material by heating at high temperatures, bringing out its aromatic components. The water vapor containing the aromatic components is cooled into a liquid in a condenser, and then they are separated according to the difference in density of the water and the essential oil. The remaining water is called hydrosol and also has a certain aromatic value
Pressing method: Mainly used for citrus fruits, such as lemons, oranges, etc. The peel is chopped or crushed, placed in a press, and pressed vigorously to break the oil cells, releasing the essential oil and juice. The mixture is then introduced into a centrifuge, where centrifugal force is used to separate the essential oil and juice
Solvent extraction: Plant raw materials are mixed with volatile organic solvents for cold or hot soak extraction. After the extract is filtered, the solvent is removed by distillation or vacuum distillation to obtain a semi-solid substance containing aromatic components, and then processed to obtain a high-concentration essential oil product.
Supercritical fluid extraction: The special solubility of plant essential oils is extracted by using carbon dioxide or other fluids in a supercritical state. By adjusting the temperature and pressure, the supercritical fluid dissolves the aromatic components in the plant, and then the temperature and pressure are reduced to return the fluid to a gaseous state, and the aromatic components are precipitated out, and finally a high-purity essential oil product is obtained
Pros, cons and application scenarios of each method
Steam distillation: suitable for most plant raw materials, simple to operate, suitable for large-scale production. However, some spice plants with high ester content are not suitable for this method because esters are easily hydrolyzed.
Pressing method: suitable for citrus fruits, simple to operate, suitable for small-scale production. The product is of high purity, but it is only suitable for specific types of raw materials.
Solvent extraction: suitable for occasions that require high-purity essential oils, such as high-end perfume making. However, the use of solvents may have a certain impact on the environment, and the operation is complicated.
Supercritical Fluid Extraction: Ideal for applications that require high purity and quality essential oils. The operation is complex and the equipment is expensive, but it preserves the natural aroma of the plant and is not affected by heat and solvents.
