Vegetable oils: the truth about the method of their extraction
Ever since animal fat was falsely linked to heart disease in the 1950s, vegetable oil consumption has skyrocketed worldwide.
Ironically, vegetable oils didn't resolve the phenomenal rise in heart disease as it continues to be the number one cause of death around the world.
What are vegetable oils and how are they manufactured?
Vegetable oils, such as sunflower, corn, soybean, etc., are mostly extracted from seeds, nuts, cereals and grains. You might think that oil manufacturers take the seeds, press them and voila la, you get the oil from the other side of the machine.
Unfortunately, this is far from the reality. Solvent extraction is the most commonly used method for vegetable oil extraction as it helps extract up to 99% of the oil content in a seed or cereal. These are the steps by which seeds, such as sunflower seeds, are turned into oil:
- Cleaning and de-hulling of the seeds
The harvested seeds are passed over magnets and sieves to get rid of any traces of metals and other impurities. Then the seeds are cracked and de-hulled.
- Grinding the seeds
The seeds are ground into uniform fine particles in order to increase the contact area of the material with the solvent resulting in maximum oil yield. Some processes may involve cooking the flaked material to denature cell tissues for easy penetration of the solvent.
- Pressing and solvent extraction
The cooked flaked material is pressed through a slotted barrel to squeeze out some of the oil. However, in order to get the maximum yield of oil, the flaked material is then treated with a solvent, which dissolves the remaining oil out of it. The most commonly used solvent in the oil industry is hexane, which is extracted from petroleum.
- Removing the solvent from the solvent-oil mixture
The solvent is separated from the oil through distillation. The process involves heating the resulting solvent-oil mixture (miscella) in evaporators at 80°C. Further, steam is injected on the shell side to vaporize and reduce the solvent to about 5% of the oil. Finally, the mixture is subjected into steam-stripping in a vacuum tower to remove the remaining solvent, at temperatures rising to a final of 110°.
- Oil purification and refining
Once the oil has been extracted, a process of purification takes places to remove any impurities that may still be present after the extraction process. This is an important step as these impurities can affect the taste, quality and clarity of the final oil product.
Refining is the final processing step when it comes to creating vegetable oil. The refining process removes any missed impurities and other remaining undesired constituents, through bleaching and deodorizing steps.
During bleaching, the oil is heated and mixed with lye (caustic soda) to eliminate the chemical taste. The oil is then steamed and heated under vacuum to 200 – 280°C to remove the caustic soda taste. Once this step has been completed, the oil is ready for packaging.
Would you still consider vegetable oils as a healthy option?