The method of obtaining
Grey salt and fleur de sel are hand-harvested sea salts that come exclusively from salt marshes. They are unrefined and unwashed products after harvesting. They are formed by crystallisation and consist mainly of sodium chloride crystals, but also naturally contain other mineral salts and trace elements.
The production of grey salt and fleur de sel is based on a natural process of salt concentration by evaporation of sea water to the point of crystallisation. This production is carried out in salt marshes. This age-old technique uses the ability of chlorides to crystallise under the action of evaporation by the sun and wind. Thus, salt crystals are only formed during the summer months under favourable climatic conditions. For the rest of the year, the producer (known as a salt worker or saunier, depending on the region) maintains the salt pans in a state of production for the following summer.
The salt marshes consist of a succession of man-made basins built on naturally impermeable clay soils in which water from the Atlantic Ocean, brought in by canals, flows by gravity at a rate and flow controlled by the producers. There are various sea salt production sites in France. Depending on the climatic conditions to which the salt ponds are subjected, the structures of the salt works differ slightly and the number of ponds varies.
Seawater flows into the saltworks directly from the traicts or the prouds or through the étiers or the channels. The estuaries or channels are canals that serve both to distribute the sea water and to evacuate the fresh water present in the saltworks whenever necessary. At this stage of the process, the salt concentration of the seawater is between 20 and 30 g/l.
The water is then distributed to a series of basins, all of which will contribute, through physical processes, to the evaporation of the sea water, leading to a sufficiently high concentration of salt to cause crystallisation (when the salt concentration of the water reaches 250 g/l).
The name of these basins varies according to the production area. In Guérande, these basins are the following in the order of water circulation: the vasière, the cobier (optional), the fares, the adernes and finally the œillets (crystallisation tanks).
The circulation of water in the different basins allows for a better concentration of salt, a purification of the water and a decantation of the suspended matter before arriving in the harvesting basins, the oeillets.