Edible Vegetable Oils.
While there is very little chemical difference between the fats of animals and the oils of plants, the difference is sufficiently distinguished to secure a proper degree of identification and classification. Both classes of bodies are composed of the fatty acids combined with glycerine. The three fatty acids which are most important from the edible point of view and also from the chemical are oleic, stearic, and palmitic. When these acids are united with glycerine as the basic element, they form three classes of oils or fats to which the names olein, stearin, and palmitin are respectively given. A distinction may also be made between a fat and an oil by observing its physical consistence at ordinary room temperature of approximately from 70 to 80 degrees F. It is usual to speak of the bodies which are liquid at such temperature as oils, while those that are solid under like conditions are known as fats. A compound of this description does not pass suddenly from one state to another. In the case of a fat, for instance, which is solid at ordinary temperature, it passes by gradual stages from that condition to a slowly softening mass and then to a complete liquid as the temperature is raised. On the other hand, an oil passes gradually through the same stages to the condition of a solid body as the temperature is lowered. Of the different constituents the olein has the lowest melting point, pure olein being still liquid at quite a low temperature, approaching even the freezing point of water. Stearin and palmitin on the contrary, if in a pure state, are solid at a temperature even above that of the room and above that of blood heat. In the mixture of these bodies it is evident that a complicated structure must be present which is composed of different bodies of varying melting points and passing through all different degrees of temperature from a solid to a liquid state or vice versâ. It is evident that an oil has a larger proportion of olein in its composition and a fat a larger proportion of stearin and palmitin.
Animal fats are composed chiefly of olein and stearin, while strictly vegetable oils are principally olein, and palm oil is composed chiefly of stearin and palmitin.
In butter fat there is introduced an important additional compound of a fatty acid with glycerine, namely butyrin, which is made up of a union of glycerine with butyric acid. Butter also contains other components or glycerids, but in small quantities. Oleic, stearic, and palmitic acids are insoluble in water and not volatile at the boiling point of water. Butyric acid is soluble in water and is volatile at the boiling point of water. The first kinds of acid are therefore called “fixed” and the second “volatile.”
The edible vegetable oils like the animal fats are highly nutritious in the sense that they afford to a greater degree than any other kind of food product the elements necessary to the production of heat and energy. The average number of calories to one gram of edible oil is in round numbers 9,300. When this number is compared with the average number of calories in one gram of sugar or starch, namely 4,000, it is seen that fats and oils are two and one-fourth times as valuable as sugar in the production of heat and energy. Since the greater part of the food consumed by an animal is utilized in the production of heat and energy, it is seen that the fats and oils must be classed as the most concentrated and in that sense the most valuable human foods.
The use of edible vegetable oils is also advisable for hygienic purposes. They are readily assimilated and digested, and they produce a physical effect upon the process of digestion which is a matter of importance. The free use of edible vegetable oils is to be recommended in cases of constipation or where there are mechanical difficulties in the digestive process. In these cases it is consumed in larger quantities than would ordinarily be the case.
Use of Edible Oils.
—The edible oils are used most extensively on the table as the base of salad-dressing. Many succulent vegetables, as has already been stated, are eaten very commonly with condimental substances such as vinegar, salt, spices, etc., and as a vehicle for these condimental substances there is nothing superior or even equal to the edible vegetable oils. Vinegar, itself, owes its active principle, namely, its acid, to a member of the fatty acid series, so that the mixture of vinegar with oil is not a bringing together of two wholly different substances but of two substances belonging to the same general family. Vinegar itself has no value as a food, but is useful solely for condimental purposes. On the other hand the edible oil is not only condimental, increasing the pleasant taste of the compound, but also has a high food value. Edible oils may also be used in the place of lard and other animal fats in the preparation of bread and pastry, serving the purpose of shortening. Edible oils are also highly useful as a vehicle for frying foods, such as oysters, croquettes, doughnuts, etc.
The heating of an oil or fat to a high temperature produces a certain degree of decomposition with a development of an aromatic and sometimes unpleasant product known as acrolein. It is not believed that this change is as detrimental to digestion as is commonly supposed. Products which are fried in oil, or boiled in oil, which is probably a better term, as described above, are not to be considered wholly indigestible, though it cannot be denied that they are not the best things for delicate stomachs or those which are in any way weakened by disease. In the case of a healthy individual, however, a moderate quantity of such products may be eaten without any great danger of producing a derangement of digestion. If these bodies are found to be indigestible, it is probably not due to the fact that they contain large quantities of oil but rather to the decomposition effected by the high temperature and the hardening of the periphery of the bodies to such an extent as to make them difficultly amenable to the activities of the digestive ferments.
Acorn Oil.
—The oil of the acorn is sometimes used for edible purposes. It is extracted by pressure, and the nature of the product depends upon the variety of the acorn. Acorn oil has at 15 degrees a specific gravity of .916 and an iodin number of 100. It is not of any commercial importance as an edible oil.
Almond Oil.
—Almond oil is not so commonly used for edible purposes as it is for pharmaceutical preparations. By reason of its flavoring properties, however, it may sometimes be used for food purposes, and a brief description, therefore, is advisable.
Almond oil is obtained from the seed of the bitter almond, a variety of Amygdalus communis L. It may also be extracted from the seeds of the sweet almond, but these contain less oil than the bitter almond seed and the oil is not so useful for flavoring purposes. The bitter almond whose seeds are used for the extraction of oil are grown chiefly in Morocco, the Canary Islands, Portugal, Spain, France, Italy, Sicily, Syria, and Persia. The almond kernel contains about 40 percent of oil. Almond oil is said by most observers to be free from stearin, and it is therefore an oil which is composed almost exclusively of olein. The specific gravity of almond oil at 15 degrees C. is almost exactly that of rapeseed oil, being only a trifle higher. The average number expressing the specific gravity at that temperature is .918. Its iodin value is slightly lower than that of rapeseed oil, being about 97.
Adulterations.
—Almond oil is often adulterated with other cheaper oils. Among these those which are principally used are cottonseed oil, walnut oil, poppyseed oil, sesamé, peanut, apricot-kernel and peach-kernel oil, and lard oil. Those most frequently used are the apricot and peach, since these oils contain the characteristic principle which gives the bitter taste to the kernels of this class in fruits. Often almond oils are offered to the trade which are composed exclusively of peach-kernel or apricot-kernel oil. Whenever the iodin number of an almond oil runs very high it is an indication that it is composed largely of peach or apricot oil. The detection of small quantities of these oils when added to almond oil is a very difficult matter and can only be accomplished by the expert chemist.
Cottonseed Oil.
—One of the most important edible oils in the world, and especially from the point of view of production in the United States, is that derived from the seed of the cotton plant (Gossypium herbaceum).
The cotton plant grows over a wide area in the United States, including all of the southern states and extending into southern Virginia, southern Kentucky, southern Missouri, and Oklahoma. In former years the cotton plant was cultivated solely for its fiber. It is only in the last quarter of a century that the high value of its seed for many purposes has been realized. The seed of the cotton plant is preëminently rich in oil and protein. It contains traces of certain poisonous alkaloids, betain and cholin, the presence of which renders its indiscriminate use for cattle food in some cases dangerous. In the preparation of oil, however, no trace of these poisonous substances is found, since they exist solely in the non-fatty tissues of the seed. The production and refining of the oil has now grown to be a great industry and has already added much to the wealth of the cotton growers and the comfort and nutrition of the people in general.
Magnitude of the Cottonseed Oil Industry.
—The average cotton crop of the United States is about 12,000,000 bales of about 500 pounds each. For every bale of cotton there is produced 1,000 pounds of seed. This would make the average cottonseed crop of the country about 6,000,000 tons. It is estimated that not over two-thirds of this is used in the mills; this would make about 4,000,000 tons. The average yield of 40 gallons to a ton shows the production of crude oil to be 3,200,000 barrels of 50 gallons each. This oil in refining loses on the average about 8 percent, which would leave 2,944,000 barrels of refined oil for edible and other purposes. Not less than two-thirds of this oil is used for edible purposes. A conservative estimate would place the quantity used for food between two millions and two millions and a half barrels per annum. The quantity varies with the prices of other fats.
Cotton seed is brought to the mills from the gins either by rail in box cars or in wagons. On arrival at the mills, it is stored in large sheds, known as seed houses. A single seed house will often contain as much as 5,000 to 10,000 tons. The seed is carried into the mill by means of conveyers. It first goes through coarse screens which remove the greater part of the trash and sand, after which it is passed over magnetized iron plates which remove nails and pieces of iron which may have accidentally gotten into the seed. After the seed is thoroughly cleaned it passes through gins known as linters, which remove from 40 to 50 pounds of short staple cotton known in the trade as “linters.” This cotton is used for preparing cotton batts, mattresses, etc. Conveyers carry the seed from the linters to the hullers, which are rapidly revolving drums covered with cutting knives which chop up the seed. From the hullers the cut-up seed pass over a series of screens where the meats are shaken out while the conveyors carry the hulls to a suitable store house. The hulls are used for cattle food. The meats are carried to the crusher rolls, through which they pass. These rolls break up oil cells to a large extent and leave the meats in a finely divided condition. From the crusher rolls the meats are carried to steam-jacketed kettles provided with agitators. There they are cooked to the proper point, which is determined by feel and smell. From the heaters the meats are dropped into cake formers, where they are formed into shape of cakes between camel’s hair press cloths in which they are placed in the heavy hydraulic presses which press out the oil. Good press-room work will give out 45 gallons of oil to the ton and leave in the cake between 6 and 7 percent of oil.
The crude oil as it leaves the presses varies in color from light sherry to deep claret. The variation is due to local conditions affecting the seed, also the manner of treatment in cooking. The flavor of the crude oil varies greatly in the different parts of the country. That made in Georgia and Carolina has a strong flavor of peanut, while that made in the Mississippi Valley and Texas has more the flavor of sweet Indian corn.
To prepare crude oil for edible purposes, it must go through a process of refining; this is accomplished by agitating in large tanks with caustic soda solution. When the soda is added in the proper amount, the coloring matter, free fatty acids, and vegetable matter contained in the oil are converted into a mucilaginous soap which separates in dark-colored flakes through the oil when heat is applied. When the granulation has reached the proper point, agitation is stopped, and the flaky soap stock settles at the bottom of the tank, leaving a clear, light, greenish-golden oil on top. The best practice allows tanks to settle about 12 hours, after which the soap stock has drawn off and the well settled yellow oil is removed to a settling tank where it is gently heated to remove moisture and remaining soap stock. This produces what is known as prime summer yellow oil. This oil has a sweet flavor and light yellow color. Unfortunately when used for cooking it gives off a very disagreeable odor and leaves a bad flavor in the article of food cooked with it. This renders further purification necessary. The oil is heated to temperatures varying from 150 to 200 degrees F. and agitated in kettles with fuller’s earth, after which it passes through filter presses, which remove the fuller’s earth and leave the oil very nearly white. In this condition the oil is still unfit for cooking purposes, on account of the peculiar flavor given by the fuller’s earth treatment, which is commonly removed by treatment with steam. Details of this deodorizing process vary and are regarded as trade secrets. The oil so prepared is largely used in the preparation of substitutes for lard and similar cooking fats. Such oil is a great improvement over the ordinary summer yellow and bleached oils, but falls short of being an ideal oil.
Within the last few years a cottonseed oil has been put on the market in which the objections to the use of cottonseed oil as food have been as nearly overcome as the chemical nature of the oil will permit. The oil produced by this process is practically odorless and tasteless and can be used satisfactorily for all culinary purposes. Large quantities are used by the bakers in place of lard. (David Wesson.)
Further Details.
—The cotton seed from various sources is put through a screen to take out the bolls and coarse material. The seed is then put through a gin to remove as far as possible any remaining lint, of which about 20 pounds per ton of seed are obtained. The clean seed is next sent to a huller composed of revolving cylinders covered with knives, which cut up both seed and hull. The chips are then conveyed to a screen placed on a vibrating frame, through which the kernels fall. The hulls are carried by an endless belt to the furnaces, where they are burned. The kernels of the seed are conveyed to crusher rolls, where they are ground to a fine meal. The meal is then sent to a heater, where it remains from twenty to forty minutes. These heaters have a temperature of 210 to 215 degrees F.
The hot meal is formed into cakes by machinery; these are wrapped in cloth and placed in the press. About sixteen pounds of meal are put in each cake. The cakes are placed in a hydraulic press, where a pressure of from 3,000 to 4,000 pounds per square inch is applied. The press is also kept warm. The expressed cakes contain only about 10 percent of oil. The cake is sold as cattle food or for fertilizing purposes. The crude oil as thus expressed contains about 1.5 percent of free acid, also a notable quantity of water and solid matters in suspension. The manufacture of cottonseed oil usually takes place in the winter months immediately after the ginning of the cotton is completed. The oil is likely to become rancid if kept unpurified until the hot months. The crude oil is collected in oil tanks at the press and shipped to the refining houses. In winter time when tanks are sent to the north where the temperature is very low the contents of the tank become solid unless protected from the action of the cold.
Fig. 57.—Removing the Oil Cakes from a Cottonseed Press.—(Courtesy of David Wesson.)
Refining Process.
—The first step in the refining of a crude cottonseed oil is to have it stored in large and deep tanks where it remains at rest for a proper length of time. During this period of rest the heavy mechanical impurities and water settle to the bottom of the tank and are typically known as “foots.” The oily portions of these fats are used in the manufacture of soap and for other technical purposes. The tanks may be connected with steam jackets in order to keep the oil at a proper temperature. During the process of deposition the oil is also treated with an alkali to neutralize the free acid which it contains. The precipitate formed by this process together with the principal part of the soaps produced are recovered with the “foots.” A solution of caustic or carbonated soda is one generally employed in this process of refining. If the admixture of caustic soda occurs at the time of filling the tank, the contents are kept well agitated for a sufficient length of time to secure an intimate mixture of the oil with the lye. Usually the deposition of the solid matter is accomplished in from two to three days. The supernatant oil is of a light yellow color, but not sufficiently pure to admit of being used for edible purposes. This yellow oil is treated again in a similar manner and allowed to settle a second time, or it is mixed with some substance which will facilitate the operation, and subjected to filtration by means of which a perfectly bright oil is secured. If, during this process, the oil has never been chilled so as to separate a part of its stearin, it is called summer oil, as an indication that it only remains clear during the hot weather. Oils intended for winter use are chilled before finally being put into packages, and the stearin which is separated at this low temperature is removed by filtration. The residual oil which is capable of remaining liquid at a low temperature by reason of the removal of a portion of its stearin, as above described, is known in the trade as winter oil. In this process of filtration fuller’s earth is frequently employed, which not only promotes the filtration but also absorbs and retains a large part of the color of the oil, which thus treated is almost colorless. Where cottonseed oil is used for mixing with lard it is highly important that it be practically free of color. When, however, it is used for mixing with oleomargarine the more yellow it is the more highly prized.
Extraction of Oil by Means of Petroleum.
—The light oils which are produced in the refining of petroleum and commonly called gasoline are typical solvents for fat and oil. Instead of extracting the oil by the pressure process, as described above, a practically complete extraction may be secured by successive treatments with the light petroleum oils. The principle of the process is exactly that of the extraction of sugar from sugar beets by hot water in the process of the manufacture of beet sugar. The cottonseed cake or pressed meal is broken into fragments of approximate size, placed in tanks, and treated with successive portions of light petroleum. The extraction is arranged in such a way as to be a continuous one, that is, the vessels for handling the oil cakes are arranged en batterie as in the case of beet sugar extraction. By this method all except a mere trace of the oil is extracted from the cake. The light petroleum oils are subsequently separated from the cottonseed oil by distillation and are used again in the process. There is little loss of petroleum oil. Where cottonseed oil is used for technical purposes there is no objection to this method of extraction, and much is to be said in its favor since greater yields of oil are secured. When used for edible purposes, however, petroleum extracted cottonseed oil is not of as high a quality as that extracted by pressure. It is difficult to remove all traces of petroleum, especially the odor, and there are constituents extracted by petroleum which are not mixed with the oil when it is separated by pressure. It is advisable, therefore, that cottonseed oil used for edible purposes be cold-press extracted and not petroleum extracted oil.
Standard for Cottonseed Oil.
—The official standards for cottonseed oil are as follows:
“Cottonseed oil is the oil obtained from the seeds of cotton plants (Gossypium hirsutum L., G. Barbadense L., or G. herbaceum L.) and subjected to the usual refining processes; it is free from rancidity; has a refractive index (25 degrees C.) not less than one and forty-seven hundred ten-thousandths (1.4700) and not exceeding one and forty-seven and twenty-five ten-thousandths (1.4725); and an iodin number not less than one hundred and four (104) and not exceeding one hundred and ten (110).
“‘Winter-yellow’ cottonseed oil is expressed cottonseed oil from which a portion of the stearin has been separated by chilling and pressure.”
Hazelnut Oil.
—The oil of the hazelnut is to a limited extent used for edible purposes. It is extracted from the seed of the hazelnut tree (Corylus avellana L). The seeds are very rich in oil and are said to contain from 50 to 60 percent thereof. The oil is almost free of stearin and is said to contain only about one percent. The rest of it consists chiefly of olein, there being but 12 percent of palmitin. While it is an edible oil, it is used chiefly in the manufacture of perfumes and as a lubricating oil. Its high price, however, excludes it from any general use, except for special purposes. Its specific gravity at 15 degrees is .916, and it absorbs about 86 percent of its weight of iodin.
Olive Oil.
—By far the most important of edible oils, both on account of its abundance and of its palatability, is olive oil. Olive oil has been used from the earliest historical times and probably was the first vegetable oil that was manufactured to any considerable extent in the early history of civilization. Its qualities have maintained for it a market among the nations of the world in spite of the fact that many other palatable and wholesome vegetable oils have been produced which, while not inferior in nutritive value to olive oil, are so very much cheaper that unless the olive oil possessed peculiar properties it would be forced out of the market. Its delicate flavor, extreme palatability, high nutritive power, and other general characteristics have maintained for it a market against the strongest competition.
Olive oil is procured from the fruit of the olive tree (Olea Europæa L.), and when it is to be used for edible purposes the method of extraction is by pressure. When olive oil is used for technical purposes, such as lubricating and the manufacture of soap, it is very commonly secured by extraction with a volatile solvent, such as petroleum. The olive is very rich in oil, the quantity varying from 40 to 60 percent. The quality of olive oil upon the market varies in a very great degree according to the country from which it comes, the degree of maturity of the olive from which the oil is extracted, the method of expression employed, and the character of the refining process to which the expressed oil has been subjected. Botanically, there are very many varieties of olive trees and thus nature would impart to the olive peculiarities due to the origin of the oil itself. The environment also has a great deal to do with the character of the olive and necessarily with the character of the oil produced. The olive tree flourishes best in semi-arid regions where the rainfall is not very abundant and the sunlight is not greatly obscured by clouds and the heat is reasonably high. The principal regions, at the present time, from which the commercial olive oils are obtained are Spain, Italy, Greece, southern France, and southern California.
Olives
1. MISSION
2. SEVILLANO
From Yearbook, U.S. Dept. of Agriculture, 1897
Adulteration of Olive Oil.
—By reason of its great value as an edible oil and its high price there is no one of the edible oils which has been subjected to such a systematic and extensive adulteration. By reason of the resemblance in general character of many of the edible vegetable oils to olive oil, adulterations of the most extensive character may be practiced without indicating to the eye any change in composition. Nearly all the edible vegetable oils have the light amber tint which is characteristic of many grades of olive oil, and the difference between the color of the olive oil and other edible oils is not greater than the difference between the tints of the various olive oils themselves. The connoisseur of extremely delicate taste is usually able to distinguish by the taste any given edible oil from olive oil. If, however, any given edible oil be mixed with olive oil in small proportions not exceeding 25 to 30 percent, even the skilled taster will be deceived. In such cases only the chemist who has much skill and practice is able to detect the adulteration.
Adulteration with Cottonseed Oil.
—In the United States the principal adulteration of olive oil is with cottonseed oil. This is an oil which has already been described as of high nutritive value and to which no objection can be made from any hygienic or dietetic point of view. It is made in great quantities in the United States, and when subjected to the most careful refining processes can be offered to the consumer at a price probably not greater than one-fifth that of high-grade olive oil. It becomes the ideal material with which to adulterate olive oil. This adulteration extends often to complete substitution, the oil in question, though represented as olive oil both by the dealer and the label, containing no trace whatever of that substance. Such bare-faced substitution has apparently almost passed away under the quickening ethical sense of the manufacturer and merchant and the character of the national and state laws. Many of the oils which are used to adulterate olive oil have a greater specific gravity, hence whenever the specific gravity of an olive oil at 15 degrees goes above .917 it is ground for suspicion of adulteration though by no means a positive proof. The presence of cottonseed oil in olive oil is easily detected by the Halphen test, which has already been described. In Europe a very common method of adulteration is with sesamé oil, the properties of which are described below. Peanut oil is also extensively used for the same purpose. These two oils are easily detected when mixed with olive oil. The sesamé oil is distinguished by the color reaction to be described. Peanut oil is distinguished by the saponification of the oil, separation of the fatty acids, and consequent crystallization of the arachidic acid, which produces a crystalline form which is readily recognized by an expert. Rapeseed oil and poppy-seed oil are also extensively used as adulterants in Europe, but not very extensively in this country. Nearly all the oils which are employed in the adulteration of olive oil have high iodin numbers, and therefore whenever an iodin number is above 89 or 90 it may be regarded as a suspicious circumstance. There are, however, many genuine olive oils which would be condemned as adulterated if this test alone were employed. In addition to the oils mentioned, small quantities of castor oil, lard oil, fish oil, and even of petroleum oil, have been found as adulterants in olive oil. These, however, occur very infrequently, and it is not likely that they have been employed in this country.
If the examination shows that a given sample is free of cottonseed, sesamé, and peanut oil, and other characteristics in the sample are those of olive oil, it may be safely accepted as a pure sample.
Color of Olive Oil.
—The color of the freshly expressed olive oil is usually green or dark from the chlorophyl and other coloring matter derived from the olive. When refined and ready for commerce the oil is of a yellowish-green tint usually. Sometimes the oil obtained from the first pressing is almost colorless, but as a rule an amber-green tint is observed in most of the commercial varieties. Lower grade oils are often decidedly green, but still edible, due to the admixture of chlorophyl from the green olive employed. The flavor of olive oil is a pleasant and agreeable one, but differs greatly in oils from different sources. The further north the oils are produced the less pronounced the flavor and the sweeter the taste. The more southern oils, such as are obtained in the south of Italy and Spain, have a stronger and more pronounced flavor which, however, is very much prized by those accustomed to it. Large quantities of olive oil are produced also in the French and other possessions in the north of Africa. These, however, have a stronger flavor than those produced upon the continent of Europe and are not so highly prized when used alone. Olive oil is almost free of stearin, being composed chiefly of olein with some palmitin. The amount of free acid in olive oil varies with the character of the olives employed and the age of the oil. On long standing, without becoming rancid, olive oil develops a large quantity of free acid. It is a common supposition that rancidity in an oil depends upon the development of free fatty acid, but this is not the case. If an oil be free of rancidity it may contain a large percentage of free acid without becoming inedible. It is not uncommon to find in olive oil as high as 3 percent or more of free acid. This is due to the fact that in the refining of olive oil alkalies are not usually employed, and therefore any free acid which the natural olive possesses is not neutralized by the alkalies, as is the case in the refining of cottonseed oil and some other vegetable oils.
Constituents of Olive Oil.
—Olive oil consists almost exclusively of olein and palmitin. There is very little, if any, stearin in the highest grade oil. If all the solid fatty acid at ordinary temperature be regarded as derived from palmitin, the quantity of palmitin may be regarded as varying from three to 20 percent, according to the origin and character of the sample. While the olein and palmitin, therefore, may be regarded as the principal constituents of olive oil, there are others, also, existing in smaller quantities. The quantity of free fatty acid varies very greatly in olive oil. It is highly important that the oil be separated from the pomace as speedily as possible, since any fermentation of the pomace increases the quantity of free fatty acid. The largest number of high-grade oils contain less than three percent of free fatty acid, but a larger quantity, as has been stated, does not render the oil inedible unless actual fermentation has taken place producing rancidity. Rancidity appears to be the result of the generation of other acids than oleic, and also aldehyds, formic, butyric, acetic, and œnanthylic acids have been found. Olive oil is a typical non-drying oil and therefore shows a less rise in temperature when mixed with sulfuric acid than other vegetable oils. The specific gravity of olive oil at 15 degrees may be placed at the average figure of .917. It sometimes falls as low as .912 and rises as high as .919. It absorbs from 80 to 90 percent of its weight of iodin. In some samples the weight of iodin absorbed is less, falling as low as 77 percent, but this is only in very extraordinary cases. Occasionally it goes above 90 percent. Probably the number 87 would represent about the mean percentage of iodin absorbed by most edible oils.
Method of Preparation.
—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.
Filter and thoroughly wash the precipitate with ether. Save the filtrate for the determination of the iodin number of the liquid fatty acids by the Muter method. The soaps on the filter are washed back into the flask by means of a stream of hot water acidified with hydrochloric acid. Add an excess of dilute hydrochloric acid, partially fill the flask with hot water, and heat until fatty acids form a clear, oily layer. Fill the flask with hot water, allow the fatty acids to harden and separate from the precipitated lead chlorid; wash, drain, repeat washing with hot water, and dissolve the fatty acids in 100 c.c. of boiling 90 percent (by volume) alcohol. Cool down to 15° C., shaking thoroughly to aid crystallization. From 5 to 10 percent of peanut oil can be detected by this method, as it effects a complete separation of the soluble acid from the insoluble, which interferes with the crystallization of the arachidic acid. Filter, wash the precipitate twice with 10 c.c. of 90 percent (by volume) alcohol, and then with alcohol of 70 percent (by volume). Dissolve off the filter with boiling absolute alcohol, evaporate to dryness in a weighed dish, dry and weigh. Add to this weight 0.0025 gram for each 10 c.c. of 90 percent alcohol used in the crystallization and washing if done at 15° C.; if done at 20°, 0.0045 gram for each 10 c.c. The melting point of arachidic acid obtained in this way is between 71° and 72° C. Twenty times the weight of arachidic acid will give the approximate amount of peanut oil present. No examination for adulterants in olive oil is complete without making the test for peanut oil.
The above process to be of any particular value can only be carried out by an experienced chemist, but the presence of peanut oil may be readily determined by any one who is experienced by following out the above process.
Where only small quantities of peanut oil are concerned, namely, not to exceed five percent, even in the hands of an experienced chemist, the above process may not lead to certain results.
Peanut oil is obtained from the peanut by the ordinary method of hydraulic pressure. The first cold pressing furnishes the oil of finest character for edible purposes. Subsequent pressures or pressure with heat furnish an additional supply or a great quantity of oil but not of the same palatability. Peanut oil is highly prized as a salad oil either alone or mixed with other oil, notably olive oil and sesamé. The oil is purified by a large settle and by filtration and by the processes usually practiced with other oils of vegetable origin. The oil is easily and completely digested and furnishes an abundant source of heat and energy to the system. The number of calories produced by the combustion of one gram of oil, either by ordinary burning or by oxidation in the body is about 9,300.
The cake which is left after the pressing out of the oil is very highly nutritious, containing still considerable quantities of oil, the whole of the protein matter, and other digestible solids of the nut.
As before stated, it is extensively used as cattle food and as fertilizer. It may also be ground to a meal and used as human food, but furnishes an unbalanced ration in which the protein is far in excess.
Rape Oil (Colza Oil) (Brassica campestris L.).
—There are different kinds of oil which belong to the general class which is known as rape oil or rapeseed oil. The different kinds are derived from different varieties of Brassica campestris. The English names of the three most important varieties are—(1) colza oil, derived from the seeds of Brassica campestris; (2) rape oil, derived from the seeds of Brassica napus L.; (3) rübsen oil, derived from the seeds of Brassica rapa L. The character of the oil also varies according to the manner of its extraction. The first pressings from the cold powdered seeds is of a finer quality for salad purposes than the heavier later pressings from the hot seeds. The oil is also sometimes chilled and the crystallized stearin separated in order to keep it in a liquid state during the winter time, so that the winter and summer varieties are sometimes recognized in trade. There is, however, no difference in the other characteristics of the oil.
The specific gravity of rape oil at 15.5 degrees C., compared with water at the same temperature, is about .916. The variations from this mean number are not very great. Rapeseed oil absorbs almost its exact weight of iodin,—the average iodin number being not far from 99.
The Chief Adulterations of Rape Oil.
—The chief adulteration of rape oil consists in the admixture of cheaper or flavoring oils. Among those which are often used in the adulteration of rape oil are linseed oil, hempseed oil, poppy-seed oil, chamomile oil, cottonseed oil, the various mustard oils, refined fish and blubber oils, rosin oil, and paraffin. Some of these adulterations, it is seen, cannot be added to rapeseed oil when used for edible purposes. The chief adulteration of rapeseed oil, when intended for edible purposes, is the addition of cottonseed oil. The detection of these various adulterations, with the exception of that of cottonseed oil, can be accomplished only by an expert chemist. The presence of cottonseed oil can be detected by the application of the Halphen test already described.
Technique of Extraction.
—The extraction of oil from the rape seed is not different from that of other oily seeds. It is either extracted by pressure, which is the proper way always when it is to be used for edible purposes, or when used for technical purposes it may be extracted by means of carbon bisulfid or petroleum ether. When extracted by pressure for edible purposes the oil should be refined by a similar treatment to that applied to cottonseed oil and finally filtered, preferably after mixing with fuller’s earth or other similar material, in order that it may be perfectly pure and bright and free from suspended matter which interferes with its utility as an edible oil.
A very common treatment of the expressed oil, in order to coagulate and separate the mucilaginous matter which it contains, is with sulfuric acid. This acid has the very valuable property of coagulating this class of bodies. When treated with sulfuric acid it is necessary that the oil be thoroughly washed many times in pure water in order to remove the last trace of the acid.
The residue or oil cake is prized as a cattle food or as a fertilizer. The average content of oil in rape seed is about 37 percent.
Sesamé Oil.
—Sesamé oil is very commonly used for salad oil and for the other purposes to which the edible oils are devoted. It is also known as gingili oil and teel oil. Sesamé oil is obtained by pressure from the seed of the sesame plant,—Sesamum orientale L.
Sesamé oil possesses a light amber color when properly made, is free from any unpleasant odor, has an agreeable taste, and when expressed cold produces what is known as the cold-drawn oil which is regarded by many as of equal palatable value with olive oil. Sesamé oil, in addition to containing stearin, palmitin, and olein, also contains a small quantity of a glycerid which exists in large quantities in flaxseed oil, namely, linolein. When prepared for edible purposes it contains only a small quantity of free acid, is free from rancidity, clear, and brilliant in appearance and has a sweet agreeable taste. The specific gravity of sesamé oil at 15 degrees C. varies from .9225 to .9237. It absorbs from 103 to 108 percent of its weight of iodin and has a refractive index at 15 degrees of about 1.4748.
Adulteration of Sesamé Oil.
—Some of the other vegetable oils are cheaper than sesamé and are added to it for the purpose of adulteration and cheapening the product. Among the most common oils used for the adulteration of sesamé are poppyseed oil, cottonseed oil, and rape oil. The presence of cottonseed oil in sesamé oil is easily distinguished by the Halphen test already given. The presence of poppyseed oil is revealed by the high iodin number and the high degree of heat produced when mixed with sulfuric acid.
Only the best variety of cold-drawn sesamé oil is used for edible purposes and for making oleomargarine. The inferior qualities are used in soap making, the making of perfumes, etc., and the lowest quality of oil is used for burning purposes.
Characteristic Reaction.
—A test which is known as Baudouin’s is extremely delicate and reliable and is easily applied. It consists in the development of a red color when a small quantity of sesamé oil is treated with hydrochloric acid in the presence of furfural. The test is easily carried out as follows: Place a few drops of a two percent solution of furfural in a test-tube with 10 cubic centimeters of sesamé oil or the oil to be tested for sesamé and 10 cubic centimeters of hydrochloric acid of 1.19 specific gravity, and shake the mixture well for half a minute. When the tube is left at rest, if sesamé oil be present the aqueous acid layer which forms will have a distinct crimson color. Any coloration which is produced by other oils is entirely distinct from this one and therefore can be easily distinguished.
Geographical Distribution.
—The sesamé plant is grown chiefly for commercial purposes in India, China, Japan, and West Africa. The technical preparation of the oil, in so far as is known, is not practiced in the United States. It is pressed and prepared for commerce chiefly in France. The seeds are rich in oil, yielding a larger percentage by pressure or extraction than most of the oil-bearing seeds.
Sunflower Oil.
—The oil extracted from the seed of the sunflower is of high quality for edible purposes. Although not in general use in this country, it is very extensively used in Russia and some other parts of Europe. There is every reason to believe that a profitable industry could be established in the preparation of edible oils from sunflower seeds. The plant grows in the greatest luxuriance in nearly all parts of the country, and the yield is sufficiently great to make it an object of more interest to our agricultural population than it is at the present time.
The oil is obtained from the seed of the sunflower (Helianthus annuus L.). It is of a pure amber tint with an agreeable odor and pleasant taste. As has already been said it is grown largely in Russia and also in Indo-China. The seeds are very rich in oil. Before expression the hulls should be removed, since these form a porous substance, and if the seeds are crushed with the hulls large quantities of oil are absorbed and cannot be recovered.
The method of preparation is the same as that for other edible oils, the kernel, after the removal of the hull, being ground and cold-pressed for the highest grade. By heating and renewing pressure lower grades of oil are secured suitable for soap making. Where all the oil is required the extraction with bisulfid of carbon or gasoline is advised. Such oils, however, are not suitable for edible purposes because of the difficulty of removing the last traces of the solvent. The specific gravity of sunflower oil at 15 degrees is approximately .925. It absorbs a very high percentage of iodin, and in this respect it may be classified with the drying oils. Its iodin number ranges from 120 to 130. No specific color reactions have been established by means of which sunflower oil may be readily distinguished from the other edible oils.
In fact sunflower oil has not been subjected, by any means, to as critical a study as many other vegetable oils.