Please tell me about sea salt. Why are so many chefs and recipes using it these days?

Boy, am I glad you asked that question! I've been waiting for a good excuse to vent my spleen on that subject. Stand back.

There is so much nonsense out there about sea salt that it's hard to know where to begin. It's easy to dismiss the assertions of some health-food faddists, who often require no evidence whatsoever before adopting a fervent conviction. Among the statements I've seen are that sea salt is "unrefined," "organic," "more natural," "more healthful" and "a living food," whatever that means. (Does it bite back?)

Poppycock, all. 'Nuff said.

Moving from the ridiculous to the sublime, it's not quite as easy to dismiss the pronouncements of respected chefs and cookbook authors, whose statements tend to be accepted as gospel even when misguided. Their misguided statements tend to cluster around two supposed virtues of sea salt: its high mineral content (a claim made even more passionately by health-food addicts) and its superior flavor. I'll address the mineral question in this column and the flavor issue in my next one.

Those magnificent minerals

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--salt. Ninety-nine percent of the rest consists of magnesium and calcium compounds. 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 stuff, are present in nutritionally negligible quantities. You'd have to eat two tablespoons of it to get the amount of iron, for example, in a single grape.

Bowl of salt sludge, anyone? Not in the United States, because although people in coastal regions of some countries do use this raw material as a condiment, the Food and Drug Administration requires that food-grade salt be at least 97.5 percent pure sodium chloride.

But that's only the beginning of the Great Mineral Hoax. Because of how food-grade sea salt is extracted, the stuff that winds up in the stores contains about 10 times less mineral matter than the raw salt sludge. Food-grade sea salt is obtained by allowing the sun to evaporate much of the water, but by no means all of it--and that's a critical distinction--from shallow ponds of seawater. When the concentration of sodium chloride in the ponds gets to be about nine times what it was in the ocean, it begins to crystallize out, whereupon it is raked or scooped out for subsequent washing, drying and packaging.

The vital point that nobody seems to realize--or admit--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.

Here's why.

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. The crystallized salt (called solar salt) that is harvested by solar evaporation of ocean water is therefore about 99 percent pure sodium chloride right off the bat. The other 1 percent consists almost entirely of magnesium and calcium compounds. Virtually all of those other 75-or-so "precious mineral nutrients" are gone. To get that single grape's worth of iron, you'd have to eat about a quarter of a pound of solar salt!

Even beyond that, some brands of sea salt are the result of subjecting the solar salt to the same further purification steps as mined salt, reducing their mineral content effectively to zero.

Is "sea salt" sea salt?

Let's not forget that mined salt is also sea salt, because the underground salt deposits were left by ancient seas that dried up. It therefore has a very similar composition--minerals and all--to today's sea salt. And how about this little-known fact: Your "sea salt" might not even have been taken from the sea, because 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 be 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 million years earlier.

Many sea salt enthusiasts deceive themselves by thinking that there are only two kinds of salt: mined salt in the shaker and sea salt in the fancy packages. Not only may the "sea salt" have come from a mine, but on the West Coast the salt in the shaker is most likely to have come from the sea. The point is that a salt's characteristics depend much more on how the raw material has been processed than on where it came from. You can't just generalize. There are probably a dozen brands of genuine sea salt with crystals of a variety of sizes, shapes and degrees of purity. Some are straight solar salt, while some have been purified further.

The bottom line is that when a recipe specifies simply "sea salt" it is pure folly, and stems from a lack of knowledge, misguided political correctness or a thoughtless desire to climb onto a popular bandwagon. And you know what? It may make absolutely no difference anyway.

That was a teaser for my next column, in which I'll examine a few flavor fables. Do sea salts really make food taste better than mined salts? And if so, which ones are best?

Don't go too far away.

Labelingo: Deborah M. Styles of Alexandria notes that Breyer's "Ice Cream Parlor" ice cream comes in a "New Space Saver Size!" It's 1.75 quarts instead of the usual half-gallon (2 quarts). Hey, Breyer's, I know how I can save even more space in my freezer: by buying zero quarts of your ice cream.

(Have you noticed any silly things on food labels? Send your Labelingo contributions, along with your name and town, to Food 101, Food Section, The Washington Post, 1150 15th Street NW, Washington, D.C. 20071 or to the e-mail address below.)

Robert L. Wolke is professor emeritus of chemistry at the University of Pittsburgh. His latest book is "What Einstein Told His Barber: More Scientific Answers to Everyday Questions" (Dell Publications, $11.95). Send your kitchen questions to wolke@pitt.edu.