The terms sea salt and regular salt or table salt are often used as if they denote two distinctly different substances with distinctly different properties. But it’s not that simple.
Salt is indeed obtained from two different sources: underground mines and seawater. But that fact alone doesn’t make them inherently different, any more than water obtained from wells and springs are inherently different because of their sources.
Underground salt deposits were laid down by ancient seas that ultimately dried up at various times in Earth’s history, from a few million to hundreds of millions of years ago. Some of the deposits were later thrust upward by geologic forces and are quite near the surface in the form of “domes.” Other salt deposits lie hundreds of feet below ground, creating a bigger challenge to mining.
Rock salt is chopped out by huge machines within caverns carved into the salt. But rock salt isn’t suitable for food use because the ancient seas trapped mud and debris when they dried up. Instead, food-grade salt is mined by pumping water down a shaft to dissolve salt, pumping the salt water (brine) up to the surface, settling out the impurities, and vacuum-evaporating the clear brine. That creates the familiar, tiny crystals of table salt in your salt shaker.
In sunny coastal regions, salt can be obtained by allowing sunshine and wind to evaporate the water from shallow ponds or “pans” of contemporary seawater. There are many kinds of sea salt, harvested from waters around the world and refined to various degrees.
There are gray and pinkish-gray sea salts from Korea and France, and black sea salt from India, all of which owe their colors to local clays and algae in the evaporation ponds, not to the salt (sodium chloride) that they contain.
Black and red sea salts from Hawaii owe their colors to deliberately added powdered black lava and red baked clay. These rare and exotic boutique salts are used by adventurous chefs. They have undeniably unique flavors, of course; they taste like salt mixed with various clays and algae. Each one has its fervent partisans.
In what follows, I am not writing about these rare, expensive ($33 or more per pound) multicolored boutique salts, which are not easily available to the home cook. I am writing about the wide variety of relatively white salts obtained by one means or another from seawater, and which for that fact alone are revered because they are believed to be rich in minerals and universally superior in flavor.
If you evaporate all the water from a bucket of ocean (fish previously removed), you will be left with a sticky, gray, bitter-tasting sludge that is about 78 percent sodium chloride: common salt. Ninety-nine percent of the other 22 percent consists of magnesium and calcium compounds, which are mostly responsible for the bitterness. Beyond that, there are at least 75 other elements in very small amounts.
That last fact is the basis for the ubiquitous claim that sea salt is “loaded with nutritious minerals.”
But cold, hard chemical analysis tells the tale: The minerals, even in this raw, unprocessed sludge, are present in nutritionally negligible amounts. You’d have to eat two tablespoons of it to get the amount of iron, for example, contained in a single grape. Although people in the coastal regions of some countries do use this raw material as a condiment, the FDA requires that in the U.S. food-grade salt be at least 97.5 percent pure sodium chloride. In practice, it is invariably much purer.
That’s only the beginning of the Great Mineral Deception. The sea salt that winds up in the stores contains only about one-tenth of the mineral matter in raw sea sludge. The reason for that is that in the production of food-grade sea salt, the sun is allowed to evaporate much of the water in the ponds, but by no means all of it, and that’s a critical distinction.
As water evaporates, the remaining water becomes more and more concentrated in sodium chloride. When the concentration of salt in the ponds gets to be about nine times what it was in the ocean, it begins to separate out as crystals, because there isn’t enough water left to hold the salt in its dissolved form. The crystals are then raked or scooped out for subsequent washing, drying and packaging. (How do you wash salt without dissolving it away? You wash it with a solution that is already holding as much salt as possible and cannot dissolve any more. In Techspeak, a saturated solution.)
The vital point here is that this “natural” crystallization process is in itself an extremely effective refining step. Sun-induced evaporation and crystallization make the sodium chloride about 10 times purer, freer of other minerals, than it was in the ocean.
Whenever you have a water solution containing a preponderance of one chemical (in this case, sodium chloride) along with a lot of other chemicals in much lesser amounts (in this case, the other minerals), then as the water evaporates away, the preponderant chemical will crystallize out in a relatively pure form, leaving all the others behind. It’s a purification process that chemists use all the time. Madame Curie used it repeatedly to isolate pure radium from uranium ore.
Salt harvested by the solar evaporation of ocean water, known as solar salt, is therefore about 99 percent pure sodium chloride right off the bat, with no further processing. The other 1 percent consists almost entirely of magnesium and calcium compounds. Those other 75-or-so “precious mineral nutrients” are virtually gone. To get that single grape’s worth of iron, you’d have to eat about a quarter of a pound of solar salt. (Two pounds of salt can be fatal.)
Incidentally, the notion that sea salt arrives naturally iodized is a myth. Just because certain seaweeds are rich in iodine, some people think of the oceans as vast pots of iodine soup. In terms of the chemical elements in seawater, there is 100 times more boron, for example, than there is iodine, and I’ve never heard anybody tout sea salt as a source of boron. Un-iodized commercial sea salts contain less than 2 percent of the amount of iodine in iodized salt.
Is “sea salt” sea salt?
Actually, the “sea salt” sold in markets might not even have been taken from the sea, because as long as they satisfy the FDA’s purity requirements manufacturers don’t have to specify their sources, and according to industry insiders I have talked with, fibbing does occur.
Two batches of salt may have been taken from the same bin at the mine plant and one of them labeled for sale as “sea salt.” Well, of course it is. It just crystallized a few million years earlier. Conversely, on the West Coast of the U. S. the common table salt in the salt shaker is most likely to have come from the sea, rather than from a mine.
The point is that a salt’s characteristics depend on how the raw material has been processed, rather than on where it came from. You can’t generalize. Thus, when a recipe specifies simply “sea salt,” it is a meaningless specification. It might as well be specifying “meat.”
Sea salt is often specified to avoid the “harsh-flavored additives” in shaker salt.
Whether from a mine or a sea, shaker salt does indeed contain anti-caking additives to keep its grains flowing smoothly, because they are tiny cubes and their flat surfaces tend to stick together. But the FDA limits the total amount of all additives to a maximum of 2 percent, and it is invariably much less than that.
Morton’s table salt, for example, is more than 99.1 percent pure sodium chloride and contains only 0.2 to 0.7 percent of the anti-caking agent calcium silicate. Because calcium silicate (and all the other anticaking agents) are insoluble in water, shaker salt makes a slightly cloudy solution.
Other common anti-caking additives are magnesium carbonate, calcium carbonate, calcium phosphates, and sodium aluminum silicates. These are all completely tasteless and odorless chemicals.
But even if they weren’t, even if expert tasters could detect subtle flavor differences among solid salts due to an additive of less than one percent, the 50,000-fold dilution factor that occurs when the salt is used in a recipe would certainly wipe them out. Just do the math. One percent of a 6-gram teaspoon of salt is 0.06 gram of additive in 3 quarts or more than 3,000 grams of stew: 3,000 ÷ 0.06 = 50,000.
There is no denying that some of the finer (read more expensive) sea salts, even below the boutique level, have interesting flavor characteristics. But that depends on how they are used and on what your definition of “flavor” is.
A food’s flavor consists of three components: taste, smell, and texture. With salt, we can pretty much eliminate smell because neither sodium chloride nor the calcium and magnesium sulfates that may be present in some of the less purified sea salts have any odor. (Techspeak: They have exceedingly low vapor pressures.) Nevertheless, our sense of smell is very sensitive, and it is possible that a smell of algae in these less purified salts might be detected. Also, when any kind of salt is inhaled nasally as a fine dust, some people report a slight metallic sensation high in the nose.
That leaves taste and texture: what the taste buds actually detect and how the salt feels in the mouth.
Depending on how they were harvested and processed, the crystals of different brands of sea salt can vary widely in shape, from flakes to pyramids to clusters of irregular, jagged fragments. (Check them out with a magnifying glass.) The sizes of the crystals also can range from fine to coarse, although virtually all of them are coarser than shaker salt.
When sprinkled on a relatively dry food such as a slice of tomato just before serving, the bigger, flakier crystals can deliver bright little explosions of saltiness as they hit the tongue and dissolve or as they are crushed between the teeth. That’s why the savviest chefs value them: for those sensuous little bursts of saltiness. Shaker salt doesn’t do that because its compact little cubes dissolve on the tongue much more slowly. Thus, it is the complex shapes of the crystals, not their nautical origin, that give many sea salts their sensory properties.
The reason that most sea salts have large, irregularly shaped crystals is that that’s what slow evaporation produces, whereas the rapid vacuum-evaporation process used in making shaker salt produces tiny, regularly shaped grains designed to fit through the holes in the shaker. That’s a phenomenon well known to chemists; the more rapidly crystals grow, the smaller they will be.
Crystal size and shape are irrelevant when a salt is used in cooking, because the crystals dissolve and disappear completely in the food juices. And once dissolved, all textural differences are gone.
The food doesn’t know what shape the crystals were in before they dissolved. That’s another reason why it’s silly to specify sea salt in any recipe that contains moisture, and what recipe doesn’t? Using it to salt the water in which vegetables or pasta are to be cooked makes even less sense.
But are sea salts perhaps still distinguishable from one another in flavor, even though dissolved in water? In a series of controlled taste tests reportedly conducted in 2001 under the auspices of the Leatherhead Food Research Association in England, panels of tasters attempted to distinguish among a number of different salts dissolved in water. The results, as reported in Vogue magazine, were wholly inconclusive.
One common assertion is that sea salt is saltier than shaker salt. But since they’re both about 99 percent pure sodium chloride, that can’t be true. The idea undoubtedly arose from the fact that in onthe-tongue taste tests, the flaky, irregularly shaped crystals of many sea salts dissolve instantly, giving a quicker rush of saltiness than do the small, compact, slow-dissolving little cubes of shaker salt. But again, it’s not the ocean that made that difference; it’s the shapes of the crystals.
The notion that sea salt is saltier has led to the claim that one can use less of it in seasoning. (“Good for those watching their sodium intake,” trumpets one sea salt manufacturer.)
Obviously, because sea salts generally have big, complexly shaped crystals that don’t pack down as tightly, a teaspoonful will contain less actual sodium chloride than a teaspoonful of tiny, compact shaker grains. Teaspoon for teaspoon, therefore, sea salt is actually less salty than shaker salt. Weight for weight, of course, they’re identical, because any gram of sodium chloride is precisely as salty as any other. You can’t cut down on salt by eating the same weight of salt in a different form.
Making the most of it
At home in your kitchen, which coarse, complexly grained sea salt should you sprinkle on your foie gras or venison carpaccio just before serving? The ones that earn the most frequent praise from chefs are the (surprise!) French salts harvested from the coastal waters of southern Brittany at Guérande or on the île de Noirmoutier or île de Ré. You will find them in several forms. Gros sel (big salt) and sel gris (gray salt) are the heavy crystals that fall to the bottom of the salt ponds and may therefore be gray with clay or algae.
In the battle of the sea salts, most connoisseurs agree that the champion is fleur de sel (flower of salt), the delicate crust of crystals that forms on the surface of the French ponds when the sun and wind are exactly right. Because it forms in very limited amounts and must be carefully hand-skimmed from the surface, fleur de sel commands the highest price and is (as a consequence, perhaps?) most highly regarded by leading chefs.
Because of its fragile, pyramidal crystal shape, it does indeed produce a delightfully crunchy salt-burst when sprinkled on relatively dry foods just before serving or at the table.
But cooking with it is pointless.