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Recipe for Black Salt

Burning seaweed to make ‘black salt’ for human consumption and cattle licks has been historically recorded along the fringes of the damp North Atlantic region. The practice of producing black salt was recorded in twelfth century Denmark  and in the medieval Norwegian Gulaþing law, traces have further been found in Viking Long boats excavated in Iceland and Japanese moshio salt has been produced from at least the first millennium, by burning seaweed and mixing the ashes with seawater.

Investigating salt production in Early Medieval Ireland, Nikolah Gilligan proposes that salt could have been produced from seaweed - by drying it, burning it, soaking the ashes in water, removing the charcoal and boiling or allowing the water to evaporate until salt crystals form. The recipe below presents her step by step guide to producing black salt from the filtered ashes of burnt seaweed.

For detailed information on the experiment and a history of salt in Early Medieval Ireland read Nikolah's article Salt from Seaweed? An Experimental Archaeology.

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3 large sacks of seaweed collected from seashore. (Any type common to Irish or British coasts, eg fucus)


  • Gather three large sacks of seaweed from the seashore. 
  • Hang up to dry inside for a week or so. Dig a pit roughly measuring c. 1m wide, c. 1m long and 0.40m deep.
  • Gather firewood, build a fire in the pit. Add seaweed into an enclosed area in the middle of the fire.
  • Allow the seaweed to turn to ash over a few hours.
  • Allow the seaweed ashes to cool slightly.
  • Scoop the seaweed ashes into metal buckets to cool overnight.
  • Pour water into the buckets and allow it to soak through. 
  • Pour the water and ash mix through filtered paper (coffee filters will work) into a clean bucket or jar. Do this as many times as you want!
  • Boil the clean water or allow it to evaporate naturally. The quicker the water evaporates the smaller the granules which are formed.
  • Voilà - salt made seaweed!
Nikolah Gilligan

Nikolah Gilligan is a self-employed archaeologist and archaeobotanist. She is currently on leave from her PhD in UCD School of Archaeology, which is focused on research into early medieval food production, processing and consumption.