Refined vegetable oil starts from the seeds of various plant sources. The fats from plant seeds are polyunsaturated, meaning they remain in a fluid state at room temperature.
There are many different kinds of commercially refined vegetable-based oils, including canola or rapeseed oil, soybean oil, canola oil, corn oil, sunflower oil, safflower oil, and peanut oil.
The generic cooking term “vegetable oil” refers to a blend of a variety of oils often based on palm, corn, soybean or sunflower oils.
Refined cooking oils are made by highly intensive mechanical and chemical processes to extract the oil from the seeds. This process removes the natural nutrients from the seeds and creates a final product that oxidizes easily. The oxidation factor makes these oils more likely to break down into cancer-causing free radicals within the body.
In addition, many refined vegetable oils are also hydrogenated. This hydrogenation process makes them solid at room temperature so they can be sold as margarine and shortening. This hydrogenation process further damages the fatty acids in the oils, creating trans fatty acids, which are particularly dangerous to human health.
The consumption of vegetable oils created through chemical extraction processes is linked to widespread inflammation within the body, elevated blood triglycerides, and impaired insulin response. These oils have been linked to diabetes, cancer and heart disease in multiple studies.
The Process of Extracting Vegetable Oil
The process of extracting vegetable oil from oilseeds is not for the squeamish. Take a look at the steps and decide for yourself if this is a “food” you want to consume:
- Oilseeds such as soybean, rapeseed, cotton, sunflower are gathered. Most of these seeds are from plants that have been genetically engineered to resist the huge amounts of pesticides applied to them.
- The seeds are husked and cleaned of dirt and dust, then crushed.
- The crushed seeds are then heated to temperatures between 110 degrees and 180 degrees in a steam bath to start the oil extraction process.
- The seeds are put through a high volume press which uses high heat and friction to press the oil from the seed pulp.
- The seed pulp and oil are then put through a hexane solvent bath and steamed again to squeeze out more oil.Note: Hexane is produced by the refining of crude petroleum oil. It is a mild anesthetic. Inhalation of high concentrations produces first a state of mild euphoria, followed by sleepiness with headaches and nausea. Chronic intoxication from hexane has been observed in recreational solvent abusers and in workers in the shoe manufacturing, furniture restoration and automobile construction industries where hexane is used as a glue. The initial symptoms are tingling and cramps in the arms and legs, followed by general muscular weakness. In severe cases, atrophy of the skeletal muscles is observed, along with a loss of coordination and problems of vision. In 2001, the U.S. Environmental Protection Agency issued regulations on the control of emissions of hexane gas due to its potential carcinogenic properties and environmental concerns.
- Now the seed/oil mixture is put through a centrifuge and phosphate is added to begin the separation of the oil and seed residues.
- After solvent extraction, the crude oil is separated and the solvent is evaporated and recovered. The seed pulp residues are conditioned and reprocessed to make by-products such as animal feed.
- The crude vegetable oil is then put through further refining techniques including degumming, neutralization, and bleaching:
- Water degumming: In this process, water is added to the oil. After a certain reaction period, the hydrated phosphatides can be separated either by decantation (settling) or continuously by means of centrifuges. In this process step a large part of water-soluble and even a small proportion of the non-water-soluble phosphatides are removed. The extracted gums can be processed into lecithin for food, feed or for technical purposes.
- Neutralization: Any free fatty acids, phospholipids, pigments, and waxes in the extracted oil promote fat oxidation and lead to undesirable colors and odors in the final products. These impurities are removed by treating the oil with caustic soda (sodium hydroxide) or soda ash (sodium carbonate). The impurities settle to the bottom and are drawn off. The refined oils are lighter in color, less viscous, and more susceptible to oxidation. Hmmm, lucky for us.
- Bleaching: The major purpose of bleaching is the removal of off-colored materials in the oil. The heated oil is treated with various bleaching agents such as fuller’s earth, activated carbon, or activated clays. Many impurities, including chlorophyll and carotenoid pigments, are absorbed by this process and removed by filtration. However, bleaching also promotes fat oxidation since some natural antioxidants and nutrients are removed along with the impurities.
- Deodorization is the final step in the refining of vegetable oils. Pressurize steam at extremely high temps (500 degrees or more) is used to remove volatile compounds that would cause off-odors and tastes in the final product.The oil produced is referred to as “refined oil” and is ready to be consumed or for the manufacture of other products. A light solution of citric acid is often added during this step to inactivate any metals such as iron or copper present in the final product.
The process of refining vegetable oil damages the fats and makes the oils very unstable and prone to going rancid quite easily. Rancid oils in any form are particularly bad for your health because they introduce cancer-causing free radicals into your body, without the benefit of including an antioxidant like vitamin E.
Mary Enig and Sally Fallon of the Weston A. Price Foundation discuss this:
“High-temperature processing causes the weak carbon bonds of unsaturated fatty acids, especially triple unsaturated linolenic acid, to break apart, thereby creating dangerous free radicals. In addition, antioxidants, such as fat-soluble vitamin E, which protect the body from the ravages of free radicals, are neutralized or destroyed by high temperatures and pressures. BHT and BHA, both suspected of causing cancer and brain damage, are often added to these oils to replace vitamin E and other natural preservatives destroyed by heat.”
Try this Experiment
Here’s an experiment you can do to help you see what heat and light do to vegetable oil:
- Pour a 1/2 teaspoon of canola oil on one side of a metal cookie sheet.
- Pour a 1/2 teaspoon of olive oil on the other side of the cookie sheet.
- Bake the cookie sheet at 350 degrees F for about 30-45 minutes.
Notice how the end result is like sticky shellac? Imagine that stuck to the inside of your arteries.
Now do the same thing with bacon grease. See, no shellac. Just grease.
Resources for Further Reading
- History of Vegetable Oil A paper on the methods of vegetable oil extraction processes.
- The Lowdown on Edible Oils by the Lee Foundation for Nutritional Research, Milwaukee, Wisconsin
- The Facts About Fats by John Finnegan
- MadeHow article on the production of vegetable oil.
- Polyunsaturated Oils Promote Cancer
- Video Comparison of Making Butter to Making Canola Oil on Tom Naughton’s Fathead Movie blog. Compelling!