In order to ensure that plant-based raw materials meet the processing requirements, screening and grading, storage and aging, fermentation and aroma generation, impregnation, drying or crushing are required before processing, which is called pre-treatment. For example, the aging and aroma generation of iris before distillation, the immersion of rose water or salt water, etc. There are four commonly used extraction methods.
1. Steam distillation method:
Suitable for raw materials where the aroma components do not undergo significant changes due to steam heating. This method is easy to implement and therefore has a wide range of applications. By utilizing the volatility of essential oils, although their boiling points range from 150 to 300 ℃, water vapor can be distilled below 100 ℃. Before distillation, the raw materials should be properly dried and crushed, and scooped into a steamer with a sieve plate. Water vapor should be introduced from below the sieve plate, and the rising water vapor should evenly pass through the material layer. The essential oil should escape from the plant tissue through water infiltration, and rise with the water vapor. It enters the oil-water separator through the gooseneck tube and condenser tube above the distillation pot, and finally separates the essential oil.
2. Extraction method:
If the aroma components are easy to deteriorate when heated, or part of the aroma components are dissolved in water, it is not suitable for raw materials extracted by steam, especially for some fresh flower raw materials, which have low essential oil content and can only be extracted at a temperature lower than that of the Steam distillation method, the extraction method should be used. The most commonly used method is volatile solvent extraction. Such delicate flowers as roses, jasmines, white orchids, violets, acacia, daffodils, carnations, Cytisus scoparius, etc. are processed in this way.
3. Cold pressing and grinding method:
A method for obtaining essential oils from citrus fruits or peels. After pressing and grinding, the oil pocket can be fractured or punctured at room temperature, allowing the essential oil to flow out. The essential oil released from the oil sac flows out together with broken fruit skin tissue, cell debris, and cell fluid spray water, and then separates and clarifies the oil, water, and debris to obtain the product. The implementation methods include: manually pressing the fruit peel, and using a sponge to absorb and recycle the essential oil that flows out; The manual filing method utilizes a copper file press with sharp edges to manually file and press the essential oil into a funnel for recycling; Mechanical pressing method, utilizing various filing or pressing machines designed based on the principle of filing, such as roller presses and screw presses; Mechanical grinding method, which involves grinding and extracting oil from the outside of the entire fruit.
4. Adsorption method:
The earliest applied adsorption method was the cold adsorption method. Put the flowers that are still alive after picking, such as jasmine and Agave amica, on the flower frame coated with refined oil, and then put the flowers stacked in the low-temperature room. After a period of time, the flowers need to be replaced, and after multiple changes, the oil adsorbs the fragrance components of the flowers to saturation. Then, ethanol is used for extraction to produce a product called balsam oil. In addition, using the principle of activated carbon adsorption, the above types of flowers are picked and placed in an adsorption chamber with an activated carbon bed layer on top. Pure air with a certain temperature and flow rate is introduced, and the air passes through the flower layer to bring the fragrance components released by the flowers into the activated carbon bed layer for adsorption. After a certain period of time, the saturated activated carbon is desorbed with a solvent to produce essential oil. Recently, various new porous polymer adsorbents have been developed, and adsorption technology has further developed. The use of liquefied carbon dioxide as a solvent for desorption has significantly improved the quality and yield of essential oils.
