Dishrag Diaries

We’re finally back to continuing our series on FAT. Today I’d like to go over several modern methods of processing fat. (If you need to catch up, see here and here.)

Heat and Chemical Extraction

Extraction is used to remove (or extract) naturally occurring fats from fruits, nuts and seeds. Traditionally these fats were pressed from their sources by slow stone presses. But today, the name of the game is speed (and money, as in getting every last drop) and so big factories do it a bit differently…

Large oil production facilities crush the seeds (or nuts) and heat them to 230 degrees (F) to extract their oils. Then, to get the very last bit, they are pressed at pressures of ten to twenty tons per square inch, which generates further heat. Besides just the heat, the oils are also exposed to damaging light and oxygen. Even after all of this, there is still a small amount of oil remaining in the pulp of the seeds (about ten percent) and so they are subjected to chemical extraction using harsh solvents (usually hexane). Although the toxic solvent is then boiled off, up to 100 parts per million may remain in the oil. The solvent also retains any toxic pesticides adhering to the seeds before processing.

Expeller-Pressing

A sometimes safer form of extraction used today is expeller-pressing. This also involves crushing the nut or seed (generally in smaller batches) and is chemical-free.

If this process is done under low temperatures, with minimal exposure to light and oxygen, it can produce oils which can retain their freshness and nutrient value for years. However, the pressure required to press the nut or seed (which depends on the hardness of the nut or seed) produces friction, and therefore heat, which can prove damaging.

Cold-Pressing

Cold-pressing is a kind of expeller-pressing. No external heat is applied, and you would think that you could also assume from the name that any heat produced by the pressing friction would be monitored and limited. But, as with so many other labeling phrases, in the U.S. there is no standard for labeling an oil as “cold-pressed.” The manufacturer may decide for itself what the temperature threshold is for its “cold-pressed” oils. (For instance, Spectrum cold-pressed oils are expeller-pressed in a heat-controlled environment below 120 degrees.)

Hydrogenation

Remember how we discussed the reasons why polyunsaturated oils are liquid at room temperature? Hydrogenation seeks to turn those liquid oils into solids: margarine and shortening.

To do so, manufacturers start with either soy, corn, cottonseed or canola oils, extracted using heat and chemical extraction. (These are the cheapest oils and are almost always genetically modified.) These oils are then mixed with tiny metal particles, usually nickel oxide, used as a catalyst. In a high-temperature reactor, the oil/metal mixture is then combined with hydrogen under very high pressure. Soap-like emulsifiers and starch are pressed into the mixture to aid in forming the correct consistency. This product, as you can imagine, smells disgusting and looks like a gray blob. And so it is steam-cleaned (subjecting it again to very high temperatures) and then bleached. Finally, depending on the final product, dyes and flavorings are added and it is compressed into bars or tubs.

Now, to the naked eye, the process of hydrogenation is bad enough. But if you look at what’s happening on the cellular level, it’s far worse.

Think back one more time to when we touched on the cis formation in fatty acid chains. To review, polyunsaturated oils have many (hence, poly-) pairs of double carbon bonds, which causes the fatty acid chain to kink (making them liquid because the kinks prevent them from lining up nicely). These double bonds are on the same side of the chain as the chain’s hydrogen atom pairs, and this is called the cis formation, most often found in nature. When that same oil is subjected to the heat and nickel catalyst of hydrogenation, one of the hydrogen pair’s atoms changes position on the fatty acid chain. It moves to the other side, causing the molecule to straighten (and hence line up nicely, making the oil solid). This formation is called the trans formation, and is rarely found in nature. Whether you know it or not, you’ve probably heard quite a bit about fatty acid chains that make that tiny change; they are called trans fats. (Ahhhhh! Now you know why I’m telling all this!)

OK, we’re almost there. We’ll round out the fat series by talking about the effects that different types of fats have on our bodies, and what kinds we should eat, limit or avoid. Thanks for sticking with me!

You may also like:

The Skinny on Fats: Mono-, Poly-, Un-, Saturated. What Does it All Mean?
The Skinny on Fats: Short-, Medium-, Long-Chain Fatty Acids. What Does it All Mean?

For further study:

Know Your Fats by Mary Enig
The Oiling of America (DVD)
Nourishing Traditions by Sally Fallon Morell

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