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Extraction method of plant essential oil

Posted time:2022-06-16 Page View:249

1) Raw material collection

For most plants, harvesting undamaged leaves or twigs without dewdrops at 9-11am before flowering is more effective. The sooner the raw materials used for extracting essential oils are collected, the better. For example, the work of picking roses must be carried out in the morning before the sun comes out. And the harvesting place must be very close to the refinery, and workers can send it directly after harvesting. The shorter the time, the better. The raw materials used to extract essential oils vary according to the structure of the plant oil glands, and the collection methods are also different.

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1. Maintenance of unscented flowers


Jasmine, jasmine grandiflora, tuberose, etc. are the collection of mature flower buds that are about to open. It does not produce fragrance before it opens, and only through the process of respiration and metabolism, and after a certain period of time, the flower buds open and fragrant. During the above functions and processes, the flower buds will continuously release a certain amount of heat. During transportation and storage, if not properly maintained, the flower buds will ferment and deteriorate due to excessive heat. Generally, during transportation, the flower buds are often loosely packed in bamboo baskets, and sometimes a bamboo ventilator is set in the middle of the baskets. During the storage process, the flower buds are placed in a thin layer for maintenance, and the thickness of the flower layer is not more than 5cm.


Full bloom and fragrance of flower buds are related to the following conditions:


(1) The air on or around the flower layer should be properly circulated.


(2) The flower bank for storing flower buds should have a suitable room temperature, generally 28 to 32 °C.


(3) Appropriate relative humidity should be maintained in the flower library, generally 80-90%. In order to make the mature flower buds open evenly and uniformly, the flower layer should be gently turned up and down at regular intervals. Large-flowered jasmine buds should be sprayed with mist water in the hot and dry July to August to make them bloom better and have a stronger aroma.


2. Maintenance of blooming flowers


White orchid, yellow orchid, gardenia, rose, ginger flower, etc. are the flowers that just opened on the day of collection. These open flowers already have a fresh and strong fragrance, but they are still undergoing the metabolic process and are still releasing heat, so once collected, they should be sent to the factory in a loose manner with bamboo baskets immediately to maintain the quality of the aroma and reduce the loss of aroma. If it is too late to process, it must also be placed in a thin layer for maintenance, so that the flowers will not deteriorate due to heat fermentation.


3. Preservation of fresh leaves


Generally, fresh leaves should not be processed immediately after they are collected. They should be placed in a thin layer for a certain period of time. Sometimes they can be placed in a semi-dry state before processing. For tortoise leaves, orange leaves, mint leaves, etc., after being placed for a certain period of time (several days), the oil yield is often 5-20% higher than the original fresh leaves (calculated by fresh weight). However, in the process of transportation and storage of fresh leaves, like flowers, it is necessary to prevent heat and fermentation, otherwise it will affect the oil yield and quality. After the fresh leaves are placed in a thin layer for a certain period of time, a part of the water on the leaf surface is evenly lost without being very dry, and the cell pores on the leaf surface are enlarged, which is conducive to the diffusion of essential oils and improves the oil yield.


Delicate fresh leaves, such as geranium, do not need to be placed, and should be processed immediately after collection. Even if such leaves are stacked for an hour, their fragrance will change greatly. Fresh leaves for long-term preservation are often dried in the shade or sun-dried after collection, such as perilla leaves, etc., but during the drying process, a part of the essential oil will be lost, especially in the sun-drying method, so the thin-layer shade-drying method is adopted. should.


4. Collection and preservation of resin


Take the collection of frankincense as an example. People began to collect frankincense in early August. They used a long machete to make a few cuts on the tree without hurting the small branches. The day after the cut, people would see some nutritious. The sap flowed out drop by drop, which gradually condensed into frankincense. The frankincense hardens and then falls to the ground, which is why the underside of the tree is so clean. The peak season for frankincense is mid-August, when the weather is sunny and dry.


(2) Distillation method of plant essential oil


It is documented that in the past most essential oils were produced in Egypt using solvent extraction methods. However, according to the research of the newly unearthed still pot, the Egyptians living in Mesopotamia had already used distillation technology to extract essential oils as early as 3,500 BC. However, we should attribute the invention of distillation technology to the Arab alchemist (also a physician), who lived between AD 980 and 1037, because he was the one who mastered all distillation technology, and his craft was so perfect that It has not changed for hundreds of years. Its distillation principle is to first convert volatile liquid (essential oil) into gas, and then cool the gas into liquid. This is the most common and effective method we use today for the production of essential oils.


Distillation technology also has shortcomings. It can't help when extracting some materials that are easily changed by heat, or when some oils are difficult to extract using this technology.


1. Water distillation method


In the manufacture of essential oils, using the hydrodistillation method, the plant material is completely immersed in water and allowed to stand until the water boils. To some extent, this method protects the extracted oil because the water surrounding the oil acts as a barrier to prevent the oil from getting too hot. When the concentrated ingredients cool down, the water and the essential oil are separated, and the oil is gently moved into other containers, ready to be used as an essential oil. The water separated in this process is also useful and can be marketed as "flower water" (also known as hydrosol or sweet water) such as rose water, lavender water and citrus water. Water distillation can be carried out under reduced pressure (low vacuum) to lower the temperature and prevent it from exceeding 100°C, which is valuable for the protection of plant materials and essential oils. Thus, heat-sensitive neroli oil can be successfully extracted using this method.


If some plants cannot be soaked in hot water for a long time, such as lavender, it is necessary to find a more appropriate extraction method. Any plant material with high lipid content is not suitable for this extraction method, because long-term immersion in hot water will destroy the lipid material and synthesize it into alcohol and carboxylic acid.


2. Steam distillation


When steam distillation is used to extract and manufacture essential oils, plant material is placed in a still, and steam is injected into the plant material. The hot steam helps to release aromatic molecules from the plant material because the steam can force open the oil gland cells that store the essential oils in the plant material. These volatile essential oil molecules are released from the plant material into the steam.