Did you know that petroleum-derived hexane may be used to harvest your vegetable oil? No me neither but here’s how.


Vegetable oil comes from plant components, nuts, seeds, or fruits, but typically seeds.

Oil from plants is can be obtained either chemically with the use of solvents or mechanically (often called “crushing” or “pressing “).

Solvent extraction

Most commercially produced oils are solvent extracted. This involves a chemical solvent like the petroleum-derived hexane and heat up to 500 degrees. Once the oil is dissolved, the solvent is removed by distillation.

This technique is used for most of the “newer” oils such as soybean and cannola oils. Many of these products do not give up their oil easily, it has to be forced from them.

Hexane is a colorless flammable liquid, C6H14, derived from the fractional distillation of petroleum.

It is classified as an air pollutant by the Environmental Protection Agency (EPA) and as a neurotoxin by the Centers for Disease Control and Prevention (CDC).

It’s unclear how much hexane remains in the food after processing

Testing by Swiss scientists found no detectable levels but independent testing commissioned by the nonprofit Cornucopia Institute found hexane residues in soy oil.

The process recovers 99% of the oil but to get rid of the hexane, the oil is heated to a high temperature.

Also the high temperatures used in this process can and do change the chemical structure of oils. Many argue this reduces or even completely destroys the flavour of many delicate oils.


The oi is squeezed or pressed out of the vegetable matter in a variety of ways;

Screw press, a large screw based mechanism in a housing. As it turns it increases the pressure and  crushes the oils out of the seeds

Ram press uses  a  mechanise  piston in a cylinder that rams out the oil. Ram presses are generally more efficient than screw presses.


Industrial machines for extracting oil mechanically are call expellers.  They squeeze the oil out of the raw materials, under high pressure, in a single step. As the raw material is pressed, friction causes it to heat up and can sometimes exceed temperatures of 120°F (49°C). The amount of heat produced is important as heat can change the chemical structure of the oil.

Cold Pressed Oils

Cold pressing tries to avoid the problems of heat. In this process the nuts, seeds, or fruits from which the oil is being harvested are ground into an even paste.

This is slowly stirred till the oil to separates from the solids.Then pressure is applied,(either with a machine or in the traditional way, with a stone) forcing the oil out.

N.B The friction caused by the pressure will increase the temperature and manufacturers must keep it within a certain degree range to be able to claim that the oil is cold pressed. This varies the world over

European Union cold pressed oil must never exceeds a certain temperature which varies depending on the source material, but is usually between 80° to 120°F (27° to 49°C).

In the United States, labeling is not as regulated, so consumers generally need to contact companies directly to enquire as to their manufacturing process.

Many people believe that cold pressed oil has a superior flavor.


The extracted oil may now be purified, refined or chemically altered. More of that to come.


6 thoughts on “Petrol in my vegetable oil?

  1. I only get through one plastic bottle of milk a week. They get reused by the horticultural society for liquid feeds, and then by the plot holders for various uses.
    I don’t buy bottled water at all.
    As for shampoo, one small bottle lasts me just about for ever as I don’t have much hair!
    Thanks for another good informative entry! xx

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