Contents
Methods of extracting a vegetable oil
Most vegetable oils come from oilseed fruits or seeds. In order to produce the “substantial oil”, the latter undergo a preparation: the leaves and stems are removed, the seeds are shelled and sometimes slightly heated in order to thin the oil and increase its yield.
By hydraulic press (with scroutins)
The dried fruits are cold pressed to provide an excellent quality virgin vegetable oil. The oils produced in this way are labeled “first cold pressing”: a preferred choice to guarantee healthy food and a process that respects nature.
By mechanical press (expeller)
The seeds are crushed and slightly heated. A pure oil is obtained devoid of any foreign substance and having retained the dietetic qualities of the seed. This is the most commonly used method.
By centrifugation (for oleaginous fruits)
This involves separating the oil from the pulp of the fruit (almonds, hazelnuts, walnuts).
By solvent extraction
Hexane (petroleum solvent) is intended to degrease the residue of crushed seeds. Then the distillation aims to remove the solvent in order to obtain the oil. If this method turns out to be the most profitable (because it makes it possible to harvest a much greater quantity of oil), it is nevertheless the least healthy since it is very likely that solvent residues are found in the oil thus obtained.
Precision: manufacturers are not obliged to mention the method of extraction. Consequently, the absence of a “solvent extraction” mention turns out to be an indicator of this mode of production.
Oil refining
Refining produces an oil without color or odor. This vegetable oil is found on supermarket shelves for common culinary use. But it is devoid of free fatty acids. There are 2 refining methods:
The physical method: in 5 steps
Acidification (by citric, phosphoric or sulfuric acid), centrifugation (aimed at removing mucilage), bleaching and filtration (by filtration on Fuller’s earth or activated carbon) then physical refining.
The soapstock method
Neutralization (with caustic soda), bleaching (with Fuller’s earth) then deodorization with water vapor.
For healthy use of vegetable oil, it is not recommended to use refined vegetable oil.