_Olive Oil_; _Salad Oil_; F. _Huile d’Olives_; G. _Olivenöl_; _Baumöl_;
_Provencer Oel_.
=Botanical Origin=—_Olea europæa_ L., an evergreen tree,[1537]
seldom exceeding 40 feet in height, yet attaining extreme old age,
abundantly cultivated in the countries bordering the Mediterranean,
up to an elevation of about 2000 feet above the sea-level.[1538]
_Olea ferruginea_ Royle (_O. cuspidata_ Wallich), a tree abundant in
Afghanistan, Beluchistan and Western Sind, has been supposed to be
a wild form of _O. europæa_, but is regarded by Brandis[1539] as a
distinct species. It is not known to have been ever cultivated, yet its
fruit, which is of a small size and but sparingly produced, is capable
of affording a good oil.
_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.
[1534] _Comptes Rendus_, xlvi. (1858) 1276; Gmelin, _Chemistry_, xv.
299.
[1535] Belon, _Singularitez_ (1554) l. 2. cap. 91; Guibourt, _Comptes
Rendus_ (1858) 1213; Hanbury, _Journ. Linn. Soc._, Zoology, iii. (1859)
178; also _Science Papers_, 158.
[1536] Dobson, _Proceedings of Royal Society of Van Diemen’s Land_, i.
(1851) 234; _Pharm. Journ._ iv. (1863) 108; Flückiger, _Wittstein’s
Vierteljahresschrift_, xvii. (1868) 161; _Archiv der Pharmacie_, 196
(1871) 7; abstracted in the _Yearbook of Pharmacy_, 1871. 188.
[1537] Readers desiring full information about the olive tree, its oil,
its history, etc., should refer to the extremely exhaustive work of
Coutance, _l’Olivier_, Paris, 1877, 456 pages, 120 figures.
[1538] Grisebach states the elevation above the sea of
olive-cultivation thus:—Portugal (Algarve) 1400 feet; Sierra Nevada
3000; do., southern slope 4200; Nice 2400; Etna 2200; Macedonia 1200;
Cilicia 2000.—_Die Vegetation der Erde nach ihrer klimatologischen
Anordnung_, i. (1872) 262. 283. 342.
[1539] _Forest Flora of North-western and Central India_, 1874, 307.
[1540] Brugsch-Bey, _Reise nach der grossen Oase Kargeh_, Leipzig,
1878. 80. etc.—See also _Journ. of Botany_, 1879. 52.
[1541] _Erdkunde von Asien_, vii. (part 2. 1844) 516-537.
[1542] _Géographique Botanique_ (1855) 912.
[1543] _Bot. Zeitung_, 1868. 860.
[1544] Arnoux, _Revue des Deux Mondes_, Janvier 1879. 381.
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]
[1545] Perez-Rosales, _Essai sur le Chili_, Hambourg, 1857. 133.
[1546] Hehn, _Kulturpflanzen und Hausthiere in ihrem Uebergange
aus Asien nach Griechenland und Italien_, Berlin, 1877. 88-142,—an
interesting account of the importance of the olive in ancient times.
[1547] Specimens may be seen among the antiquities found at Pompei.
[1548] Diploma of Chilperic, A.D. 716.—Pardessus, _Diplomata_,
_Chartæ_, etc., Paris, ii. (1849) 309.
[1549] Winter, in _Pharm. Journ._ Sept. 7, 1872.
[1550] De Luca in _Journ. de Pharm._ xlv. (1864) 65.—Some further
researches by Harz on the formation of olive oil may be found in the
_Jahresbericht_ of Wiggers and Husemann (1870) 392.
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.
The foregoing description does not apply to the inferior sorts of oil,
which congeal more easily, are more or less deep-coloured, have a
disagreeable odour and taste, and quickly turn rancid. These inferior
oils have their special applications in the arts.
=Chemical Composition-=-The chief constituent of olive oil is _Olein_
or more correctly _Triolein_, C₃H₅(O·C₁₈H₃₃O)₃, identical so far as at
present ascertained with the fluid part of all oils of the non-drying
class. The proportion of olein in olive oil, as well as in other oils,
is liable to variation, the result partly of natural circumstances and
partly of the processes of manufacture. The best oils are rich in olein.
[1551] _The Grocer_, April 25, 1868, supplement; Pereira, _Elem. of
Mat. Med._ ii. (1850) 1505.
[1552] This according to our experience is the case even with oil as
it runs from the pulp and therefore in the freshest condition; but the
acrid after-taste is more perceptible in oil which has been long kept.
As to the solid part of olive oil, Chevreul believed it to be
constituted of _Margarin_, which he first examined in 1820. But
Heintz (1852 and later) showed margarin to be a mixture of palmitin
with other compounds of glycerin and fatty acids. Collett in 1854
isolated _Palmitic Acid_, C₁₆H₃₂O₂, from olive oil; and Heintz and Krug
(1857) further proved that _Tripalmitin_ is the chief of the solid
constituents of olive oil. They also met with an acid melting at 71°·4
C., which they regarded as _Arachic Acid_ (p. 187). As to stearic acid,
Heintz and Krug did not fully succeed in evidencing its presence in
olive oil.
Lastly, Benecke discovered in olive oil a small quantity of
_Cholesterin_, C₂₆H₄₄O. It may be removed by means of glacial acetic
acid or alcohol, which dissolve but very little of the oil.
=Commerce=—Various sorts of olive oil are distinguished in the English
market, as Florence, Gallipoli, Gioja, Spanish (Malaga and Seville),
Sicily, Myteline, Corfu and Mogador.
Olive oil was imported into the United Kingdom in the year 1872 to
the value of £1,193,064. Nearly half the quantity was shipped from
Italy, one-fifth from Spain, and the remainder from other Mediterranean
countries.
The average annual production in Italy is estimated at about 3 millions
of hectolitres (66 million gallons), but the quantity exported does not
reach half that amount.
The statistics of the French Government indicate the annual production
of olive oil in France to be not more than 250,000 hectolitres,
equivalent in value to 30 millions of francs (£1,200,000).[1553]
=Uses=—The uses of olive oil in medicine and its immense consumption in
the warmer parts of Europe as an article of food, are too well known to
require more than a passing allusion.
=Adulteration=—Olive Oil is the subject of various fraudulent
admixtures with less costly oils, the means of detecting which has
engaged much attention. Of the various methods by which chemists have
endeavoured to ascertain the purity of olive oil, the following are the
more noteworthy:—
=a.= Drying oils (such as the oils of poppy and walnut) may be
distinguished by their not being converted into solid crystallizable
elaidin by hyponitric acid or concentrated solution of nitrate of
protoxide of mercury. Olive oil which contains any considerable
proportion of one of these oils, no longer solidifies if exposed for a
moment to one of the above-mentioned reagents. This test however is not
of sufficient delicacy for small amounts of drying oils.
=b.= Olive oil being one of the lighter oils, the specific gravity may
to some degree indicate admixture with a heavier oil. To make use of
this fact, Gobley and other chemists have invented an instrument called
an _elaiometer_, for taking the specific gravity of oils.
=c.= Observation of the Cohesion-figure.—This test, proposed by
Tomlinson in 1864,[1554] depends on the forces of cohesion, adhesion,
and diffusion. Thus, if a drop of any oil hanging from the end of a
glass rod is gently deposited upon the surface of chemically clean
water, contained in a clean glass, a contest takes place between the
forces in question the moment the drop flattens down by its gravity
upon the surface of the water. The adhesion of the liquid surface tends
to spread out the drop into a film, the cohesive force of the particles
of the drop strives to prevent that extension, and the resultant of
these forces is a figure which Mr. Tomlinson believes to be definite
for every independent liquid. The figure thus produced is named the
_cohesion-figure_.
[1553] Exposition de 1867 à Paris, _Rapports du Jury International_,
xi. 108.—In the work of Coutance, quoted p. 417, note 7, nearly 400,000
hectolitres are calculated for the year 1866.
[1554] _Pharm. Journ._ v. (1864) 387. 495, with figures.
So far as our experience goes, the processes hitherto recommended for
testing olive oil (and there are several that we have not mentioned)
are only available in cases where the adulteration is considerable, and
are quite insufficient for discovering a small admixture of other oils.
How little they are appreciated, may be inferred from the fact that the
Chamber of Commerce of Nice[1555] offered a reward of 15,000 francs
(£600) for a simple and easy process for making evident an admixture
with olive oil of 5 per cent. at least of any seed-oil.