—The very finest quality of olive oil is that derived from the hand-picked olive. Just as in the preparation of fruits for the market the very best qualities are carefully picked one by one from the tree, so in the preparation of the highest grade of oil the olives are picked one by one, only those of uniform maturity and character being selected. This specially selected fruit is pressed cold, and the first running from this pressure collected separately is designated in English by the term “virgin oil.” Virgin olive oil, therefore, ranks the highest in quality. Unfortunately the use of the term for commercial purposes has not been restricted to the quality of oil to which it actually belongs, and at the present time the expression “pure virgin olive oil” which is placed upon the bottles or containers is no guarantee that this quality of oil is found therein. In fact, this expression upon the label has been found in many instances of olive oil highly adulterated and belonging to the cheapest grade. It would be impossible here to enumerate all the different names by which olive oil is found upon the market. The consumer has to depend for protection upon his knowledge of the character of the dealer and hereafter, to a greater extent than ever before, he may be protected by the application of the pure food laws of the various countries.
After the first pressing from which the best oil is secured the resulting pomace is removed from the press, heated or mixed with hot water, and again subjected to a much higher pressure from which a second quantity of oil is secured, still suitable for edible purposes but of a lower quality than that first produced. While the oils which are obtained in this way are used largely for technical purposes such as lubricating, soap making, etc., they are not infrequently employed as edible oils.
In the largest establishments for the preparation of olive oil the kernels are separated from the pulp, but in the smaller works the pulp and kernel are pressed together. Finally the residue from the second pressure may be dried and extracted with bisulfid of carbon or petroleum ether, by which means practically all the residual oil which the cake contains may be secured. Oils extracted in this manner are wholly unfit for edible purposes and are used or should be used solely for technical purposes, among which soap making is perhaps the most important.
Olive-kernel Oil.
—An oil is extracted from the kernel of the olive which in some respects of physical and chemical properties resembles olive oil itself. It is usually not considered suitable for edible purposes. Its taste resembles more that of almond oil than that of olive oil. Some of this oil is doubtless mixed with olive oil when the pulp and kernel of the olive are pressed together, but the quantity thus secured is not very great and does not introduce into the substance anything which gives a specific reaction. It is by no means as high a grade of oil as that expressed from the flesh of the olive alone.
Peanut Oil.
—Peanut oil is the refined expressed oil of the peanut, prepared in the manner above described, and is highly valued as a table or salad oil and, unfortunately, is used very often as an adulterant of olive oil, the mixture being sold under the name of the more valuable of its constituents.
Peanut oil contains arachidic acid, which in combination with glycerine forms one of the constituents which serves to distinguish it particularly from other edible oils. There is no other edible oil which contains arachidic acid in sufficient quantities to lead to any mistake concerning its relationship to peanut oil.
Renard’s Test for Peanut Oil as Modified by Tolman.
—Place 20 grams of oil in an Erlenmeyer flask. Saponify with alcoholic potash, neutralize exactly with dilute acetic acid, using phenolphthalein as indicator, and wash into a 500 c.c. flask containing a boiling mixture of 100 c.c. of water and 120 c.c. of a 20 percent lead acetate solution. Boil for a minute, and then cool the precipitated soap by immersing the flask in water, occasionally giving it a whirling motion to cause the soap to stick to the sides of the flask. After the flask has cooled, the water and excess of lead can be poured off and the soap washed with cold water and with 90 percent (by volume) alcohol. Now add 200 c.c. of ether, cork the flask, and allow to stand for some time until the soap is disintegrated, then heat on the water bath, using a reflux condenser, and boil for about five minutes. In the oils most of the soap will be dissolved, while in lards, which contain so much stearin, part will be left undissolved. Cool the ether solution of soap down to from 15° to 17° C., and let stand until all the insoluble soaps have crystallized out—about twelve hours are required.