Salt production is one of the oldest chemical practices performed by man. Salt is produced naturally when sea water evaporates, but the process can easily be reproduced to create a higher yield. Although some salt is still produced using ancient methods, new, faster, and less expensive methods have been developed. Depending on the source of the salt and the method used to create it, the end product will have a differing flavors and textures.
Today there are two main methods for obtaining salt, evaporation from sea water and mining salt from the earth. Most common table salts and salts used for industrial purposes are obtained through mining, while specialty or gourmet salts are still produced via evaporation of sea water.
Salt accounts for about 3.5% of the world's oceans and is naturally produced when shallow ponds and bays dry up in the sun and wind. Large salt crystals are left behind where the the salty water once was. When producing sea salt on an industrial scale, sea water is placed in large "concentrating ponds" to allow efficient evaporation from the sun and wind. Manufacturing of sea salt can only be performed in areas with low rainfall in order for enough time to pass for evaporation. For this reason, salt is often produced in dry climates such as the Mediterranean and Australia.
Sea salt is also produced on a much smaller scale and by ancient, skilled methods. Fleur de sel is an example of such an artisan salt that is still, to this day, produced by ancient methods. This light, flakey salt is produced in small ponds in France and is only made during the summer months of May to September.
Salt is present in the rocky under layers of the Earth's surface and can be extracted through mining. These large deposits of salt are the result of ancient underground waterways that have long since dried up.
Rock salt is extracted through dynamite, similar in fashion to the mining of any other mineral. Once it is brought to the Earth's surface, it is crushed and used for industrial and other non-food purposes. This type of salt contains many minerals and other impurities.
Hydraulic mining of salt involves pumping water below the Earth's surface to dissolve salt deposits and create a salt brine. This brine is then pumped to the surface and evaporated to create salt. The salty brine may be treated prior to evaporation to reduce mineral content, yielding a nearly pure sodium chloride crystal. This method is inexpensive, has a high yield, and produces a very clean salt. Most table salt is produced with this method.