Traditional pressing methods struggle to fully preserve sesame oil’s aroma. However, utilizing supercritical fluid technology enables the production of more fragrant and fresher sesame oil. Let’s explore how this innovative extraction method transforms sesame oil’s quality.
Anyone who’s visited a traditional market has likely paused at least once, drawn by the savory aroma of sesame oil wafting from a mill or rice cake shop. The fragrance of freshly pressed sesame oil, made by roasting sesame seeds and pressing them in an oil press, is so intensely savory it can be almost intoxicating. But in truth, that rich aroma wafting from the mill is actually the “discarded” fragrance components that never fully dissolved into the sesame oil and instead evaporated into the air. This loss of aroma was unavoidable during the mechanical pressing process.
This issue of aroma loss in sesame oil connects to a common everyday experience many people have. When cooking with sesame oil at home, we often anticipate that rich, nutty aroma, yet the oil often fails to deliver the expected flavor once added to the dish. This is because most of the aroma is lost during the mechanical extraction process. This problem has also been a major concern for chefs who frequently use sesame oil.
So, is there a way to extract sesame oil without this loss of aroma? The answer lies in “supercritical fluid.” Water becomes ice when its temperature drops below freezing and turns into steam when boiled, which then evaporates. Thus, matter can exist in solid, liquid, or gaseous states. Supercritical fluid refers to yet another state that doesn’t belong to any of these. Imagine heating a liquid, trapping the evaporated gas in a sealed container, and continuously increasing both temperature and pressure. As pressure rises, the distance between gas molecules becomes as close as in a liquid, but the high temperature prevents it from becoming liquid. When temperature and pressure exceed a certain “critical point,” the substance enters this intermediate state—neither liquid nor gas—known as a supercritical fluid.
Supercritical fluids possess the properties of both liquids and gases simultaneously. First, due to the extremely high pressure, they have a density nearly approaching that of a liquid. Generally, higher density allows for better solubility in dissolving other solids or liquids, and supercritical fluids exhibit this property of high solubility. However, they also possess diffusion properties comparable to gases, enabling rapid penetration into every corner of confined spaces.
These characteristics of supercritical fluids offer significant application potential in chemistry and biology. For instance, in the medical industry, supercritical fluids play a crucial role in the extraction and purification processes of specific drugs. Additionally, in environmental science, supercritical fluids are widely used for pollutant removal and in environmentally friendly extraction processes. The versatile properties of supercritical fluids, useful in so many areas, can also provide an innovative method for extracting sesame oil.
So, how exactly does one use this supercritical fluid to extract sesame oil? Supercritical fluids are applied in various fields due to their unique properties mentioned above, one of which is extraction technology using supercritical fluids. By adding a chemical substance called a cosolvent to the supercritical fluid, it becomes possible to selectively dissolve only the desired target substance, depending on the type and amount of the cosolvent. Its high diffusivity, permeability, solubility, and selective dissolution capability allow for the extraction of only specific desired substances from natural materials. Furthermore, after extraction, simply adjusting the temperature and pressure to return the supercritical fluid to its gaseous state facilitates easy separation from the extract. This gas-phase solvent can then be reprocessed under appropriate temperature and pressure to restore its supercritical state for reuse in the extraction process, making it both economical and environmentally friendly. The most commonly used solvent in supercritical fluid extraction is carbon dioxide, which is also employed in the sesame oil extraction process. Carbon dioxide has a relatively low critical temperature of about 31°C, making it safe as it causes no damage to natural materials and is non-toxic. Furthermore, it is readily available and inexpensive, as it is a byproduct of various chemical processes.
Now, let’s step inside a factory producing sesame oil using supercritical extraction technology. First, roasted sesame seeds are placed into the extractor. Next, carbon dioxide, pretreated to reach a supercritical state, is introduced into the completely sealed extractor. The supercritical carbon dioxide permeates the minute pores on the sesame seed surface, extracting the oil components. This supercritical carbon dioxide, now containing sesame oil, passes through a separator where it reverts to a gas. As it loses its solubility for sesame oil, it separates from the oil. The extracted sesame oil is aged and then packaged. The separated carbon dioxide re-enters the pretreatment process, returning to its supercritical state to cycle through the entire process again.
Sesame oil extracted using supercritical carbon dioxide offers significant advantages over oil extracted by conventional mechanical pressing. Due to the nature of supercritical fluids, which require temperatures and pressures above their critical point, the entire process occurs in a sealed environment. This results in superior preservation of the sesame oil’s flavor and aroma compared to open-press extraction methods. Furthermore, the mechanical pressing process compensates for this loss of aroma by roasting sesame seeds at high temperatures to enhance their flavor. However, during this process, some seeds burn, creating carbonized substances that contaminate the oil and cause a bitter aftertaste. In contrast, the supercritical extraction process incurs no loss of flavor or aroma. Therefore, sesame seeds are not roasted at high temperatures, eliminating the risk of carbonized substances forming and minimizing nutrient degradation in the seeds. Other advantages over conventional processes include the absence of sesame residue contamination in the oil and the ability to extract most nutrients, such as tocopherols, alongside the oil components.
Beyond sesame oil, supercritical extraction is widely applied across diverse industries. It is used in the caffeine extraction process for decaffeinated coffee, in extracting resin from hops (used in beer production), and in separating nicotine from tobacco. Its applications span everyday foods and beverages to high-value-added sectors like natural medicinal ingredients, cosmetic raw materials, and flavorings. Compared to conventional extraction processes that used environmentally harmful or toxic organic solvents, supercritical extraction is safe, clean, and economical due to its reusability. Supercritical extraction is expected to find diverse applications in the food and pharmaceutical sectors going forward.
Its potential applications in the food industry are limitless. Supercritical fluid extraction technology can significantly enhance the quality of health supplements, natural spices, and various food ingredients. Particularly as consumers increasingly pursue healthier diets, the importance of natural ingredients is growing. Supercritical extraction is gaining attention as an eco-friendly and effective method. We look forward to seeing what innovations this technology will bring and what changes it will make to our dining tables.
