Due to a lack of sunshine, the bay of Mont-Saint-Michel has never had salt marshes. But from the Middle Ages until 1865, so-called igniferous salt was produced. Obtained by evaporation using fire, this salt was not made from sea water but from sand. The salt farmer would plough the sand from the beaches before piling it up. The sand was then washed over a ditch, over a straw filter, so as to dissolve the salt, which flowed into a barrel. The brine was then cooked for about three hours. Although the yield was low and the process consumed a lot of wood, it produced a very white and fine salt without impurities.