If you go out into an olive grove, grab a handful of olives, and squeeze them hard, you will have an oily substance on your hand. But if you go out into a cornfield and grap a handful of corn kernals and squeeze them hard, you will have a milky, starchy paste in your hand, that isn’t oily at all. So how, exactly do they make corn (or other vegetable) oil? Moreover, is it something we should be consuming?
If you were pressing olives or coconut for their oils, you would put them into a device similar to a mortar and pestle to crush and press them, thereby extracting the oil. By this process doesn’t work for vegetables like corn. Prior to the 1960’s, corn oil was not produced. Vegetables just aren’t that oily. But with the invention of more powerful machinery and equipment, and advances in chemistry, new things became possible. What’s more, we’ve been told for the past 50+ years that vegetable oil is healthy for us.
To refine edible vegetable oil, the main steps include degumming, neutralizing, bleaching, deodorizing, winterizing (wax removal), fractionation, hydrogenation, and interesterification (Yes! That’s a real word the industry actually uses!).
To begin with, large machinery is used to harvest the corn and remove the kernals from the cobs. The removed product is called plant feedstock, and it must first be cleaned to address any foreign matters that might damage the production equipment. If you are wondering what foreign matters might be present in plant feedstock, you’re in good company. Apparently corn fibers, chunks of cob, husk particles, switchgrass, rotten vegetation, fungi, microorganisms, rocks and gravel, plastics, woody stalk particles, sludge, sharp objects, obvious pathogens, sand, silicate, unrelated solids and even decaying animal and insect remains can be present and must be washed and resized (but not removed).
Part of the cleaning process involves degumming, which reduces the phosphatides content in the crude products. Phosphatides are major components of cell membranes, consisting of glycerol and fatty acids. The product is then bleached to remove the naturally occurring variety of coloration. Once bleaching is completed, deodorizing occurs to remove the odor and taste that occurs under the high heat of the cleaning process.
Moisture in the plant feedstock has to be controlled to maximize efficiency of the production equipment as well, so it undergoes a process to add or remove moisture and adjust the particle size for proper cooking and flaking. The raw materials are cooked at a high temperature to regulate the moisture content of the particles, which, at this point in the process, are called grits (Not the same grits that southerners eat for breakfast!). Heated grits are flaked so that the cells are ruptured and oil is available for extraction.
Next a chemical extraction method is used that starts by adding solvents to the flaked grits. A solvent is a chemical that is added to ingredients to dissolve other substances. For example, water is a solvent for salt. That is, if you add salt crystals to water, the salt will dissolve in the water. Many chemicals can be used as solvents, such as acetone, methanol, chloroform, turpentine, hexane, and ethanol.
The most common solvent used for making vegetable oil is petroleum-derived hexane. This image of a hexane molecule shows the six carbons, connected by single bonds.
Hexane is a common constituent of gasoline, shoe glue, leather products, industrial cleaning products, and roofing materials. Hexane is produced by the refining of crude oil. The short term toxicity of hexane is fairly low, and produces a mild anesthetic effect (Ever felt sleepy after eating french fries?), but for applications such as pharmaceuticals, it is being phased out of usage due to its long term toxicity. Combustion of hexane gas can cause explosions and emissions are regulated by the EPA due to its carcinogenic (cancer causing) properties.
The flaked gits are conveyed through the extractor equipment while a mixture of hexane and miscella is sprayed countercurrently. Miscella is the industry term used to discribe the oil/solvent mixture leaving the extractor. It contains 70-80% solvent by weight. So the extractor equipment produces deoiled solids containing solvent and miscella.
The deoiled solids are then distilled under high heat to thermally separate the miscella into a liquid oil and solvent vapor. Detergent is added to help with the separation process. The solvent vapors are then vacuumed out, leaving behind the oil. The removed vapors are filtered to bring emissions to an acceptable level before being recycled back into the extractor.
Some oils have an unpleasant turbidity or cloudiness which is corrected by eliminating components like waxes that solidify at room temperature. Therefore, the oils undergo a process called winterizing which removes the wax and other substances that can cause turbidity. The oils are then neutralized to remove unpleasant odors and flavors caused by the solvents, detergents, and processing. It is critical for vegetable oils to be cleaned and deoderized, because potatoes and other vegetables will absorb these undesirable odors and flavors in the fryer.
Next they undergo fractionation, which separates the low and high melting point oils. High melting point oils remain mostly solid at room temperature, and are packaged into products like shortening and margarine, while low melting point oils remain mostly liquid at room temperature, and are marketed as cooking oil and nonstick sprays.
To increase the melting point of oil, for use in products such as margarine, the oil is hydrogenated. During hydrogenation, oils react with hydrogen gas using a nickel catalyst to speed up the reaction time. Using this process, unsaturated fats (liquids) can be converted into saturated fats (more solid). The oil is heated to a very high temperature, and a substance resembling water is shot into the oil molecules, altering the chemical bonds. Saturated fats occur naturally in substances like coconut oil, lard, and butter. Monounsaturated fats occur naturally in olive oil. Hydrogenated fats are unnatural and are known carcinogins (they cause cancer and are toxic to our health), but they proliferate the market because they are much cheaper to produce and the shelf life is about 10 years, compared to about 2 months for naturally occuring oils.
The final step is interesterification. This process modifies the melting point, slows rancidification, and makes the oil more suitable, taste wise, for deep frying, and is accomplished by moving fatty acids from one triglyceride molecule to another with the help of lipase enzymes as the catalysts. This process moves the fatty acids into a position that is easier to digest and metabolise, modifying the physical properties of the oil.
The finished oil is then packaged and labeled for consumer distribution.
In addition to the finished edible vegetable oil, a solid product (meal or cake) is also produced as part of the oil extraction process. This byproduct is a key component in animal feeds, once its been enhanced with protein and the fibre content has been minimized.
Additionally, used vegetable oil can be recycled into pet food, soap, detergent, cosmetics, and biodiesel and can also be used as a direct fuel in diesel engines (although it’s not recommended by the engine manufacturers or the automotive industry and may void your factory warranty).
So that’s how we get oil from vegetables.