“Celtic” sea salt, most commonly known as Sel gris or gray salt in French is harvested from seawater in the estuaries near the town of Guérande in France. As the tide comes in, seawater is first allowed to settle in clay silt ponds where the combined effects of wind and sun form a dense brine. The brine is then channeled to shallow salt pans dug in the native clay where it crystallizes via solar evaporation to form salt. The clay from the silt as well as from the salt pans impart Sel gris with its characteristic gray color. Sel gris is a coarse salt that is typically harvested with a moisture content of 15%, whereas most sea salts and commercially manufactured salt maintain moisture contents of less than 1%.
I know of no comprehensive, modern analysis of Sel gris, so it is difficult to determine if the harvesting of sea salt from the estuaries near Guérande affects the salt concentrations normally found in seawater. From a chemical perspective, there is no reason to expect that the relative concentrations of the dissolved elements normally found in sea water would be altered, unless the processing of Sel gris adds or subtracts elements. The salts in seawater are stable chemical compounds whose relative percentages are invariant.1, 2 The absolute weights of each of seawater’s dissolved salts will vary depending only upon the amount of moisture that is retained in Sel gris at harvest. Because Sel gris is typically harvested with a 15% moisture content, then the absolute weight of the dissolved salts will be about 85% of their equivalent amount in dry sea salt (<1 % moisture).
In the single account3 I am aware of, the following concentrations of dissolved salts were reported for Sel gris (100 grams):
- Sodium 34 grams
- Calcium 287 mg
- Potassium 109 mg
- Magnesium 34 mg
- Iron 11 mg,
- Manganese 1 mg
- Zinc 0.35 mg
Let’s take a look at these values and contrast them to normal dry (no moisture) sea salt or normal sea salt containing 15% moisture which is similar to Sel gris’ moisture content in the table below.
