When selecting edible oil, many consumers use pressing and extraction as a standard to distinguish the quality of edible oil. They believe that pressed oil is produced by mechanical methods while extracted oil is produced with the addition of chemical solvents, and the former is safer to consume.
This is not the case. Recent tests by the food hygiene department show that due to the limitations of the process, edible vegetable oils produced by the pressing method often lag behind those produced by the extraction method in key indicators.
Experts point out that the factors affecting the quality of edible oil are not the production process, but the degree of refining and whether the production process strictly follows operational standards.
Pressing and extraction are the two main production processes for edible vegetable oil. The pressing method uses mechanical means to squeeze the oil out of the raw material, while the extraction method uses No. 6 solvent oil to dissolve the oil in the raw material, creating a mixed oil, and then vaporizes the solvent oil in the mixed oil to separate it from the oil.
Oils produced by either the pressing or extraction method are called crude oil, which contains more protein, gum, free fatty acids, pigments, and other substances, and cannot be consumed directly. They all need to undergo processes such as water washing, alkali washing, deacidification, decolorization, and deodorization to become lighter in color and clear refined oil.
Compared to the pressing method, a very ancient production method, the extraction method for oil production was not developed until 1870 in Germany. However, due to its high oil yield, controllable operational procedures, and suitability for large-scale production, it has become a world-recognized advanced oil production technology. Currently, over 90% of oilseeds in developed countries and over 80% of oilseeds in China use the extraction method to produce crude oil, which is then refined into qualified edible vegetable oil.
Taking soybean oil production as an example, its process is as follows: first, the soybeans are screened, cleaned, crushed, softened, and rolled into flakes. Then they enter an extraction device and undergo multi-stage immersion with No. 6 solvent oil to dissolve the oil. The solvent oil is then evaporated and distilled to produce crude extracted oil. The crude oil then undergoes multiple processes to remove residual solvents and other impurities, turning it into a pure, clear product that meets national edible oil quality standards.
Of course, edible vegetable oils produced by the extraction process may have excessive residual solvents in the final product if the "solvent removal process" is not strictly followed during refining. Consuming oil with excessive solvent residues can irritate and damage the human nervous system and organs. Related link: Three indicators determine the quality of oil
Three indicators—acid value, peroxide value, and residual solvent content in extracted oil—are the core of edible vegetable oil product quality and reflect the control of the processing technology, product quality, degree of oil decomposition, and oxidation or deterioration. The higher the acid value and peroxide value of the oil, the lower its quality.
Exceeding the standard for acid value, peroxide value, and residual solvent content in extracted oil usually has two causes: one is substandard processing during oil production, and the other is improper packaging or storage leading to oxidation or hydrolysis reactions.
Long-term consumption of rancid and spoiled oil can lead to a deficiency of essential fatty acids, resulting in nutritional deficiencies and metabolic developmental disorders. In severe cases, symptoms such as dizziness, vomiting, abdominal pain, bloating, and diarrhea may occur. Related link: How to choose edible vegetable oil
One, national standards classify edible vegetable oils into four grades, with Grade 1 being the highest quality. When buying edible oil, carefully check the label and try to buy edible vegetable oil with a high quality grade and a recent production date. If the outer packaging of the edible oil does not specify the grade (blended oils do not have a grade), production process, etc., as required by national standards, do not purchase it.
Two, carefully inspect the appearance of the edible oil. High-quality edible oil is light in color, not turbid, and free of sediment and suspended substances, with a lower viscosity. If the oil contains too much water, has rancidified, or has been adulterated, it will become turbid and less transparent.
Three, if the edible oil's label states that vitamin E or other antioxidants have been added, this oil is less prone to rancidity. Four, be cautious when purchasing bulk edible vegetable oil.