It can be extremely hard to know exactly what you're getting when it comes to oil. Oils are produced in many different ways: some might be extracted using solvents like hexane, and others are expeller pressed with a mechanical press that physically squeezes the oil out.
How oil is produced may not be clearly marked on a retail or bulk label, which makes things even more confusing. Sometimes descriptors about production methods can be found in the title, other times clues are left in an "abbreviated form", or the details may be found only in the description on a spec sheet. To make matters worse, some vendors make no mention at all on how the oil is made on any QA or Marketing documents, so you may just have to know what's "industry standard". This puts it in your hands to ask the right questions and get the proper documentation.
Centra Foods always tries to be as clear as possible. That's why, today, we will explain what the solvent extracting, expeller pressing, and cold pressing methods all look like in detail. When explaining these processes, we will be referring to canola oil specifically because it's one of the oils that is commonly expelled in all three variations. You will notice these processes are going to look very similar for many different type of other seed oils too, so you can apply these general ideas across the board with vegetable oils.
Solvent Extracting Process
Before oil can be taken out of the oilseed, the seed must first be ground up into a paste. Next, those seeds are washed or purged with a solvent, most commonly hexane, to release the fat. To remove the solvent from the oil, it is "flashed off" by heating it in a sealed chamber. The the solvent blend is heated to about 212°, distilling off the solvent and theoretically leaving virtually no detectable levels in the oil (if the proper techniques have been applied). Microscopic proportions of up to 25 parts per million of hexane can theoretically remain in the meal, which is a very high debate point in the natural food industry.
This oil extracted from the seed is known as crude (or unrefined) oil. The crude oil is then subject to the refining process, also known as the "RBD" process (refined, bleached, & deodorized). This process is what gives canola oil such a consistently light color and flavor. It is also a very similar process that is performed on many other vegetable oils such as soybean, sunflower, safflower, and refined olive oil. Some of these oils, including some canola, is also "winterized" or "degummed" as well.
Solvent expelling gets about 97-99% of the oil out of the seed, and is the most efficient way to get as much oil as possible out of each canola crush. That is one of the reasons that it is the cheapest option on the market.
Expeller Pressing Process
The expeller process uses a press to physically squeeze the oil out of the seed, rather than using chemicals. With this method, no solvents are used in the process, and therefore, the oil doesn't have a chance of having any hexane residue left over.
An expeller press is a screw-type machine which presses oil through a caged barrel-like-cavity using continuous pressure. The machine drives forward to squeeze the oil from the compressed/ground seeds. In this process, there is no added heat, but the pressure and friction involved may create natural heat in the range of 140° - 210°. Because of that, this process is technically not "cold pressed".
After all the oil is removed, the remaining solids left over are sold as meal for animal feed. Expeller pressing gets 87-95% of the oil out of the seed. This makes this option more expensive than the solvent expelled standard.
Expeller pressed oil is refined using the same process described above. This refining process involves additional heat from steam and use of a natural earthen bleaching clay.
Cold Pressing Process
Cold pressed oils must be produced below 122° (as legally defined in Europe). Cold pressing usually involves a low-resistance expeller press that is done at a very slow rate. This allows the process to avoid friction, and stay cooler. The production facility, depending on its location, may need to be kept at a lower temperature to help avoid bringing the seeds or oil to higher heat because of the surrounding atmosphere.
This "cold pressed" term should also only apply to fully unrefined oils that are not heated later during a refining process. When it comes to the term "cold pressed", it has at times been misused to describe expeller pressed oils, but these are really two different things.
Cold pressing process typically removes the least amount of the oil from the seed, making it the least efficient and more expensive for its process.
This cold pressed process, though it can be done on seed oils like canola oil, is more often seen in the production of virgin fruit oils like Extra Virgin Olive Oil, Extra Virgin Avocado Oil and Virgin Coconut Oil.
Which Oils Are The Most Common
In today's market, solvent expelled canola oil (and almost all vegetable oils) are the most common. Any oil that does not explicitly state "expeller pressed" or "cold pressed" on the bottle or in the ingredients listing can be assumed to be a solvent expelled oil.
The next most common oil would be expeller pressed, though the market share in comparison to solvent is still very small. It is more often seen with the non-GMO variety of seeds. You will also find it available in conventional (GMO) oils too. For example, you can find traditional GMO canola oil that is expeller pressed.
Cold pressed oils are most commonly seen the in the retail industry and often are sold as healthier non-GMO or organic varieties. The availability of cold pressed seed oils is often very small, and quite limited for bulk or foodservice use.
Topics: Comparing Oils