Sel gris (pl. sels gris, "gray salt" in French, also known as Celtic sea salt) is a coarse granular sea salt popularized by the French.
Sel gris comes from the same solar evaporation salt pans as fleur de sel but is harvested differently; it is allowed to come into contact with the bottom of the salt pan before being raked, whence its gray colour. Sel gris is coarser than fleur de sel but is also a moist salt, typically containing 13 percent residual moisture.
The bottom of the salt pan (French oeillet) may be composed of clay, basalt, sand, concrete, or even tile. This keeps the salt from coming into contact with the silt beneath and becoming dirty. Every few days or even daily, the harvester (French paludier) pushes or pulls the salt with a long wooden rake. This must be done carefully as the depth of the brine may be as little as ¼ inch and the clay bottom must not be penetrated at the risk of contaminating the salt. The salt is raked toward the sides of the pan where it is then shovelled into a pile and left to dry slightly before storing. 90 to 165 pounds of sel gris can be harvested in one day, whereas for fleurs de sel the daily yield is only 4.5 to 6.6 pounds.
Because of its mineral complexity and coarse grain size, sel gris can be used both as a cooking salt and a finishing salt. Being much denser than table salt, there is a lot more salt in an equivalent volume of sel gris.