Q: There are so many varieties of salts available. Which should I use?
I assume that you are referring to Sodium Chloride (NaCl), the stuff found in common table salt. As well as table salt, varieties include kosher salt, sea salt, and salts of various colors. The question of which to use is not simple to answer.
When salt is used in recipes where it is dissolved amid a number of other strong flavors, most people can’t taste any real difference, but I always recommend trying for things yourself.
Make a soup from scratch, once using regular table salt and again using sea salt or kosher salt. Taste them. If you can honestly tell one from the other, you should use the salt that tastes better to you, whichever that is. If not, use table salt, which can be one sixtieth or less of the cost of the fancier salts.
Expensive salts are better used where their texture and subtle flavors can be enjoyed – at the table or for garnishing. Cook's Illustrated (October 2002) agrees, saying, “Don’t waste $36-a-pound sea salt by sprinkling it into a simmering stew.”
If you are going to substitute one kind of salt for another, coarser grained salts contain less per unit volume, because of the structure of, and the spacing between, crystals. Table salt may take as little as half the amount of coarse salts for the same taste. Use less of finer grained salts, where possible, and adjust later.
Always use table, or other fine-grained salt, in baking where it distributes more evenly with the other dry ingredients. The exception, of course, is where salt is used as part of the appearance and finish, such as the coarse salt sprinkled on pretzels. For breads and batters, some cooks prefer a flaky sea salt, because they believe it dissolves easier. Because additives can cause cloudiness in pickles, it is best to use only pickling salt for that purpose. Also, remember that the iodine added to table salt is an essential nutrient, which prevents goiter, a swelling of the thyroid gland, in those areas where not enough iodine can be found in the rest of the diet.
Finally, in his book What Einstein Told His Cook: Kitchen Science Explained, Robert Wolke suggests that some salts marketed as being sea salts may actually be mined from the same caverns as ordinary table salt. All salt originally came from the seas. Some of it has just been around for a few million years in underground caverns. Caveat Emptor, indeed.