Where Does Salt Come From? Ask Paul

All salt starts out either in the ocean or in underground deposits (which were also oceans, millions of years ago). But how it is retrieved from the land or sea, and what exactly happens to it afterward, makes a vast difference to the form and flavor of the crystals. Here are some of the paths salt can take to get to your table.

The Sea

Seawater is about 3½ percent salt by weight. To harvest the salt, water must be removed, either through solar evaporation or by heating in vast pans. 

In warmer climates with low rainfall, seawater is channeled into enormous shallow pools or ponds and allowed to slowly evaporate in the heat of the sun.

As the water evaporates, the solution of salt water in the pool becomes more concentrated, and salt crystals start to form.

In regions where the climate doesn’t have enough dry, sunny days to evaporate open-air ponds, salt makers heat giant pans of seawater to achieve a similar result. 

Underground Deposits

Salt that’s found in underground deposits must be mined, like any other mineral. This is done in one of two ways: either by excavation or a process known as “solution mining.”

Excavating requires blasting, boring, and manual labor to harvest solid salt from the earth. The salt is extracted in large pieces; if it’s destined for culinary purposes, it must be crushed and sifted.

With solution mining, the underground salt is essentially turned back into seawater: Water gets pumped into the mine, where it dissolves the salt it comes in contact with. The resulting strong brine is pumped back out, and evaporation is used to remove the water and leave the salt. 

In their minimally processed forms, these salts that come out of the earth or sea can retain trace minerals, as well as particles of algae and bacteria. If they’re used with these impurities intact, the salts retain a unique character that makes them attractive as finishing salts, where their interesting flavor, color, and texture will stand out.

Maldon sea salt is one of these. It's produced in the seaside town of Maldon, England, from seawater that is evaporated in heated pans. (The British climate is not good for outdoor solar evaporation). During slow, controlled evaporation, salt crystals take the shape of inverted, hollow four-sided pyramids, which float on the brine like tiny boats. These pyramid-shaped crystals crush easily between the fingers for sprinkling and also dissolve quickly on the tongue.

Fleur de sel is a sea salt produced in Brittany (and similar salts are produced elsewhere). During solar evaporation of seawater, the first crystals to form float on the surface of the brine. Saltmakers can skim these off as they form; their flaky texture and clean flavor makes them prized among salt lovers.

The French solar saltmakers also produce sel gris, which consists of crystals scooped from the bottom of the evaporation pool. This salt gets a gray color from minerals (such as calcium and magnesium) it contacts at the bottom of the pool. These minerals also cause it to retain water, so sel gris is still moist when it’s sold.

In the Salt Range mountains of Pakistan, a centuries-old network of mines excavates large rosy pieces of Himalayan salt, which gets its color from trace amounts of included iron. This salt is ground into grains of various sizes for culinary use, but also, as the salt’s fame has grown, hunks and slabs are often sold for use as plates, lamps, and bricks.

Other mined salts often have striking colors from mineral inclusions. Redmond salt is another pinkish variety, mined in Utah. Persian blue salt is mined in the north of Iran and gets its startling azure color from ancient damage done to the molecular crystalline structure of the salt due to its proximity to underground potassium deposits.

The overwhelming majority of salt, from both mines and seas, undergoes refining steps before it is sold. 

To make refined products such as table and kosher salts, producers purify salt by stripping away its tasty minerals and other impurities that dilute sodium chloride (NaCl) until the salt contains around 97 percent pure NaCl.  

The refining process starts with dissolving the salt—whether it originally came from deposits, such as Diamond Crystal’s Michigan mines, or the sea, such as Morton’s salt pan operation in the Bahamas—into a brine. Then, the salt undergoes repeated evaporation steps, causing unwanted minerals to settle out in order to isolate the NaCl.

The uniform, cube-like structure of table salt grains forms naturally when the salt crystallizes. To standardize the size of the grains, producers sieve out larger crystals.

But depending on factors including the speed and method of evaporation, salt crystals can be induced to grow in a variety of shapes: flat flakes, dense chunks, and irregular agglomerations. Some kosher salt, such as Morton’s, is made by pressing salt cubes between hot rollers to flatten them into flakes. Diamond Crystal kosher salt, on the other hand, is formed by evaporation under vacuum at cool temperatures, which helps produce hollow pyramid-shaped crystals, smaller than those found in Maldon salt.