The Olive Its Culture in Theory and Practice/Chapter 12
Extraction, Storage and Clarification of the Oil.
CHAPTER XII.
Psalms 104 vs. 15.
A short quotation from the distinguished Prof. Cupari, of the University of Pisa, will give a clear idea of what is somewhat inaccurately called oil making, and correct a common error in regard to the process. He says, in his lesson on agriculture, "Olive oil is not like the juice of the grape, which requires a chemical process to transform the sugar it contains into alcohol, in order that it may become wine; the oil is there, ready made within the fruit, and the utmost that can be done is to extract it, just as it is, bursting the cells within which it is enclosed, by crushing the olives and then pressing them." "Olive oil is found, not made."
One may fail to extract it, one may injure it in the process, it may lose in quality or even become rancid by careless handling or storage, but the one and only object of the oil mill is to extract, clarify and store the oil, while experience and skill will undoubtedly add much to the result of a given olive harvest, the fact remains that the oil is made and in the berry. A mortar and pestle will crush olives and the oil and water can be strained out, through cloth or crash by hand. The difference is not of process but of quantity to be dealt with. This should be clearly understood in California, as this interest grows. It is not beyond credence that the happy possessor of a few producing olive trees would be willing to devote the time and labor necessary to extracting his own oil for household use, with the simplest of home machinery and especially when the physician tells him the value of olive oil as both medicine and food; and the gourmet of the many additions it may make to the home menu; while the analyst warns him of the detected adulterations not merely of so called imported oils, but of adulterations passed off on the community as "California olive oil."[1]
The analysis of the berry shows the following result:
| OIL | WASTE | |||||||||||||||||||
| Pulp 75.02 | Water | 51.25 | ||||||||||||||||||
| Fibre | 14.38 | 14.38 | ||||||||||||||||||
| Oil | 9.39 | 9.39 | ||||||||||||||||||
|
The following is the chemical analysis of the olive:
| Potash | 57.336 |
| Soda | 5.170 |
| Lime | 5.115 |
| Magnesia | 0.130 |
| Oxide of Iron | 0.305 |
| Chloride | 0.111 |
| Phosphoric acid | 0.929 |
| Sulphuric acid | 0.533 |
| Siliceous acid | 0.356 |
| Carbonic acid | 29.985 |
| 100.000 |
THE COMPOSITION OF OLIVE OIL.
| Stearine C.17 H.110 O.6 |
Palmatin C.51 H.98 O.6 |
Oleine C.57 H.104 O.6 | |
| Carbon | 76, 6 | 75, 9 | 77, 4 |
| Hydrogen | 12, 4 | 12, 2 | 11, 8 |
| Oxygen | 11, 0 | 11, 9 | 10, 8 |
| 100, 0 | 100, 0 | 100, 0 |
The oil of the pulp is rich and of a delicious flavor, that of the stone is dark and cloudy, that of the seed contains essential oil, while the skin in its little cells contains an essential and resinous oil in small quantities. These oils of stone, seed and skin, far from adding to the oil of the pulp, would be a serious injury if not in such small quantities. From this it is obvious that in cultivating olives for oil, the varieties with much pulp and proportionately small seeds, should be selected, as is always done in the true oil countries. The proportion of oil to berry as given by reliable authorities runs from ten to twenty per cent. in weight.
The Messrs Rae of Leghorn, olive oil exporters, in their pamphlet on the olive, give fourteen to twenty per cent. and eighteen to twenty for the finest oil varieties. Mr Cooper's best result as given, was ten and twelve per cent. Mr Ludovico Gaddi, and the agricultural manager at Santa Clara College, as well, estimate that forty pounds of berries will produce one gallon of oil, which is about eighteen per cent.; but this of course refers to well dried berries.
It should be said that California olive culture is so comparatively recent and limited, that reliable statistics can hardly be expected. But it may be safely asserted that certain exaggerated statements which have appeared in print, as to percentage of oil to berries, will not be verified even in this exceptional soil and climate.
In view of the fact that the processes of the oil mill, are singly to "extract" the oil, the clarifying, whether by simple deposit or by passing the oil through refining material, being but a part of the general work of separating the oil from the solid and watery parts of the berry, it is evident that unless some mechanical difficulty renders delay necessary or convenient, the berries will yield a better oil if this be extracted immediately or very soon after their gathering. That this is true is now admitted by all writers of value, and by all manufacturers of the fine grades of oil. The belief that olives retained for long periods in the store house produce as good an oil, and much more than the freshly worked—a belief held by the rustics in the times of Cato and Columella, and controverted by both these writers—still holds its own among the more ignorant peasants and notably in Spain, where olives are often stored for months and occasionally for a year.
Again, the immediate extraction within twenty four hours as advised by Messrs Rae as the best usage of Tuscany, will not always be possible as such a complete system demands very abundant facilities of machinery and labor. No one who has engaged in oil extraction will be inclined to deny that the process is, at least, somewhat more difficult with absolutely fresh olives. While the immediate expression of oil is undoubtedly the best system, and growing in favor and practice, it must be admitted that, in all probability the greater proportion of olive oil and even the higher grades of oil are made after the olives have been partially dried. The question is, how to avoid any danger to the olive, if drying is found necessary or convenient. The purpose of drying is to remove as much of the water of the olive as possible. Evidently any tendency to softening will be simply the beginning of decay and will injure the quality of the oil, and any possibility of mould must be avoided.
The Italian system is to spread the freshly picked olives on floors of porous brick, not more than five inches deep and allow free passage of air above them, while two or three times a day, they are carefully and gently raked over. If drying is decided upon, or the olives must await manufacture, this is the simplest and safest way for a natural process.
Mr Ellwood Cooper of Santa Barbara has adopted a system of artificial drying of his own invention, similar to fruit dryers, which he has described in his work on olive culture and which he finds satisfactory. Naturally this avoids certain difficulties in fresh pressing and certain dangers in natural drying.
The first process of the oil mill is the crushing of the olives. The crushing machine generally used, consists of a circular tub or trough of stone or bricks covered with cement, having a stone floor on which revolves a heavy stone wheel on an axle, one end of which is attached to and works on a pin or pivot set in the center of the trough. This mill wheel crushes and grinds as it rolls over the olives, which are constantly pushed by a scraper into its path. This may be worked by hand, by horses, or oxen, by steam or water power. The stone should be non porous lest it absorb oil which may become rancid.
The size of the crusher will vary with the needs of a given mill. Presses are of various kinds. The Italians, Spaniards and French generally use a screw press (descending.) This may be worked by hand, by horse or ox power, by water or steam. In any case the pomace is put into sacks of jute called "bruscole," which are then piled up, eight, ten, or a dozen high, or into a steel cage with or without crash to contain it, and placed under the descending screw of the press.
Mr. Cooper uses a beam press such as is used in cider making. The pomace is held in place by wooden crates and Russian crash. He suggests the oleomargarine press as probably the best for olive oil expression. In both Italy and Spain powerful hydraulic presses are used either with the jute sacks or the iron cage. They are similar to the hydraulic presses of the wineries, and in fact these latter can be used for oil extraction.
The objection to the hydraulic press is, that with it one runs the risk of suddenly applying too great pressure and what is needed in expressing olive oil is not sudden, but gentle and constantly increasing pressure. If the pomace of olives is suddenly subjected to extreme pressure, no oil at all will flow; for this reason hydraulic presses have been altogether abandoned in some parts of Spain, as in ignorant hands they did not give satisfactory results. The great advantage of the beam press is, that it is impossible to apply the pressure in any other way but by a steady and gentle increase, as more weight is placed on the end of the beam. But after all, in intelligent hands the hydraulic press is preferable, for if it is properly used, the amount of pressure required may be exactly graduated. In the first pressure, usage differs as to the employment of water. It must be clearly understood, that the olive berry contains a large amount of water from which the oil separates itself when the mixed liquid is allowed to rest after the expression, and that the employment of water is not for an adulteration, or other improper purpose, but simply to free the oil and water in the berry and ease the process of pressing. Doubtless oil extracted without the use of water is appreciably finer to an expert "olive oil taster," but it is doubtful if very much of such oil reaches the market. The usage of mills differs. The most extreme divisions of oils would be, that of the first crushing and the first pressure; that of the same pomace crushed a second time; that of the same pomace treated with cold water; that of the same pomace treated with hot water; that of this pomace ground fine, placed in an agitator and heated with water, until the stones fall to the bottom and are carried away, and the water and lighter matter passed into settling tanks, where the oil is skimmed off, while a little more is made by another pressure; this is called washed oil. This same pomace instead of being treated as above, may be treated by the bi-sulphate of carbon process at special factories, with a larger percentage of oil as a result. Finally a low grade of oil is skimmed from the water used in collecting the oil, and which is carried out of the mill and deposited in tanks called from the low quality of the oil, "the inferno."
The term "Virgin oil" is used so variously, that it is difficult to define it with accuracy. It is used for the first run of oil whether made with or without water; it is also sometimes used for early oil—the first of the season; the most exact use seems to be the oil which flows either without any pressure by the weight of the pomace in the racks or the cages, or just as the pressure begins to tell. Watching the press one sees pure oil and water run out, and if this is taken from the receiver at once, the oil and water separate quickly, and the oil is exceedingly rich and fine. As the pressure goes on the liquid becomes tinged with purple from the coloring matter in the berry.
Admitting the definition as correct, we should have five possible qualities of palatable oil, and two, suitable only for manufacturing purposes. It is unnecessary to say that Virgin oil as defined above is not an article of trade. A little is probably made on large estates, for the proprietors, and for their friends consumption, nor is it necessary to say, that the four possible edible oils are reduced to two or three.
If a run is made without water, the second run will probably be made with hot water, or two runs without water and then the hot water or with cold water at once, and then hot water. Cold water is not injurious, but oil gathered by the hot water process is not as fine, and does not keep as well as that expressed without water or with the use of the cold. Extreme heat is dangerous to oil at all stages of expression and storage; and for this reason Italians doubt the safety of artificial drying even where they consider drying necessary or advantageous. After the expression of the oil, it separates from the water and small particles of the berry which have passed the sacks or cage, and rises to the surface, when it is carefully skimmed off and placed in other vessels to settle; thence drawn off again from the surface, and clarified by being passed through a layer of filtering cotton, filtering paper, or even bone charcoal. It is then fit to place in the storage receptacle. During the process of crushing, pressing, depositing and clarifying, too extreme cold chills the oil and checks its flow and clarification, and in cold weather it is desirable to have moderate artificial heat in the mill. When clarified, the oil should be put in a cool place, and in cool receivers, of which tanks of tiles, brick lined with marble, or glass, and the Italian glazed terra-cotta lined tanks are the best. The Italians use wooden tanks lined with tin and also brick tanks lined with a fine cement. Wood is not desirable, the oil which soaks into it is liable to turn rancid. Again wood alone, lacks the coolness required, at least in an Italian summer. A sufficiency of pure water and extreme cleanliness, are essentials of oil production for table use. Not only must the water used on the pomace be pure, but all the different parts of the machinery must be kept clean by constant washing, and mere water is not sufficient. The best cleaning method seems to be, washing with hot water and soda (1½ ounces to a gallon of water) then, with fresh hot water remove the soda, and finally rinse out well with cold water. These washings must be frequent and careful, of machinery crusher, press, sacks, cage and crash, receiving vessels, and everything with which the oil comes in contact. Smoke from fires must be prevented, and smoking must be forbidden in the mill, oil takes a taste very readily, and the mill should be at a distance from barn and stable. It is a common thing in old Italian mills to have the horse power in the mill. This is of course very undesirable.
The alterations to which olive oil is subject are various, and although numerous cures have been suggested, no remedy has ever yet been successful when once the alteration has commenced. Sometimes the disagreeable taste can be so disguised that it is not perceptible to the consumer; but that is only a temporary expedient, and cannot be termed a remedy. The most dangerous as well as the most common of the maladies to which olive oil is liable are:
Natural Rancidity.—This can be imparted not only by the carelessness of the maker, or by the uncleanliness of the utensils used in making, or storing the oil, but also through the nature of the soil in which the trees are growing. If the earth is very rich, and the growth of the trees is exceedingly rank or strong, this forced vegetation will produce fruit that will impart a peculiar taste to the oil, which will at once be detected by a delicate palate, and in a short time it will become so rancid that its market value will be greatly depreciated.
Taste of the Worm.—This is only observable when the fruit has been attacked by the Dacus oleæ. Sometimes the oil is so injured that it can only be used for industrial purposes.
Dry Taste.—When a very dry season occurs, with frequent and intensely hot winds, the growth is checked, the stem of the fruit is dried, and the berries get hard, dry, and shriveled. In this case the oil acquires a peculiar woody flavor, which, however, is not detected by all consumers.
Acquired Odors.—The oil will most readily absorb any odor to which it may be exposed, and when this is derived from tobacco smoke, onions, manure, etc., it greatly deteriorates its value. A smoky chimney in the neighborhood of the room where the oil is being made, or any lack of cleanliness, will injure the oil greatly.
Taste of the Cask.—This can be transmitted either by the vessels in which the oil is placed, if not made and kept scrupulously clean, or by contact with the tools and other appliances used in making it.
Absolute Rancidity.—Many things contribute to rancidity in olive oil, such as excessive heat, contact with the air, want of regular racking, contact with metals that can be dissolved by the natural acids of the oil, and other causes too numerous, and not of sufficient importance to mention.
It hardly seems possible to exaggerate the importance to the United States of olive culture as an added agricultural interest, productive of an article of such high value for medicinal use, and of such varied benefit as food, both in the every day dishes of a family table and the luxurious plats of the artistic chef.
While California is the most favored of the United States for the culture of the olive, there is a large Territory besides capable of it, and, although the home demand will probably grow even more rapidly than the production, it seems safe to assert that pure olive oil can be produced in the United States with profit, at a price so reasonable as to put it on the list of our exports. Olive culture is still in its infancy, but it seems as if the time had fully arrived for its importance to be recognized by National and State Government, and indeed the Agricultural Department at Washington has commenced its study. As a culture it is one of the most ancient, and the experience of the old countries must be of great value in the development of an extensive olive interest here. What might not be the value to this State of the knowledge, skill, and experience of a trained expert on the culture of the olive and the processes of oil expressing, if the services of such a one could be secured for a sufficiently extended time to allow of a fair application of his knowledge to the new country, soil, climate and conditions! Certainly such an experiment would be less costly in the end, and more satisfactory, than any attempt to send an American abroad to study the culture. It is more than probable than in many places the variations of conditions of climate and soil may compel deviation from the standard methods of other oil countries as the interest develops, and still it is necessary to know their rules, the result of so many years experience. Considering the wonderful adaptability of the American mind to the new, and its tendency to improve methods and processes where invention can suggest more convenient ways or labor-saving machinery, we need not fear to prophecy some great advance in olive culture and in oil producing processes as they become American interests.
THE END.
- ↑ See the late statement by the Horticultural Society of the adulterations practiced in San Francisco.—Pacific Rural Press, July 7th, 1888.