Expeller pressed oil is any sort of oil that has been extracted from nuts, seeds, or other sources through a mechanical process that relies on sheer force rather than chemicals. In more ancient times, oil expulsion was done by hand, often with mallets or crank-style apparatuses. Most modern machines are far more advanced and are able to expel quite a lot of oil in not a lot of time. Using an expeller still tends to be less efficient than extracting oils through chemical means, but many people believe that it is healthier and more environmentally conscious to avoid harsh additives, particularly in oils designated for human consumption.
How the Expeller Works
The basic idea behind expeller pressed oil is to force oil out of something — usually a nut, a seed, or a vegetable like corn — without using anything but mechanical strength. Most expeller machines are set up so that the target item is placed between two heavy metal plates. When turned on, the machine will typically rotate those plates, progressively pressing the target harder and harder.
Any oil that is released during this process is caught in a runoff tray, where it is filtered and collected for later use. Small farms often employ single expellers in order to extract oil from crops. Larger manufacturing plants often have entire rooms or floors dedicated to expulsion, where multiple large machines are all operating at once.
Expeller pressed oil is usually rightly advertised as “all natural,” as the process involves no additives or additional ingredients. This often means that the oil is healthier — but the process is not always very efficient. Even the best modern machines are only able to extract about 75% of the oil from most sources, which necessarily means that there is some waste involved.
When it comes to nuts and seeds, the waste can often be used to make nut butters, or can be sold to snack food manufacturers to be used as a filler. Many vegetable “extras” are also of use in the pet food industry.
Why Chemical-Free Oil is Desirable
The precision of the expulsion process combined with the necessary waste means that expeller pressed oil is often more expensive than oils extracted with the help of certain chemicals. For many shoppers, however, the extra cost is worth the knowledge that no foreign substances have made their way into the finished product.
Hexane and Its Risks
Coating nuts and other food items in hexane or similar chemicals before attempting to extract their oils typically yields a much higher return rate. The compound causes most organic materials to quickly break down, which boosts yields well into the 90% range when it comes to oil recovery. The machines used for hexane extractions are usually slightly bigger than standard expellers, and often have specialized chambers for storing and administering the chemicals.
Environmentalists and health food advocates have a number of problems with hexane’s use in food preparation. Most oil manufactures use a number of different processing techniques to ensure that no residue makes its way into the finished product, but it can rarely guarantee purity. Even in trace amounts, the compound can have very serious health consequences.
Most of the risks come when hexane is inhaled, as can often happen when oils containing it are heated as they would be for frying or cooking. The chemical can cause sleepiness, nausea, and headaches. Chronic hexane inhalation may also result in cramping and muscle weakness or deterioration. These effects will often decline after exposure ends, but they are nevertheless concerning.
Comparison to Cold Pressed Oil
Expeller pressed oil is often very similar to cold pressed oil in that neither involves the use of any chemicals, though the processes involved in each are slightly different. Cold press methods also use an expeller machine, but only in a temperature-controlled setting. When the machine’s plates rotate and press the target object, a certain amount of heat is generated through friction, which the cold press method seeks to minimize.
Cold pressed oil is most common for things that have a very delicate flavor that can be disturbed by excessive exposure to heat. Certain extra virgin olive oils are made this way, as are many grapeseed extracts.