Salted_ A Manifesto on the World's Most Essential Mineral, With Recipes - Mark Bitterman [29]
The brine then passes to the adernes, the final evaporating basins before crystallization. The adernes often comprise the largest surface area of the evaporating basins after the fares, each measuring about 50 by 80 feet. More calcium salts may crystallize here. The adernes are very shallow, allowing the water to heat and evaporate rapidly. Here, water can reach 86 to 95°F, and salinity will reach 25 percent.
When the brine is virtually saturated with salt, it is passed into the most meticulously crafted basins of all, the oeillets, or crystallizing pans. The pale porcelain argile clay from which the salt pans are formed provides a perfect, effectively hermetic environment for the production of salt. In addition to being highly malleable, the clay has good refractory properties, maximizing the amount of heat captured from the sun.
The oeillets vary in size depending on the salt maker’s preferences and local tradition, but are often about 30 feet square; many are rectangular, with dimensions more like 20 by 30 feet. Because one cannot wade into the pans without disturbing the delicate porcelain clay bottom, the oeillet’s dimensions are restricted by the length of the rake that can be handled to reach halfway across it. The water level in these pans is as shallow as ¼ inch and salinity reaches 30 percent. Here, finally, salt crystals form. Sel gris and traditional salt will form throughout the salt-making season. On the Atlantic coast, fleur de sel only comes on warm, sunny days, when a light wind ruffles the water. When it does appear, each oeillet will produce 4.5 to 6.6 pounds of fleur de sel in a day, compared to 90 to 165 pounds of sel gris.
The wind plays a vital role in crystallization by increasing the amount of water vapor that can be carried away from the surface of the water. Lack of wind can be just as serious a problem in a salt field as rain. The Trapani salt fields of Sicily have been known to suffer radical drops in salt production due to occasional calms that descend on western Sicily in the summer.
The Camargue on the Mediterranean coast of France is one of Europe’s most productive salt-producing regions. In addition to long, dry summers, the region is buffeted by two different winds: the moist tramontane descending from the Pyrenees and the drier mistral emanating from the Alps to the northeast. The combination of strong sun and multiple winds (not to mention mechanization) helps make the solar salt fields of the Camargue the most productive in Europe.
A major difference between industrial salt makers and most artisans is the salinity level at which the brine is admitted to the crystallizers, and its finished salinity when it is evacuated. Different minerals will crystallize from brine at different levels of salinity based on their solubility in water. Some minerals, like calcium, are far less soluble than sodium, and so they crystallize and precipitate out of the brine earlier. Others, like magnesium and potassium, are more soluble, so they crystallize later. Artisans may admit water into crystallizers at 15 to 17° Baumé (a measure of the density of the water, and hence of its salt concentration), which is early enough to allow for considerable amounts of low-solubility salts and trace minerals to crystallize along with the sodium chloride. Industrial producers, keen on capturing pure NaCl, wait until 24° Baumé. Artisan salt makers may also wait longer to evacuate the dense brine left over after most of the sodium chloride crystallization has occurred, allowing more of the magnesium