Kosher salt is a special type of salt which is not heavily refined, allowing it to retain a flaky, multifaceted crystalline structure. Regular table salt, on the other hand, is milled so that it has a uniform crystal structure. Under a microscope, table salt takes the form of regularly shaped cubes, while kosher salt looks like a series of randomly attached crystals. These structural differences cause these salts to perform differently in cooking, which is why recipes may call specifically for one or the other.

Kosher salt is thus named because it has traditionally been used in kosher butchering. You may sometimes see it labeled as “koshering salt” for this reason, since it is used as part of the koshering process which makes meat safe to eat for Jewish people who observe dietary guidelines. In addition to being only lightly refined, kosher salt also have no additives such as iodine, making it a very pure, plain salt with a mild flavor.

The many faces of a single grain of kosher salt make it ideal for things like curing meats and vegetables, since the faces can help the salt absorb more moisture. Kosher salt is also used for things like making ice cream and even salting roads in the winter; in this case, it may also be known as “rock salt.” If you're wondering how salt is involved in the ice cream making process, kosher salt is added to the ice crystals packed around the container in an ice cream maker to lower their freezing point, thus making the ice cream even colder.

The large grains of kosher salt make it unsuitable for some cooking applications. It is not generally used as a table salt, for example, since the grains are too large to dissolve when they are sprinkled onto food. Kosher salt is also not the best choice for baking, since the grains will clump in baked goods, rather than separating out and melting into the recipe, as is desired. This salt can be used for a crunchy texture to top focaccia or to make a crust for roasted fish, often with a very dramatic effect.

Plain table salt comes in a range of styles as well, in addition to the standard fine grained variety. Fleur de sel, for example, is a fine, flaky type of sea salt from France which tastes more natural than refined, iodized salt. For sprinkling on already cooked foods and baking, table salt is preferable, but you may want to explore the wide variety of gourmet and specialty salts at your disposal.