Essential oils have been used for hundreds of years to enhance health, beauty, and wellness naturally and holistically—no surprise considering how good they can be for your mind and body. People use essential oils to relieve stress and pain, fight the flu, reduce inflammation, prevent infection, soothe irritated skin, relax the mind, energize the body, normalize hormones, regulate digestion, and improve mental clarity.
What is essential oils?
Essential oils are concentrated hydrophobic liquids containing volatile aromatic compounds from plants. Essential oils are also known as volatile oils, ethereal oils, ether oils, or simply the “oils” of the plants from which they are extracted, such as clove oil. Oil is “essential” because it contains the “essence” of botanical scents – the characteristic scent of plants, which comes from rosemary, lavender, juniper and tea tree oils as well as seed oils such as almond oil, walnut oil, olive oil and almond oil etc.
How to extract essential oils?
After the plant is harvested, the extraction step needs to be carried out immediately to avoid the loss of the aromatic compounds of the plant. The essential oil is extracted from various parts of the plant, including leaves, flowers, peels, seeds, roots, and bark, The common extraction methods are as follows: distillation, cold pressed, liposuction, immersion solvent extraction, and supercritical extraction.
Most of the essential oils are extracted by distillation, and most of the citrus essential oils are extracted by cold pressed. The more popular essential oil extraction method is supercritical CO2 extraction. So what are the characteristics of CO2 and cold pressed extraction?
What is cold pressed process?
Cold-pressed oils are the go-to when considering essential oils, and even cooking oils actually are, although it’s still theory and debate.
It is worth noting that the concept of cold pressing does not mean a low-temperature environment, but a lower operating temperature (40-60°C) compared to general high-temperature extraction. While this ancient technique is effective, it is also labor-intensive.
Cold pressed edible oil process
The traditional process of cold pressing to extract edible oil is that the raw material is usually ground into a paste and pressed with a heavy stone mill, turned by an ox cart until it drains the oil. However, with the advancement of technology, now, machines are used. Presses come in a variety of sizes, from small ones for domestic use to large commercial presses for cooking oil extraction. Seeds are placed into cylinders containing rotating screws. The screw grinds and crushes the seeds until the oil is extracted. Small holes in the bottom of the cylinder allow oil to flow into a collection container. While some heat is generated through friction as the screw breaks down the seeds, there is usually not enough heat to damage the oil.
Cold pressed essential oil process
Unlike distillation, which requires still, the cold pressed essential oil can be handcrafted using centuries-old techniques. In ancient times, the peel of the fruit was soaked in warm water to help loosen the juice and make it more receptive to the pressing process. The peel is then pressed using a sponge and the oil is extracted from the peel. Once the sponge is filled with the extracted oil from the peel, it is emptied into a collection container where it will sit to allow the oil and juice to separate properly. Then, the cold-pressed essential oils will be pumped away.
Today, cold pressing is less labor-intensive. Place plants and plant parts (such as fruit peels) into a container with spikes and pierce slowly. Most modern cold presses also utilize centrifugal force to help separate the oil from the rest of the mill pulp and liquid. The piercing and spinning process releases the essential oils, which are then collected, bottled, It is worth noting that the concept of cold pressing does not mean a low-temperature environment, but a lower operating temperature (40-60°C) compared to general high-temperature extraction. While this ancient technique is effective, it is also labor-intensive.
Which essential oils are extracted by cold pressed?
The cold pressing method is used for citrus essential oils or base oils. The peel or pulp is pressed, and water is added to the juice. Finally, the essential oil is separated from the juice (water layer) by centrifugal force. For example sweet orange, grapefruit, tangerine, lemon, lime essential oil, etc.
And use in pure form or add to other products, especially carrier oils like jojoba or argan oil.
Supercritical CO2 fluid
There are three phases of any substance – gas phase, liquid phase, and solid phase. The point where the three phases coexist in equilibrium is called the triple point. The point at which the liquid and gas phases are in equilibrium is called the “critical point”. The temperature and pressure at the critical point are called critical pressure and critical temperature. Different substances require different pressures and temperatures for their critical point.
SCF in supercritical fluid (SCF) technology refers to a fluid whose temperature and pressure are both higher than the critical point. Such as carbon dioxide, ammonia, ethylene, propane, propylene, water, etc. The state above the critical temperature and critical pressure and close to the critical point is called the “supercritical” state. In the supercritical state, the properties of the gas and liquid phases are so similar that they cannot be distinguished, so it is called SCF.
Supercritical CO2 Fluid Extraction and Separation Process
The extraction and separation process of supercritical CO2 fluid is carried out by using the relationship between the dissolving ability of supercritical CO2 fluid and its density, that is, using the influence of pressure and temperature on the dissolving ability of supercritical CO2 fluid.
When CO2 is in a supercritical state, it becomes a single-phase state with properties between liquid and gas. It has a density and viscosity similar to that of liquid, although it is higher than that of CO2 gas but significantly lower than that of liquid. The diffusion coefficient is 10-100 times that of liquid. Therefore, it has good permeability and strong dissolving ability to the material, and can extract the required components from the material.
In the supercritical state of CO2, the supercritical CO2 fluid is contacted with the substance to be separated, so that it can selectively extract the components with large polarity, small polarity, high boiling point, low molecular weight and large and small molecular weight.
In addition, the density and dielectric constant of supercritical CO2 fluid increase with the increase of the pressure of the closed system, and the polarity increases, and the components of different polarities can be extracted step by step by using the program boosting.
Of course, the extract obtained corresponding to each pressure range cannot be single, but the optimal proportion of mixed components can be obtained by controlling the conditions, and then the supercritical flow CO2 can be changed into ordinary CO2 gas by means of decompression and temperature increase. The extracted substances are automatically completely or basically precipitated, so as to achieve the purpose of separation and purification, and combine the two processes of extraction and separation into one, which is the basic principle of supercritical CO2 fluid extraction and separation.
Two types of supercritical CO2 extraction machine
- Research and analysis type, mainly used in the analysis of small quantities of substances, or to provide data for production.
- Preparation production type, mainly used in batch or mass production.
Composition of supercritical CO2 extraction machine
The supercritical CO2 extraction machine can be functionally divided into eight blocks:
- Extractant supply system,
- Low temperature system
- High pressure system
- Extraction system
- Separation system
- Modifier Supply System
- Circulatory system
- Computer control system.
CO2 extraction equipment specifically includes carbon dioxide injection motor, extractor, separator, compressor, carbon dioxide storage tank, chiller and other equipment.
Six benefits of supercritical CO₂ extraction
No residual toxic solvents
Supercritical carbon dioxide extraction mainly uses carbon dioxide to replace traditional solvents for extraction. Since carbon dioxide itself is non-toxic, there is no problem of solvent residues, and the pollution to the human body and the environment can be reduced to zero.
No thermal degradation
The traditional solvent extraction uses a high extraction temperature, which causes obvious damage to some active ingredients such as antioxidants, which is the so-called thermal degradation phenomenon. Because the extraction temperature used in supercritical CO₂ extraction is generally 35~36 ℃, Therefore, using a lower temperature process can completely and effectively extract the antioxidant active ingredients.
Long product shelf life
Because supercritical CO₂ itself has the effect of sterilization, and the whole extraction process is a closed process, the products after supercritical CO₂ extraction can prolong their shelf life of the products.
High product purity; light and transparent color
The color of the extract extracted by supercritical carbon dioxide is usually more transparent than that of ordinary extracted products. Because supercritical carbon dioxide itself has the function of concentration, it can effectively improve the purity of the product.
Use safe and non-explosive solvents
Since CO₂ gas itself is a non-explosive substance, it is very safe to use in manufacturing. In general, traditional solvent extraction can choose different types of solvents, and can also be adjusted by temperature; while supercritical fluid extraction adjusts the properties of the solvent by temperature and pressure, and an additional operating variable is added to the operating variable to adjust the properties of the solvent. Can increase the selectivity of extraction.
Low-energy solvent recovery and regeneration process
Supercritical fluid extraction equipment has the function of “carbon dioxide recovery”, and only uses low energy consumption to achieve the purpose of solvent recovery and reprocessing, which can be described as “green environmental protection high-tech”.
What substances can be extracted use supercritical CO2?
Because carbon dioxide is non-polar, it is especially suitable for fat-soluble extracts in the selection of extraction targets.
Five types fat-soluble extracts
- Capsanthin and lutein in natural pigments, β-carotene, and lycopene in spirulina.
- Extracting red pepper, in addition to the natural red pigment, can also obtain capsaicin, which is an effective ingredient for anti-tumor and analgesia;
- Carotenoids in chrysanthemum and calendula can be widely used in food, cosmetics, and feed additive industries;
- Spirulina contains A large amount of beta-carotene is an excellent raw material for fighting free radicals;
- Lycopene in tomatoes, it is a very strong antioxidant.
In addition, natural fragrances are not easy to be synthesized artificially because of their unique, comfortable, and natural aroma. The high-efficiency supercritical fluid extraction method is different from the traditional squeezing method, steam distillation method, volatile solvent stripping, or adsorption method, and can be applied to celery seed, ginger oil, citronella oil, fennel oil, orange blossom fragrance, osmanthus, angelica essential oil, citrus essential oil, etc. extraction or concentration.
Health-care edible oils
In terms of health-care edible oils, because most plant seeds contain a large amount of oil, they are traditionally extracted by pressing or solvent, but they still cannot get rid of the major defects of low oil yield and organic solvent residues. If the supercritical fluid is used to extract soybean, peanut, rice bran, wheat germ, pumpkin seed, grape seed, sunflower seed, or corn germ, in addition to improving the yield of oil and fat, it is easier to separate directly from carbon dioxide and saves the need for vacuum distillation and purification. The trouble of separation can save energy. It is worth mentioning that in the extraction of hops required for brewing beer, the α-acid yield obtained by supercritical fluid extraction is much higher than that of traditional organic solvent extraction. In recent years, it has been used in Germany, the United States, New Zealand, and other countries’ commercial processes.
CO2 vs cold pressed extraction: 7 features compared
Flavor aroma and nutritional value
The CO2 extraction process can first extract terpenes in a subcritical state, and then extract essential oils in a supercritical state, which will effectively retain all the flavor, aroma and nutritional value of the plant.
Cold-pressed essential oils retain all the flavor aroma and nutritional value of plants: making these oils ideal for all culinary and skin care requirements, cold-pressed essential oils contain zero grams of trans fatty acids and are naturally cholesterol-free.
Supercritical CO2 extraction Due to its unique process, supercritical fluid extracts the oil and fat in the biomass, which is an impossible task for the cold-pressed extraction process.
Cold-pressed preservation of natural ingredients: This traditional method is a mechanical process that uses neither heat nor chemicals as preservatives, so the oil retains its original chemical structure.
The supercritical CO2 extraction process is also a low temperature extraction process, again without the use of chemicals.
However, the cold pressing process has no selective extraction, while the supercritical CO2 extraction can be selectively extracted by adjusting the temperature and pressure. The supercritical CO2 essential oil is often light yellow and does not contain other impurities (ineffective substances).
Rich in Antioxidants: Cold-pressed oils are rich in antioxidants, which have many health and skin benefits in addition to preventing free radical damage.
It has been concluded in many published papers that supercritical CO2 essential oil is also rich in antioxidants, such as rosemary antioxidants and essential oils, Taiwan five leaf pine, essential oils from citronella.
Cold-pressed oils are chemical free: they are processed without chemical extraction, without solvents such as hexane, without preservatives, without additives, and with 100% natural content.
Supercritical CO2 extraction also does not use chemical extraction, CO2 is colorless, odorless, and can be easily and completely removed by releasing the pressure in the extraction chamber. It’s what we exhale and is needed for plant growth, which means it’s harmless to use in the extraction process. The absence of potentially harmful solvents in the extraction of carbon dioxide means that neither the human body nor the environment is contaminated.
The difference between cold-pressed oil and supercritical CO2 essential oil is that cold-pressed oil will retain heavy metals in biomass, while the essential oil extracted by supercritical CO2 fractionation process will not contain heavy metals.
These two essential oils also have a disadvantage: the residues of plasticizers must be removed by other special processes, such as molecular distillation.
Essential oils that go through the cold-pressing process come mainly from citrus fruits.
Supercritical CO2 extraction deals with all fat-soluble substances. Supercritical CO2 extraction is more widely used than cold pressing.
High investment is the biggest disadvantage of supercritical CO2 extraction.
Who is better?
Comparison of these two processes, when you only need to extract essential oils from citrus fruits, our suggestion is that you can choose the cold-pressed process because it really requires less investment.
If you need more varieties of essential oils, you still need to choose another process, such as supercritical CO2 extraction. After all, it’s impossible to sell only citrus essential oils in a store.