3. (Second quality.) By allowing the bruised fruit to ferment before pressing it. Yellow; darker than the preceding; but mild and sweet tasted. Much used for the table.
4. (‘Gorgon.’) By fermenting and boiling the pressed cake or marc in water, and skimming off the oil. Inferior.
5. (Oil of the infernal regions; Oleum omphacinum) is a very inferior quality of oil, which is skimmed off the surface of the water in the reservoirs into which the waste water which has been used in the above operations is received, and allowed to settle. The last two are chiefly used for lamps, and in soap-making, &c.
Of the principal varieties of olive oil known in commerce, and distinguished by the place of their production, ‘Provence oil’ is the most esteemed; ‘Florence oil’ and ‘Lucca oil’ are also of very fine quality; ‘Genoa oil’ comes next, and then ‘Gallipoli oil,’ which forms the mass of what is used in England; ‘Sicily oil,’ which has a slightly resinous flavour, is very inferior; and ‘Spanish oil’ is the worst imported.
Prop., &c. Olive oil is a nearly inodorous, pale greenish-yellow, unctuous fluid, with a purely oleaginous taste, peculiarly grateful to the palate of those who relish oil. It does not suffer active decomposition at a heat not exceeding 600° Fahr.; and when cooled to 36°it congeals into a granular solid mass. It is very slightly soluble in alcohol, but its solubility is increased by admixture with castor oil. It is soluble in 11⁄2 part of ether. When pure it has little tendency to become rancid. Sp. gr. ·9170 to ·9173; ·9192, at 531⁄2° (Saussure); ·9176, at 59° (Heidenreich); and ·9109, at 77° Fahr. (Saussure). Prod. 32%, of which 21% is
furnished by the pericarp, and the remainder, which is inferior, by the seed and woody matter of the fruit.
Pur. Olive oil, with the exception of that of almonds, being the most costly of the ordinary fixed oils of commerce, is, consequently, the one most subject to adulteration. Nut, poppy, rape, and lard oil, are those most commonly used for this purpose. Refined tallow olein, including that obtained from the ‘knackers’ yards’ of Paris, is said to have been used in the same way. The addition of any other oil to olive oil renders it far less agreeable to the palate, and, by increasing its tendency to rancidity, much more likely to offend and derange the stomach and bowels of those who consume it. Parties who indulge themselves in the use of this luxury would, therefore, do well to ascertain that what they purchase is pure. When pure, and also fresh, olive oil is most wholesome as an article of food or us a condiment.
The detection of the sophistication of salad oil is a matter of no great difficulty. The palate of the connoisseur will readily perceive the slightest variation in the quality of his favourite condiment. Other methods, however, of a more accurate and certain description, and of more general application, are adopted. Amongst these, in addition to those mentioned above, are the following:—
a. When pure olive oil is shaken in a phial, only half filled, the ‘bead’ or bubbles rapidly disappear; but if the sample has been mixed with poppy or other oil, the bubbles continue longer before they burst.
b. Olive oil congeals at 36° Fahr., and is completely solidified when a small bottle containing it is surrounded by ice, or a freezing mixture; but when mixed with poppy oil, it remains partly liquid, even when the latter forms only 1-4th of the mass; if more than 1-3rd of poppy oil is present, it does not solidify at all, unless cooled much below the freezing point of water.