Background of cooking oil
Cooking oil consists of edible vegetable oils derived from olives, peanuts, and safflowers, to name just a few of the many plants that are used. Liquid at room temperature, cooking oils are sometimes added during the preparation of processed foods. They are also used to fry foods and to make salad dressing.
People in many regions began to process vegetable oils thousands of years ago, utilizing whatever food stuffs they had on hand to obtain oils for a variety of cooking purposes. Early peoples learned to use the sun, a fire, or an oven to heat oily plant products until the plants exuded oil that could then be collected. The Chinese and Japanese produced soy oil as early as 2000 B.C. , while southern Europeans had begun to produce olive oil by 3000 B.C. In Mexico and North America, peanuts and sunflower seeds were roasted and beaten into a paste before being boiled in water; the oil that rose to the surface was then skimmed off. Africans also grated and beat palm kernels and coconut meat and then boiled the resulting pulp, skimming the hot oil off the water. Some oils have become available only recently, as extraction technology has improved. Corn oil first became available in the 1960s. Cotton oil, watermelon seed oil, grapeseed oil, and others are now being considered as ways to make use of seeds that were, until recently, considered waste.
The first efforts to increase output were undertaken independently in China, Egypt, Greece, and Rome, among other places. Using a spherical or conical stone mortar and pestle, vertical or horizontal millstones, or simply their feet, people began to crush vegetable matter to increase its available surface area. The ground material would subsequently be placed in sieves such as shallow, flat wicker baskets that were stacked, sometimes as many as 50 high. The matter was then pressed using lever or wedge presses. The Greeks and Romans improved this process by introducing edge runners to grind and a winch or screw to operate a lever press. Their method was used throughout the Middle Ages.
Refinements of this approach included a stamper press that was invented in Holland in the 1600s and used until the 1800s to extract oil, a roll mill invented by English engineer John Smeaton in 1750 to crush vegetable matter more efficiently, and the hydraulic press, invented by Joseph Bramah in England. The first improved screw press was invented by V. D. Anderson in the United States in 1876. His Expeller (a trade name) continuously operated a cage press. When vegetable matter was placed in Anderson's closed press, the resultant oil drained out of slots in the side. A screw increased the pressure through the cage toward a restricted opening.
Enhancements in grinding and pressing plant matter were followed by improvements in extracting the oil. In 1856, Deiss of England obtained the first patent for extraction of oil using solvents, following experiments by Jesse Fisher in 1843. At first, solvents such as benzene were pumped through the material and drained through false perforated bottoms. Later, Bollman and Hildebrandt of Germany independently developed continuous systems that sprayed the material with solvent. Both methods were eventually improved, and today solvent extraction is standard in the vegetable oil industry.
Cooking oil manufacture involves cleaning the seeds, grinding them, pressing, and extracting the oil from them. In extracting, a volatile hydrocarbon such as hexane is used as a solvent. After extracting, the oil is refined, mixed with an alkaline substance, and washed in a centrifuge. Further washing and refining follows, and then the oil is filtered and/or distilled. It is then ready for packaging.
Cooking oil manufacture involves cleaning the seeds, grinding them, pressing, and extrading the oil from them. In extracting, a volatile hydrocarbon such as hexane is used as a solvent.
After extracting, the oil is refined, mixed with an alkaline substance, and washed in a centrifuge. Further washing and refining follows, and then the oil is filtered and/or distilled. It is then ready for packaging.
Over time extracting vegetable oils has become more and more efficient. The very earliest methods of pressing the vegetable matter probably obtained, at best, 10 percent of the oil available. On the other hand, more modern methods involving solvent extraction can extract all but. 5 to 2 percent of the oil.