Salt

In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as rock salt or halite. Salt is essential for life in general (being the source of the essential dietary minerals sodium and chlorine), and saltiness is one of the basic human tastes. Salt is one of the oldest and most ubiquitous food seasonings, and is known to uniformly improve the taste perception of food. Salting, brining, and pickling are ancient and important methods of food preservation.

Some of the earliest evidence of salt processing dates to around 6000 BC, when people living in the area of present-day Romania boiled spring water to extract salts; a salt works in China dates to approximately the same period. Salt was prized by the ancient Hebrews, Greeks, Romans, Byzantines, Hittites, Egyptians, and Indians. Salt became an important article of trade and was transported by boat across the Mediterranean Sea, along specially built salt roads, and across the Sahara on camel caravans. The scarcity and universal need for salt have led nations to go to war over it and use it to raise tax revenues, for instance triggering the El Paso Salt War which took place in El Paso in the late 1860s. Salt is used in religious ceremonies and has other cultural and traditional significance.

Salt is processed from salt mines, and by the evaporation of seawater (sea salt) and mineral-rich spring water in shallow pools. The greatest single use for salt (sodium chloride) is as a feedstock for the production of chemicals. It is used to produce caustic soda and chlorine, and in the manufacture of products such as polyvinyl chloride, plastics, and paper pulp. Of the annual global production of around three hundred million tonnes, only a small percentage is used for human consumption. Other uses include water conditioning processes, de-icing highways, and agricultural use. Edible salt is sold in forms such as sea salt and table salt. Table salt usually contains an anti-caking agent and may be iodised to prevent iodine deficiency. As well as its use in cooking and at the table, salt is present in many processed foods.

Sodium is an essential element for human health via its role as an electrolyte and osmotic solute. However, excessive salt consumption increases the risk of cardiovascular diseases such as hypertension. Such health effects of salt have long been studied. Numerous world health associations and experts in developed countries recommend reducing consumption of popular salty foods. The World Health Organization recommends that adults consume less than 2,000 mg of sodium, equivalent to 5 grams of salt, per day.

All through history, the availability of salt has been pivotal to civilization. What is now thought to have been the first city in Europe is Solnitsata, in Bulgaria, which was a salt mine, providing the area now known as the Balkans with salt since 5400 BC. Salt was the best-known food preservative, especially for meat, for many thousands of years. A very ancient salt-works operation has been discovered at the Poiana Slatinei archaeological site next to a salt spring in Lunca, Neamț County, Romania. Evidence indicates that Neolithic people of the Precucuteni Culture were boiling the salt-laden spring water through the process of briquetage to extract salt as far back as 6050 BC. The salt extracted from this operation may have directly correlated with the rapid growth of this society's population soon after production began. The harvest of salt from the surface of Xiechi Lake near Yuncheng in Shanxi, China, dates back to at least 6000 BC, making it one of the oldest verifiable saltworks.

There is more salt in animal tissues, such as meat, blood, and milk, than in plant tissues. Nomads who subsist on their flocks and herds do not eat salt with their food, but agriculturalists, feeding mainly on cereals and vegetable matter, need to supplement their diet with salt. With the spread of civilization, salt became one of the world's main trading commodities. It was of high value to the ancient Hebrews, the Greeks, the Romans, the Byzantines, the Hittites and other peoples of antiquity. In the Middle East, salt was used to seal an agreement ceremonially, and the ancient Hebrews made a "covenant of salt" with God and sprinkled salt on their offerings to show their trust in him.

An ancient practice in time of war was salting the earth: scattering salt around in a defeated city to symbolically prevent plant growth. The Bible tells the story of King Abimelech who was ordered by God to do this at Shechem. Texts claim that the Roman general Scipio Aemilianus Africanus ploughed over and sowed the city of Carthage with salt after it was defeated in the Third Punic War (146 BC), although this story is now considered to be entirely apocryphal.

Salt may have been used for barter in connection with the obsidian trade in Anatolia in the Neolithic Era. Salt was included among funeral offerings found in ancient Egyptian tombs from the third millennium BC, as were salted birds, and salt fish. From about 2800 BC, the Egyptians began exporting salt fish to the Phoenicians in return for Lebanon cedar, glass, and the dye Tyrian purple. The Phoenicians traded Egyptian salted fish and salt from North Africa throughout their Mediterranean trade empire. Herodotus described salt trading routes across Libya back in the 5th century BC. In the early years of the Roman Empire, roads were built for the transportation of salt from the salt imported at Ostia to the capital.