OLIVE OIL. An oil expressed from the fleshy part (peri carp) of the fruit of the olive tree, which is chiefly cultivated in the countries bordering on the Mediterranean, and recently with some success in California, South Africa and Australia. The ripe fruit contains from 20 to 6o% of oil, depending on climatic con ditions and on the care exercised in cultivation. Californian and North African olives usually contain less oil than those grown in France or Italy.
The fruit intended for oil production should be gathered just before it is fully ripe. The finest quality oil, termed "virgin oil," is prepared from hand-picked fruits by gentle pressing ; in some cases the pulp is stripped from the pits before treatment; this oil is not exported. The apparatus used in expressing the oil varies from the most primitive form of press, consisting of two boards weighted with stones, to the most modern types of hydraulic presses (see Coco-Nu r OIL; also In order to obtain the best quality edible oil it is essential that the oil be removed from contact with the putrescible marc (pulp) as soon as possible, par ticularly if the fruit was bruised; otherwise rancidity sets in with consequent formation of free fatty acids. In practice the pulp is pressed twice, yielding first and second grade edible oils; it is then mixed with hot water and subjected to further pressure, yielding technical oils. The press residues are ground up with hot water and run into settling tanks; the oil which rises to the top, termed "huile de ressence," is skimmed off. A still lower
quality oil, "sulphur olive oil," is obtained by extracting the residue with a volatile solvent, usually carbon disulphide.
The product known as "Tournant oil" is obtained by allowing the expressed marc to ferment, whereby the cells are ruptured and more oil is liberated. As this oil contains a large amount of free fatty acids it forms a stable emulsion with sodium carbonate which is used as a Turkey-red oil.
Olive oil for edible purposes, which should be practically devoid of free fatty acids, varies in colour from water-white to golden yellow, and possesses a smooth bland taste, varying with the district in which the olive is grown and also the degree of ripeness of the fruit. In general the oils from North Africa and Greece have a harsher taste than those from Provence and Tuscany. Olive oils intended for use in cold climates should remain limpid at le C, and are prepared by cooling the oil to below that temperature and settling-out the deposited "stearine." Olive oil is extensively adulterated, chiefly with tea seed, arachis and sesame oils. The bulk of the oil produced is used for comestible purposes (preserving sardines, etc.) ; it is also used for oiling wool and for the manufacture of high-class toilet and textile soaps (q.v.), known as Castile soap. The pro duction of oil in the principal olive growing countries for 1937 is given below:— • From International Institute of Agriculture Review.
See also OiLs. (E. L.; G. H. W.; X.)