Olive (Olea europaea)
OLEACEAE, Olive Family
The olive (Olea europaea) is a tree with simple, opposite decussate evergreen leaves. The plant is native to the eastern area of the Mediterranean, where it grows in chaparral (maquis), but this crop is widely planted in all areas that have mediterranean-type climate. Most olive production is centered in southern Europe, Iberia, semiarid northern Africa, and the Middle East, where olive groves are maintained with irrigation, but some olive production occurs in California (33,000 acres), where the crop was introduced by Catholic priests at Mission San Diego in 1769. New plants are generally started from seed, and olives generally are not grafted. In addition to the use of fruits as food and olive oil, the wood has numerous special purposes, and the plants are widely used in landscaping. This species is killed by prolonged below-freezing temperatures.
The fruit is a drupe that develops from small, white flowers, which are wind- or insect-pollinated. In some desert communities, olive pollen causes serious hayfever pollution.
Olives are harvested in the late autumn. Traditionally, a cloth was spread beneath the tree and the fruits were then dislodged by rakes or shaking. In a good grove, one can harvest over 7 tons of olives per acre. Worldwide, nearly 900,000 tons of table olives are produced, but 90% of all oils are used to press olive oil (1.66 million tons). Olives for oil are harvested when they are fully ripe, black or dark brown. Table olives, either green or black, generally are harvested before they are ripe.
Raw olives cannot be eaten because they contain the bitter glucoside oleuropein, which must be neutralized. Unripened olives are processed in several ways. The simplest method, still used in home curing, is to salt them or soak (submerge) in a strong salt solution (one cup of salt per quart of water), and twice a day throw out the bitter fluid. Commercial production of green Spanish olives involves soaking in lye (sodium hydroxide), then 6 to 12 months in a weak salt solution (brine) to promote lactic fermentation. Soaking in brine also tenderizes the parenchymatous mesocarp. Black olives, such as the wonderful pitted Kalamata olives in Greek salads, are produced from lye curing and oxygenation. Afterwards, fruits are stored in dilute brine, olive oil, or vinegar, and sterilized before packing. The "stone," i.e., the endocarp, may be removed, and the olives can also be stuffed with pimento (Capsicum).
Olives are extremely rich in oils--14 to 40% by weight. Approximately 75% is oleic acid (named after the genus!) with some palmitic and linoleic acid. Olive oil, though high in calories, is claimed to raise high-density lipids (HDLs, the good ones), in a way similar to canola oil. Olive oil does not form a film after exposure to air, and therefore is a nondrying oil. The fruit is most commonly crushed, as chilled, between two vertical stone wheels, each weighing about two and a half tons. The olive paste then is spread on mats, stacked, and placed in an hydraulic press with 9000 pounds of pressure per square inch. From that, the extracted liquid enters a large centrifuge, which separates the triglycerides from the water fraction. This first pressing is termed "extra virgin olive oil" and is the fruitiest, nonacid, and most expensive, used on the finest salads. A product termed "virgin olive oil" may also come from the first pressing, but has an acid concentration of 1-3%, especially from fruits that are not the choice ones, or may come from a second or third pressing. The commercial grade olive oil usually involves extracting triglycerides with heat, pressure, and solvents, from two to four pressings. Nowadays, light olive oil has appeared; this is not lower in calories or different triglycerides, but has undergone fine filtration, which permits this oil to be used for high-heat frying.