Primitive and Modern Processes of Extracting Cod-Liver Oil
from "Cod-liver Oil and Chemistry," by F. P. Moeller, Ph.D.
Bulletin of Pharmacy, vol. 9, no. 5, page 216, (May 1895).
The Liver.—Before entering upon the details of the modern methods of preparing cod-liver oil, it will be well to give a brief description of the source of the oil-the liver of the codfish. In size the livers vary considerably, but their average weight may be stated at a little over half a pound, as, taking one year with another, a hectoliter contains about four hundred livers, weighing about 220 lbs. A liver of that weight, with its fiaps extended, is about 14 inches in length and about 2½ inches thick at the central part. The liver of the codfish, when healthy and fat, is cream-colored, and so soft that the finger may be pushed right through it without any effort. The leaner the liver the tougher it is, and its color deepens to a reddish or even to a nearly black hue. There are always a certain number of diseased livers to be found amongst the healthy ones. These are recognizable by the presence of colored spots, or by their being wholly or partly of a green color. Such livers ought never to be employed for making medicinal oil; but manufacturers who compete for cheapness cannot well afford to reject them, as their percentage is such as to form a considerable item in the manufacturing account.
Crude Methods of Preparing Cod-liver Oil in Norway. —The primitive method, which is still used to a certain extent, is as follows: As soon as the fishermen finish separating the livers and roes, they sell the fish and carry the livers and roes up to their dwellings. In front of these are ranged a number of empty barrels, into which the livers and roes are placed, separately of course. The fishermen do not trouble to separate the gall-bladder from the liver, but simply stowaway the proceeds of each day's fishing, and repeat the process every time they return from the sea until a barrel is full, when it is headed up and a fresh one commenced. This is continued up to the end of the season, when the men return home, taking with them the barrels they have filled. The first of these, it may be noted, date from January, and the last from the beginning of April; and as the fishermen on arrival at their homes have many things to arrange and settle, they seldom find time to open their liver barrels before the month of May. By this time the livers are, of course, in an advanced stage of putrefaction. The process of disintegration results in the bursting of the walls of the hepatic cells and the escape of a certain proportion of the oil. This rises to the top, and is drawn off. Provided that not more than two or three weeks have elapsed from the closing of the barrel to its being opened, and if during that time the weather has not been too mild, the oil is of a light yellow color, and is termed raw medicinal oil. As may be supposed, however, very little oil of this quality is obtained; indeed, as a rule there is so little of it that the fishermen do not take the trouble to collect it separately. Nearly all the barrels yield an oil of a more or less deep yellow to brownish color; this is drawn off, and the livers are left to undergo further putrefaction. When a sufficient quantity of oil has again risen to the surface, the skimming is repeated, and this process is continued until the oil becomes a certain shade of brown. The product collected up to this point is known as pale oil. By this time the month of June has generally been reached, and with the warmer weather the putrefaction is considerably accelerated, and the oil now drawn off is of a dark brown color and is collected by itself. It is rather misleadingly called light brown oil. When no more can be squeezed out, the remainder is thrown into an iron caldron and heated over an open fire. By this process the last "rests" of oil are extracted from the hepatic tissues, which float about in the oil like hard resinous masses, termed Grau, and used as manure. In order to fully carry out the extraction, it is necessary to raise the temperature considerably above the boiling-point of water. This is well shown by a simple test frequently employed by the fishermen who, in order to ascertain if the requisite heat has been attained, squirt a small quantity of water into the oil, and if it has reached the proper temperature the water is instantaneously converted into gas with an explosive-like noise. The oil prepared in this way is very dark, almost black, and with a greenish fluorescence in reflected light. In thin layers and by transmitted light it shows a brown color, and is therefore termed brown oil.
Not all the fishermen, however, prepare the oil themselves. Most of them, in fact, are compelled to sell the livers to the shop- or store-keepers, who supply them with such goods as they and their families require. The reason for this is the system of credit which in these regions has developed almost into a science. The method works somewhat as follows: The local storekeeper supplies the fisherman with whatever he wants, and he, in return, undertakes to deliver all the proceeds brought back by him from Lofoten the next year. The store-keeper, again, is also supplied on credit by a merchant at Bergen, and on exactly similar conditions. He must bind himself to send to the merchant all he has to sell, and he is not allowed to stipulate any price for his goods. The prices are determined by the merchants of Bergen, who are the real controllers of all this credit system. They meet together at intervals and fix the prices to be paid for the produce received, having proper regard to the state of the market and, of course, an eye to their own profit. This system works so beautifully that the fisherman who has once got into the grip of the store-keeper can seldom emancipate himself, nor can the store-keeper in his turn free himself from the control of the merchant.
In this way the store-keepers are enabled to collect the cod-livers from great numbers of the fishermen, and as a consequence they supply by far the largest amount of the raw medicinal oil which comes into the market. The store-keepers and fishermen send almost all their products to Bergen, which is, therefore, the great emporium for cod-liver oil, but none is manufactured there. When the oils reach Bergen they are set aside for a time in order to allow water and impurities to settle. When this has been completed the oil is drawn off, and such as happens to be deficient in the properties qualifying it for one of the four classes above mentioned is boiled, mixed and manipulated until it has acquired those properties. Sworn sorters, who are appointed by the City of Bergen, may be called in to decide disputes as to the quality of an oil. They are not bothered with any scientific knowledge, but simply carry out their analysis of an oil by dipping their finger therein, conducting it to the olfactory test organ, and then to the gustatory ditto. This, in their opinion, is the alpha and omega of a careful and exhaustive analysis, which being made, they proceed to pronounce judgment. As long as they keep within the legitimate limits of knowledge gained by actual experience, their decisions may be fair enough. Sometimes, however, they affect to understand more than any experience of this sort can teach, and then the decisions they give pass from the useful to the ridiculous.
The new method of preparing cod-liver is, like most inventions, a very simple matter—after it has been invented. It is now generally known as the "steam process," and the essential difference between it and the older methods is that the oil pure and simple is extracted from the livers, instead of the oil mixed with a great number of decomposition products. It was these decomposition products that gave the oil what was supposed to be its characteristic brown color and far from delightful smell and taste. They were derived from the putrefaction of the albuminous constituents of the liver, and it was very natural that they should be supposed to be part and parcel of the oil when that was obtained by leaving the livers until, by putrescence, the hepatic cells were broken up and the oil globules in them allowed to exude. The introduction of the steam process, however, showed that these products of putrefaction were not an essential constituent of cod-liver oil from the chemical point of view; and from the therapeutical, subsequent experience has shown that they have nothing to do with the beneficial action of the oil, if, indeed, they do not detract from it. It may be asked whether, apart from color, taste, and smell, it is a desirable thing indiscriminately to add the ptomaines produced by the putrefaction of albumen to any medicinal remedy whatsoever.
When, therefore, the steam process is carried out with proper regard to its essential principle, the livers must be used absolutely fresh; indeed, if over twelve hours are allowed to elapse after the capture of the fish, no first-rate oil can be produced from their livers. As soon as the livers are landed, they should be carefully sorted, and all poor, small, bruised and diseased specimens thrown aside. Those finally selected should be thoroughly cleansed from blood, membrane, and other impurities, by washing in several waters, and then, after the gall-bladder has been severed, they should without delay be deposited in the melting-vessels. There are three different ways by which the melting operations can be carried out. The original method was to heat the livers upon a water bath of large dimensions. The apparatus required for this is now manufactured wholesale in Norway. It is made of tinned iron sheets, and may be purchased for less than £10, a price that places it within the reach of every one, and that to a large extent explains its almost universal use. It is, of course, somewhat difficult to state the minimum length of time which manufacturers allow for heating the livers, but from hearsay and personal knowledge we believe it is generally from two and a half to three hours. When the livers have been exposed to this heating process for such a length of time as the manufacturer thinks profitable, the oil is drawn off and filled into barrels. The remainder, a thick, pulpy mass, is known as Graxe, the liver rests. By some it is put into bags and pressed, but so quickly does putrefaction ensue that the oil obtained in this way is dark in color, similar to the light brown or brown oils, and possesses a very rank, unpleasant odor, which is increased with the least delay in the pressing operation. Some manufacturers, therefore, simply shoot the pulpy mass into the sea without attempting to get more out of it, even though the oil it contains amounts to 9 or 10 per cent. of the original weight of the livers. When the liver rests are pressed and the oil is extracted, there remains a dry, compressed mass which is generalIy either thrown away or sold to fish-guano manufacturers. Even this contains oil to the amount of 25 per cent. of its own weight; but that oil cannot be obtained by mechanical means, and its extraction by other methods would be too expensive to be profitable.
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