Vegetable oil

Vegetable oil or vegoil is fat extracted from plant sources, known as oil plants. Although in principle other parts of plants may yield oil, in practice seeds form the almost exclusive source. Vegetable oils are used as cooking oils and for industrial uses. Some types, such as cottonseed oil, castor oil and some types of rapeseed oil, are not fit for human consumption without further processing.

Like all fats, vegetable oils are esters of glycerin and a varying blend of fatty acids, and are insoluble in water but soluble in organic solvents.

Sources of Vegetable Oil

Common sources of vegetable oil include:

Oilseeds:

Other vegetable oils:

According to the USDA, the total world consumption of major vegetable oils in 2000 was:

Oil source World consumption
(Millions of metric tons)
Soybeans 26.0 MMT
Palm 23.3 MMT
Rapeseed 13.1 MMT
Sunflowerseed 8.6 MMT
Peanut 4.2 MMT
Cottonseed 3.6 MMT
Palm Kernel 2.7 MMT
Olive 2.5 MMT

Note that these figures include industrial and animal feed use. The majority of European rapeseed oil production is used to produce biodiesel, or used directly as fuel in diesel cars which may require modification to heat the oil to reduce its higher viscosity. The suitability of the fuel should come as little surprise, as Rudolph Diesel originally designed his engine to run on peanut oil.

Extraction

  • The "modern" way of processing vegetable oil is by chemical extraction, using solvent extracts, which produces higher yields and is quicker and less expensive. The most common solvent is petroleum-derived hexane. This technique is used for most of the "newer" industrial oils such as soybean and corn oils.
  • Another way is "physical extraction," which does not use solvent extracts. It is made the "traditional" way using several different types of mechanical extraction. This method is typically used to produce the more traditional oils (e.g., olive, coconut and palm oils), and it is preferred by most "health-food" customers in the USA and in Europe. Expeller-pressed extraction is one type, and there are two other types that are both oil presses: the screw press and the ram press.

Production of Edible Oil

Neither the oil nor the meal is considered edible immediately upon crushing the bean and extracting the crude vegetable oil. Animals fed raw meal will waste away, even though soy meal is high in protein. Researchers at Central Soya discovered that a trypsin inhibitor in soybeans could be deactivated by toasting the meal, and both licensed their invention, and sold soy meal augmented with vitamins and minerals as MasterMix, a product for farmers to mix with their own grain to product a high quality feed.

Crude soybean oil is first mixed with caustic soda. Saponification turns free fatty acids into soap. The soap is removed with a centrifuge and disposed of, typically as an low quality ingredient for animal feed. The remaining oil is deodorized by heating under a near-perfect vacuum and sparged with water. The condensate is further processed to become vitamin E food supplement, while the oil can be sold to manufacturers and consumers at this point.

Some of the oil is further processed. By carefully filtering the oil at near-freezing temperatures, "winter oil" is produced. This oil is sold to manufacturers of salad dressings, so that the dressings do not turn cloudy when refrigerated.

The oil may be partially hydrogenated to produce various ingredient oils. Lightly hydrogenated oils have very similar physical characteristics to regular soy oil, but are more resistant to becoming rancid.

Margarine oils need to be mostly solid at 90F so that the margarine does not melt in warm rooms, yet it needs to be completely liquid at 98F, so that it doesn't leave a "lardy" taste in the mouth.

Another major use of soy oil is for fry oils. These oils require substantial hydrogenation to keep the polyunsaturates of soy oil from becoming rancid.

Hardening vegetable oil is done by raising a blend of vegetable oil and a catalyst in near-vacuum to very high temperatures, and introducing hydrogen. This causes the carbon atoms of the oil to break double-bonds with other carbons, each carbon forming a new single-bond with a hydrogen atom. Adding these hydrogen atoms to the oil makes it more solid, raises the smoke point, and makes the oil more stable.

Hydrogenated vegetable oils differ in two ways from other oils which are equally saturated. During hydrogenation, it is easier for hydrogen to come into contact with the fatty acids on the end of the trigylceride, and less easy for them to come into contact with the center fatty acid. This makes the resulting fat more brittle than a tropical oil; soy margarines are less "spreadable".

The other difference is that trans fatty acids are formed in the hydrogenation reactor. Trans acids are increasingly thought to be unhealthful.

History of Vegetable Oils in the US

While olive oil and other pressed oils have been around for millenia, Procter & Gamble researchers were innovators when they started selling cottonseed oil as a creamed shortening, in 1911. Ginning mills were happy to have someone haul away the cotton seeds. P&G researchers learned how to extract the oil, refine it, harden it, and package it as a creamed shortening. Compared to the lard they were already selling to consumers, Crisco was cheaper, easier to stir into a recipe, and could be stored at room temperature for two years. (P&G sold their Crisco and Jif peanut butter lines to JM Smucker in 2002.)

Soybeans were an exciting new crop from China in the 1930s. Henry Ford built a car almost entirely out of soybean-derived plastics. Roger Drackett had a successful new product with Windex, but he invested heavily in soybean research, seeing it as wise move. By the 1950s and 1960s, soybean oil became the most popular vegetable oil in the US.

In the mid-1970s, Canadian researchers developed a low-ecruic rapeseed cultivar. Because the word "rape" was offensive to shoppers, they called it "canola oil" and when the US approved use of the canola oil name in the late 1980s, farmers in the US started growing it in large quantity. Canola oil is lower in saturated fat, and higher in mono-unsaturates and is a better source of omega-3 fats than any other popular oils. Canola is very thin (unlike corn oil) and flavorless (unlike olive oil) so it largely succeeds by displacing soy oil, just as soy oil largely succeeded by displacing cottonseed oil.


Industrial uses

  • Vegetable oils are increasingly being used in the electrical industry as insulators as vegetable oils are non-toxic to the environment, biodegradable if spilled and have high flash and fire points. However, vegetable oils have issues with chemical stability (there has to be a tradeoff with biodegradability), so they are generally used in systems where they are not exposed to oxygen and are more expensive than crude oil distillate. Three examples are Midel 7131 by M & I materials, FR3 by Cooper Power and Biotemp by ABB. Midel 7131 is a synthetic oil, manufactured by an alcohol + acid reaction.
  • Common Vegetable Oil has also been used experimentally as a cooling agent in PCs.