Oil Extraction Methods
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The first and oldest method is pressing, whether by hand, mechanical or hydraulic means. Pressing yields the best quality oil. Only Sesame Seeds (and Olives) yield enough oil to be processed with pressing alone. Beware of unscrupulous manufacturers who try to pass any other kind of oil, besides Sesame or Olive, off as Cold Pressed OilWith, hand, mechanical or hydraulically pressed oils labeled "cold pressed" or "pressed", you can should expect to be purchasing crude or unrefined oil.

Varieties

Expeller Pressed

The second method of extraction is Expeller Pressed, which uses a screw-like, rotating worm shaft to put the organic material under pressure to squeeze out the oils. Temperatures over 120° F (49°C), and between 200° & 250° F (93° to 121° C) are usual in expeller pressing, which disqualifies it as a cold-press method. Very little expeller-pressed oil is left unrefined. Most is further refined. If you are particular about the oil you are buying, you will want to find out more than just if it is expeller pressed. You will want to also know if it is unrefined (also called “crude”) or refined so that you know what you are paying for and working with.

Solvent Extraction

Solvent Extraction is the most affordable method of processing oils in large quantities. Unfortunately, it also yields the least healthful and flavorful end product. In Solvent Extraction, oil bearing product is ground, then steam cooked and mixed with Hexane, a chemical solvent, to strip the maximum amount of oil from the seeds or grains. The oil is then filtered to remove impurities that lower the smoke point, and finally bleached to a light color and deodorized to leave it nearly scent-free. Solvent Extraction is the process used by most big commercial oil producers. About 98% of the soy oil in the U.S., for example, is solvent extracted. The food oil and grocery industries call these mass-market products “RBD” oils: refined, bleached, and deodorized.

Nutrition

Refined and Unrefined oils of the same variety contain similar fatty acid compositions, but the higher processing temperatures (over 180˚F) for refined oils can damage the Essential Fatty Acids, and create free radicals that can be a health concern. Furthermore, unrefined oils contain more vitamin E, chlorophyll and phytosterols than refined oils. Unrefined safflower, sunflower, and corn oil contain the highest amounts of vitamin E, followed by sesame, soybean, peanut and lastly olive oil.