History—In ancient Egypt the olive was known by the term bāk; it can be traced as far as the 17th century before our era.[1540]
According to the elaborate investigations of Ritter[1541] and of A. De Candolle,[1542] the olive tree is a native of Palestine, and perhaps of Asia Minor and Greece. Its original area also extends over north-eastern Africa; Schweinfurth[1543] regards it as undoubtedly wild on the mountains of Elbe and Soturba in lat. 22 N. on the western shores of the Red Sea, a locality which he visited in 1868. The olive tree has also been met with as far eastward as the country of the Gallas, where it is much appreciated as affording excellent timber.[1544] It is also stated by Theophrastus, that in his time the tree was plentiful in the Cyrenaica, the modern Barca, in northern Africa.
The olive would appear to have been introduced at a very remote period into north-western Africa and Spain. Willkomm (1876) is of the opinion that it was originally a native of the whole Mediterranean region.
At the present day it is largely cultivated in Algeria, Spain, Portugal, Southern France, Italy, the Greek Peninsula and Asia Minor. In the Crimea the tree grows well, but does not afford good fruit. It was carried to Lima in Peru about 1560 and still flourishes there, and in great plenty in the coast valleys further south as far as Santiago in Chili.[1545]
Olive oil is mentioned in the Bible so frequently that it must have been an important object with the ancient Hebrews. It held an equally prominent place among the Greeks and Romans,[1546] whose writers on agriculture and natural history treat of it in the most circumstantial manner. Olive fruits preserved in brine were used by the Romans as an article of food,[1547] and were an object of commerce with Northern Europe as early as the 8th century.[1548]
Production—In common with many important cultivated plants, the olive occurs under several varieties differing more or less from the wild form, the finer of which are propagated by grafting. It is also increased by the suckers which old trees throw up from their naked roots, and which are easily made to develope into separate plants.[1549] The fruit, an oval drupe, half an inch to an inch or more in length, and of a deep purple, is remarkable for the large amount of fat oil contained in its pulpy portion (sarcocarp). The latter is most rich in oil when ripe, containing then nearly 70 per cent., besides 25 per cent. of water. The unripe fruit, as well as other parts of the plant, abounds in mannite, which disappears in proportion as the oil increases. The ripe olive contains no mannite, it having probably been transformed into fatty oil.[1550]
The process for extracting olive oil varies slightly in different countries, but consists essentially in subjecting the crushed pulp of the ripe fruit to moderate pressure. The olives, which are gathered from the trees, or collected from the ground, in November, or during the whole winter and early spring, are crushed under a millstone to a pulpy mass. This is then put into coarse bags, which, piled upon one another, are subjected to moderate pressure in a screw press. The oil thus obtained is conducted into tubs or cisterns containing water, from the surface of which it is skimmed with ladles. This is called Virgin Oil. After it has ceased to flow, the contents of the bags are shovelled out, mixed with boiling water, and submitted to stronger pressure than before, by which a second quality of oil is got. If the fruit is left for a considerable time in heaps it undergoes decomposition, yielding by pressure a very inferior quality of oil called in French Huile fermentée. The worst oil of all, obtained from the residues, has the name of Huile tournante or Huile d’enfer.
It is said that in some districts the millstones are so mounted as to crush the pulp without breaking the olive-stones, and that thus the oil of the pulp is obtained unmixed with that of the kernels.[1551] We have made many inquiries in Italy and France as to this method of oil-making, but cannot find that it is anywhere followed.
The fixed oil of the kernels of ripe olives has been extracted and examined by one of us (F.). Though the kernels have a bitterish taste, the oil they yield is quite bland; by exposure to the vapour of hyponitric acid, it concretes like that of the pulp. If the whole of it were extracted in making olive oil, it would only be about as 1 part of oil of the kernel, to 40 parts of oil of the pulp.
Description—Olive Oil is a pale yellow or greenish yellow, somewhat viscid liquid, of a faint agreeable smell and of a bland oleaginous taste, leaving in the throat a slight sense of acridity.[1552] Its specific gravity on an average is 0·916 at 17° C. In cold weather, olive oil loses its transparency by the separation of a crystalline fatty body. The deposition takes place at a few degrees above the freezing point of water, and in some oils even at 10° C. (50° F.) If the oil is allowed to congeal perfectly, and is then submitted to strong pressure, about one-third of its weight of solid fat may be separated. After repeated crystallizations, this fat melts at 20 to 28° C. The fluid part or Olein, continues fluid at -4° to -10° C. Olive oil belongs to the class of the less alterable, non-drying oils.