Cod Liver Oil
Notes on the Manufacture of
Our Most Important Dietary Supplement

By David Wetzel

When I began my quest to market cod liver oil, the biggest hurdle I had to overcome involved the myths and inaccuracies that are discussed in the market place. After 18 months of research, I was comfortable placing my first order.

Eighteen months after making that first order it became apparent that to do justice to my efforts and to my customers, I needed to do a close-up, first hand study of the industry, including the harvesting and processing of raw materials and the various processing techniques to extract and purify the oil. I needed a full and unabridged understanding.

I have interviewed manufacturers, laboratories, fisheries, fish meal plants, fish farms and many fish oil mills throughout the world. The final phase of my work included a careful study of the facts to select a region of the world that offered the largest and most modern fish oil industry and then a personal visit and inspection of the various enterprises.

The culmination of my research was two weeks spent in Iceland and Norway visiting six different mills, a cod fish farm, fishing boats and a slaughter house.
COD LIVER OIL BY THE GLASS?

The Arctic explorer and anthropologist William Stefansson reports in his book Not By Bread Alone that “There are European districts where certain oils are drunk in limited quantities. For instance, Scandinavian fishermen often have a belief in the nearly magical value of cod or halibut liver oil, and some of them will toss off, most likely in the morning, the equivalent of a wineglassful.” Among the Eskimos, however, “Nobody drinks large swigs of oil.”

But the Eskimos did use seal oil in prodigious amounts. According to Dr. Price, “Seal oil provides a very important
part of their nutrition. As each piece of fish is broken off, it is dipped in seal oil.” He noted that the Eskimos preserve foods like berries and sorrell grass in seal oil. “I obtained some seal oil from them and brought it to my laboratory for analyzing for its vitamin content. It proved to be one of the richest foods in vitamin A that I have found.”


MEET MR. COD

The cod family (Gadus sp.) is one of the largest and most successful families of fish, found in all oceans of the world. There are more than 90 species of cod, of which 40 are commercially available as oils.

Even in the same waters, different species of the Gadus family can have great a variation in fatty acid profile and vitamin A and D content. In Norway, the species that produce the greatest concentrations of A and D are Gadus virens and Gadus pollachius. Their oils contain as much as to 5000 IU vitamin A and 500 IU vitamin D per gram. (That’s 25,000 IU vitamin A and 2500 IU vitamin D per teaspoon!).These two varieties are common in waters off the Shetland Islands. At the other extreme is Gadus gadiculus thori, which produces 500 IU vitamin A and 50 IU vitamin D per gram of oil—just one-tenth as much. This species is found close to the shores of Norway.

Cod also grows in fresh waters. The Great Lakes are host to a species of fresh water cod called burbot or “lawyers,” which tests carried out during the 1940s indicated to be a very rich source of vitamin D. Unfortunately, the Great Lakes fresh water cod has received little interest since then, and most recreational fishermen consider the burbot a nuisance fish.

The great difference in levels of fat-soluble vitamins is due principally to differences in enzymatic liver activity in the various cod species. Within the same species, feed, age and location will account for additional variations in the nutrient profiles of the oil.

Cod liver oil provides not only vitamins A and D, but also valuable fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). As with vitamins A and D, levels of EPA and DHA vary according to the species and the temperature of the waters in which they dwell. For example, Gadus morua from the Atlantic typically provides oil containing 8 percent EPA and 12 percent DHA while the same species in the Baltic Sea provides 9 percent EPA and 20 percent DHA. Another species, Gadus merluccius, typically has 17 percent EPA and 10 percent DHA.
THE CHANGING MARKET
FOR COD LIVER OIL

Today, standards set by the United States Pharmacopeial Convention limit the level of A and D in cod liver oil to 2500 IU and 250 IU per gram respectively. EPA must fall in the range of 7-16 percent, and DHA in the range of 6-18 percent. One mill described this narrowing of definitions as a restriction on the market and opportunities, resulting in a tightening up of the market supply, as it excludes some species of cod that fall outside the EPA and DHA range of the specification. Many of the cod that fall outside the EPA and DHA guidelines are the species with higher vitamin liver oils. Two other market forces are likely to have an effect on the price and availability of good cod liver oil. One is the increasing demand and profitability of supplying fresh cod livers to the Eastern European market. These folks still understand the value of cod liver, and as their prosperity grows, so will their consumption of this nutrient-dense food.

The other force that is likely to cause fundamental changes in the cod liver oil market is the growing emphasis on ultra-clean fish oils along with a focus on fatty acids rather than natural high-vitamin content.
COD FARMING?

In my opinion, farmed cod is a long-term supply possibility as it is possible to farm the cod in a way that could reduce the risk of liver contamination through controlled feed. Furthermore, farmed cod is very different from most farmed fish in that a low 14 percent protein diet is preferred, thus limiting or eliminating the need for soy meal. Currently, limited cod fish farming takes place in the north Atlantic—my guess is that today less than 5 percent of the livers used for cod liver oil are from farmed cod—but fresh water cod could also be farmed in lakes and ponds throughout the world.

Most of the food for the cod is fish meal and oil and if the fish farm has incentives, careful selection of clean food can and is being used. The end result could be a cod that has limited exposure to most contaminants and an increase in the availability of good clean cod and cod livers.

The reason cod fish farms use a low-protein diet is because a high-protein diet produces cod with very large livers. The livers are a by-product and the fish farmer’s efforts are focussed on growing the meat. A cod’s liver typically is 10-13 percent percent of the total fish weight. The liver oil is about 50 percent of the weight of the liver. One cod weighing 5 kilograms (about 11 pounds) renders about 8 ounces of cod liver oil.

Cod fish farming may become more and more necessary because of increasing pressure to limit the number of cod caught. Much of this pressure is coming from the European Union and environmental activist organizations such as Green Peace. These groups view farmed cod as an environmentally friendly way to satisfy the growing demand for cod liver oil.
TRADITIONAL COD LIVER OIL PREPARATION

A description of traditional cod liver oil processing is provided by F. Peckel Möller in an article entitled “Cod-Liver Oil and Chemistry,” published in London, 1895. “The primitive method. . . is as follows. As soon as the fishermen reach the Voer [pier], and 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 stow away 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 that they have filled. The first of these, it may be noted, date from January, and the last from the beginning of April, and as on their arrival at their homes the fishermen 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 state 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 colour, 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 colour: this is drawn off, and the livers are left to undergo further putrefacton. 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 colour, 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. . . . In order to fully carry out the extraction, it is necessary to raise the temperature considerably above the boiling point of water. . . . 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 colour, and it is therefore termed brown oil. . . “

The writer then describes processing methods introduced to Norway in the 1850s by Peter Möller, which resulted in a much purer, consistently light-colored oil made from fresh, not putrefied livers, considerably more palatable in terms of taste and smell. He notes, however, that the “brown oils are actually used to a certain extent for medicinal purposes at the present day.” Perhaps the dark brown oils contained, in addition to vitamins A and D, vitamin B12 and other nutrients from the hepatic tissues.