OLIVE, one of the leading fruits of the world. It is borne by a small tree (Olea europæa) of the order Oleaceæ, and is the most important member of its genus, which includes between 30 and 40 species. This tree is a native of western Asia and probably of the Mediterranean region, and attains a height of about 25 feet, bears small lanceolate evergreen leaves and axillary racemes of fragrant yellowish-white flowers followed by oblong or ovoid fruits (drupes). From remote antiquity it has been cultivated as a food-plant, especially for the oil pressed from its fruits. Throughout the coast of the Mediterranean the olive has been grown upon a commercial basis for many centuries, individual trees being known to be more than 1,000 years old. It was introduced during the 18th century into California, which is now the leading olive-producing district o£ the United States, but part of Arizona and New Mexico are adapted to olives and are gradually coming into notice. The assumption is made that seed was introduced in 1769 from Mexico and planted at the San Diego Mission, whence cuttings were taken to other missions throughout California; and this olive, the only one known in the State until about 1880, was called the “Mission” variety. Since 1880 numerous varieties have been introduced from olive-growing countries of Europe.
The olive succeeds best in warm, dry climates. It will withstand some frost, but at blossoming time this is believed to impair if not to destroy the crop; and the same result is often attributed to high wind and very dry air at that time. A rich, well-drained soil is preferred, but the tree will succeed and produce excellent crops upon a very great variety of soils; it is usually a mistake, however, to plant it upon rocky hillsides, as too numerous failures in California prove. While not exacting as to food, the trees must have an adequate fertilizer. To return to the soil of the pomace after the oil has been expressed, together with slight dressings of commercial fertilizers and judicious cultivation, will keep the trees in lusty bearing condition. The trees are usually set about 30 feet apart either in hexagons or in squares, the former plan being preferred in California because it is more economical of land, and permits of plowing in three directions instead of only two. The land is kept cleanly cultivated throughout the season.
The olive is propagated by layers, suckers, sprouts, cuttings, tips of twigs, grafts, buds and seeds. The last three, being tedious and slow, are rarely employed. The favorite method is by means of tips. These are obtained from small dormant branches, partly defoliated, rooted in moist sand and then transplated in nursery rows. The trees should begin to bear when about eight years old and reach full productivity when about 30.
Olive Oil. — The principal uses of the olive are for oil production, for pickling, either green or ripe, and for drying. For the production of oil, the ripe fruits are carefully gathered by hand, bruised as little as possible and preferably crushed at once, otherwise they are partially dried in very thin layers through which air must circulate freely to avoid molding and fermenting, unsound fruit being prone to decay and impair the flavor and odor of the oil. An old practice was to crush the fruit by means of heavy mill-stones in pits, but the oil thus extracted from the kernels has been found to injure both the flavor and the keeping quality of the oil obtained from the pulp. Modern crushers, therefore, do not break the stones. The crushed pulp is then pressed in linen sheets, the pressure being applied very gradually. A second pressing is made after the pulp has been mixed with cold water. Other pressings are sometimes given, each one resulting in a grade of oil inferior to the preceding. The two first grades are sometimes mixed. Since the separation of the oil from the juice by gravity is hazardous on account of liability to ferment, the impurities are washed out quickly by special apparatus in which a current of cool water comes in contact with a small quantity of the juice, mixes with it, separates the larger particles of pulp and allows the oil to rise through a tall column of water which further washes the oil-globules as they rise. After being allowed to stand for a time in a cool room this oil is racked off and sold as “new oil,” or may be again allowed to stand for further clarification. Since the American market demands a clear oil, however, much of the domestic oil is filtered, a process which, especially if often repeated, impairs the flavor and makes the oil seem greasy. Throughout the process, scrupulous cleanliness is essential, because olive oil is prone to absorb any taint either in the utensils or in the air. The oil is pale yellow, inodorous, and has a specific gravity of .918 at a temperature of 15° C. It is largely used in cookery and pharmacy, for lubricating and illuminating purposes, and for making Castile and other kinds of soap, for which purpose the lower grades are most employed. In the United States it is often adulterated with cottonseed-oil. Gallipoli oil, which is used in dyeing, is made from the fermented fruit.
Olive oil also has important medical uses. In doses of from one to two ounces for adults, and one teaspoonful for infants, it acts as a laxative. It is also used in intussusception of the bowels; as an antidote in cases of acrid poisoning; as a local neutral protective from the atmosphere; in place of suet, lard, etc., as an inunction to increase the fat of the body, or to reduce the heat of the skin, and by workmen in lead factories as a laxative, and to prevent the absorption of lead. Combined with camphor, morphine, etc., it is applied to wounds, burns and bruises, and forms the basis of many liniments. It is used to allay the pain of insect bites, and (warmed) in the ear, to destroy insects. It is also employed as an application to swollen breasts, as a lubricant of surgical instruments, sounds, pessaries, etc., and as an injection in cases of constipation; but for this last purpose it is inferior to castor oil. In large doses, it is believed by some physicians to hasten the discharge of gall-stones, sometimes apparently softening them.
Pickled Olives. — For pickling the fruits are gathered by hand before they are likely to become soft during the process, a degree of maturity not readily described except by saying that the time is just before the fruits would change from green to the mature fruit tint, which varies with the variety from yellow to almost black. They are first placed either in pure water, which must be changed each day, or in a weak solution of lye. This is to remove the bitterness and acridity and to soften the skin. After the latter process, which may occupy from one to three months, the lye is removed by soaking in pure water. Then the olives are subjected to a series of immersions in salt solutions of gradually increasing strength, the maximum being dense enough to float an egg. They will now keep for years if properly stored. Pickled green olives are much less a food than a table delicacy or relish; but pickled ripe olives, which are prepared by much the same process and are gaining in favor, are considered primarily as a food. However, there is little difference in their food value. Dried olives are popular in some Mediterranean countries, but are little known in the American market.
The average composition of pickled green olives is: water, 58; fat, 27.6; carbohydrates, 4.3; protein, ash, etc., 7.8; that of pickled ripe olives: water, 65.1; fat, 25.5; carbohydrates, 3.8; protein, ash, etc., 5.6.
Besides the species mentioned above, several other related species are valued more or less. Olea chrysophylla, a tropical African species, has been introduced into southern California, where it is planted for ornament, the under surfaces of the leaves being bright golden yellow. Olea, or Osmanthus, fragrans, is the fragrant olive of China and Japan, where its flowers are used for perfuming tea. It is also cultivated in greenhouses for its inconspicuous but exceedingly fragrant flowers.
In ancient Greece the olive was sacred to Pallas Athene and was a symbol of chastity and peace. Like the laurel it was used for making wreaths for crowning the victors in athletic sports. Olive wood is very hard and beautifully grained, and is valuable for cabinet work.
Olives vary in size from 100 to more than 400 to the pound. The exports of the United States are about 6,000,000 gallons of oil and 5,000,000 gallons of green olives. The United States production of olive oil in 1912 amounted to 350,000 gallons.
Consult Bailey, ‘Cyclopedia of American Horticulture’ (1900-02); Goldmann, F., ‘Der Oelban in Palästina’ (Freiburg 1897); Hayne, ‘California Experiment Station Bulletin No. 129’ (1900); Neville-Rolfe, E., ‘Report on the Cultivation of the Olive in Italy’ (London 1897); Pierce, N. B., ‘Olive Culture in the United States’ {United States Department of Agriculture, Yearbook 1896).