High and dry: cold air preserved cod in Viking times Olaf Kruger/imageBROKER/REX/Shutterstock

Norwegian cod may have arrived in Germany hundreds of years earlier than we originally thought, thanks to the ingenuity of the Vikings. It seems they worked out 1200 years ago how to freeze-dry fish to keep it fresh on the long voyage from the Arctic.

Bastiaan Star of the University of Oslo, Norway, and his colleagues analysed DNA from 15 samples of ancient cod at five locations across north-west Europe – the southernmost samples coming from Haithabu, a Viking-age village in what is now northern Germany.

By comparing the ancient DNA with genetic material taken from around 170 modern cod tissues, Star and his colleagues confirmed that four cod samples from Haithabu originated in the north-east Arctic, close to the northernmost tip of the Norwegian coast.


The only explanation is that Viking ships transported the cod – a sea journey of 2000 kilometres that would have taken at least a month. Even then, Vikings – renowned for their maritime prowess – had developed a geographically extensive trade in fish, a perishable resource.

Winter catch

The other key implication of the discovery is that the Vikings had worked out how to freeze-dry fish. Arctic cod populations only come close to the Norwegian shore to spawn in winter, and in Viking times that would have made them easier to catch. The winter chill would have made it simple to freeze-dry the fish naturally. The Vikings might have hung the fish from wooden racks in the open air so the clean, sea winds and freezing temperatures would do the rest.

“Dried cod, properly treated, can last for more than five years,” says Star.

The new study suggests that, centuries earlier than the first documented use of salt to preserve Norwegian fish in the 1690s, Vikings already knew how to keep cod fresh enough to sell in distant markets.

“The early trade of dried cod, if this is what the bones represent, suggests the emergence of exchange in bulk commodities, not just prestige goods,” says James Barrett of the University of Cambridge, who collaborated with Star on the study. “This is a potentially transformative development in the relationship between human groups, and between humans and the natural resources they extract.”

The work “adds to the richness of our understanding of the Viking sphere of influence”, says Jeremy Searle of Cornell University in Ithaca, New York, who previously showed how Norwegian mice spread widely by stowing aboard Viking ships.

Earlier on researchers in the UK identified cod vertebrae from the early 11th century in York, which was once a Viking city. “We’ve always thought the fish was air-dried to preserve it on the long journey from Norway,” says Sarah Maltby of the York Archaeological Trust. “There seems no end to Viking ingenuity in this period.”

Journal reference:

Journal reference: PNAS, DOI: 10.1073/pnas.1710186114