Salt

Types of salt

For the most part, the various grades of salt are all the same; chemically most are greater than 99 percent sodium chloride, but the structure varies widely. Simple table salt consists of small, compact cubic grains, while kosher salt has a much more irregular structure and a larger surface area. Popcorn salt is ground salt that dissolves very quickly. Rock salt is just that, large chunks of sodium chloride. These differences in structure can cause a significant change in the perceived flavor of the salt and its usefulness for particular recipes. The speed with which it dissolves is also very important, with finer salts such as pickling salt even dissolving readily in cold liquid.

Sea salt, made from evaporating seawater, also varies considerably. Because there are impurities in the water, each sea salt has a unique taste and is prized in different cuisines or for different applications. Sea salts often tend to cost considerably more than other kinds of salt; however, in areas with large seawater evaporation industries (such as California) the "table salt" in local stores may actually be sea salt.  Another example is Cayman Sea Salt.

Uses

Salt has many uses in cooking beyond simple flavoring. Its chief utility lies in its osmotic properties. Salting the surface of food draws out water and anything dissolved in it. When meat is koshered, it is heavily salted to draw out any remaining blood. Kosher salt, because of its structure, is perfectly suited to this task. This technique is also applied to eggplants to remove bitter flavors and alter the texture of the plant, and also when sweating aromatic ingredients such as onion or garlic over low heat to draw out their moistures and soften them.

Salt also tends to enhance our perception of other flavors, particularly that of sweetness. This explains its use in ice cream, for example, or kettle corn. Most candy recipes have a small amount of salt which cannot be directly detected, but has a noticeable effect on the final result.

Salt's thermal properties are useful in a few applications, notably in home-made ice cream. The action of rock salt dissolving in ice water pulls heat from its environment. Ice cream makers, then, sit the salt-and-ice mixture in an insulated container, and inside that is placed a highly conductive container of the cream mixture, which freezes rapidly.

Salt can be used to "fry" food as well. Large amounts of rock salt are heated in an oven to temperature (varies, generally about 400 °F or 200 °C). After the salt gets hot, the food is placed in the salt and an additional layer of pre-heated salt is poured on top. This method is an extremely fast way to get heat into food, second only to deep frying, consequently, cooking times will be very short.

When salt is added to boiling water for pasta or potatoes, two things are happening. First, the boiling point of the water is slightly raised, though not usefully so (the temperature will rise less than .25°C). Second, the salt water is flavoring the pasta or potatoes. When you add salt, you are salting the water, you are not directly salting the food. Thus the amount of salt should vary according to the amount of water, which will always seem to be too much salt.

Lastly, salt is of course used as a flavoring. Table salt is most often used for this purpose, but its chief virtue here is the added iodine which prevents goiter. However iodine has a metallic taste. Many cooks use kosher salt or sea salt in its place. Besides the iodine the big difference is that kosher and sea salt have larger sized particles of salt. This makes it easier to measure when adding to a recipe. I think sea salt may also have added minerals that kosher salt lacks.