Moshio salt (藻塩) is a type of Japanese sea salt made using an ancient method where it is collected using a dried seaweed known as hondawara (Sargassum fulvellum). The seaweed is believed to confer additional umami flavor to the salt.^[1][2]

Japan's climate is too cool and wet to allow easy production of salt by simple evaporation of sea water.^[1] Boiling down sea water directly used a tremendous amount of fuel, so seaweed was historically the main technique used until the 7th century when enden pan salt – clay pan salt fields – became the main salt production technique.^[2]

Process

To make the salt, the seaweed is dried out, and salt crystals form on the seaweed. These are collected by boiling the seaweed in seawater in bags to form a concentrated brine. The resultant solution is boiled down until it crystallizes out.^[1][2]