Cod-liver oil

Cod liver oil is a nutritional supplement derived from liver of cod fish (Gadidae). As with most fish oils, it has high levels of the omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Cod liver oil also contains vitamin A and vitamin D. It has historically been taken because of its vitamin A and vitamin D content. It was once commonly given to children, because vitamin D has been shown to prevent rickets and other symptoms of vitamin D deficiency.

Cod liver oil has traditionally come in many grades. Cod liver oil for human consumption is pale and straw colored, with a mild flavor. Ancient Scandinavian Vikings produced cod liver oil by laying birch tree branches over a kettle of water, and fresh livers were laid over the branches. The water was brought to a boil and as the steam rose, the oil from the liver dripped into the water and was skimmed off. There was also a method for producing fresh raw cod liver oil.

In the Industrial Revolution, cod liver oil became popular for industrial purposes. Livers placed in barrels to rot, with the oil skimmed off over the season, was the main method for producing this oil. The resulting oil was brown and foul tasting. In the 1800s cod liver oil became popular as a medicine and both pale and brown oils were used. Brown oils were common because they were cheaper to produce. Some doctors believed in only using the fresh pale oil, while others believed the brown oil was better. However the brown oils tended to cause intestinal upset.

The Möller Process was invented by Peter Möller in 1850. The livers are ground with water into a slurry, then this is gently simmered until the oil rises to the top. The oil is skimmed off and purified.

Other methods used in modern times include the Cold Flotation Process, Pressure Extraction, and Pressure Cooking. These all require further purification steps to get a pure oil.

Fermented Cod Liver Oil is made using a trade secret process, but is thought to be similar to the method to produce brown oil in the 1700s and 1800s. Testing has shown FCLO has high levels of free fatty acids and a high acid value, indicating possible prolonged rancidity. However, free fatty acids and acid value may not be the correct marker to reflect the oxidation level of this product.

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