Chemically speaking, absolutely nothing. They’re plain old salt: sodium chloride. But physically speaking, they’re either finer-grained or coarser-grained than ordinary table salt. And that’s all.
The number of specialty salts on the wholesale market is astounding.
Cargill Salt, Inc., one of the world’s largest salt producers, makes about sixty kinds of food-grade salt for food manufacturing and consumer use, including flake, fine-flake, coarse, extra-fine, super-fine, fine-flour and at least two grades of pretzel.
Chemically, all are 99-plus percent pure sodium chloride, but they possess special physical characteristics designed for use in everything from potato chips, popcorn, and roasted nuts to cakes, breads, cheeses, crackers, margarine, peanut butter, and pickles.
For margaritas, you want coarse crystals that will stick to the lime juice on the rim of the glass. (You do wet the rim with lime juice, don’t you? Not, Heaven forbid, with water?) Finer grains of salt would just dissolve in the juice.
On the other hand, for popcorn you want exactly the opposite: fine, almost powdered particles that will nestle into the kernel crannies and stay put. Grains of ordinary salt-shaker salt don’t stick to dry foods; they bounce off like the fake boulders in an Indiana Jones avalanche.
But why pay a high price for ordinary sodium chloride with a come-hither label? Kosher salt is quite coarse enough to coat a margarita rim and works very well despite the ethnic mismatch. And for popcorn, I grind kosher salt into a powder with a mortar and pestle.
I get a particular kick out of the label on one brand of “popcorn salt” that sells for nearly $5 a pound. (Table salt sells for about 30 cents a pound).
The label forthrightly declares: “Ingredients: Salt.” Well, that’s fair enough. But then it goes on to boast that it “also enhances the flavor of French fries and corn on the cob.”