Salt is a dietary mineral composed primarily of sodium chloride that is essential for animal life, but toxic to most land plants. Salt flavor is one of the basic tastes, and salt is the most popular food seasoning. Salt is also an important preservative.
Salt for human consumption is produced in different forms: unrefined salt (such as sea salt), refined salt (table salt), and iodized salt. It is a crystalline solid, white, pale pink or light gray in color, normally obtained from sea water or rock deposits. Edible rock salts may be slightly grayish in color due to this mineral content.
Chloride and sodium ions, the two major components of salt, are necessary for the survival of all known living creatures, including humans. Salt is involved in regulating the water content (fluid balance) of the body. Salt cravings may be caused by trace mineral deficiencies as well as by a deficiency of sodium chloride itself. Conversely, over consumption of salt increases the risk of health problems, including high blood pressure.
Salt was included among funereal 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 salt fish and salt from North Africa throughout their Mediterranean trade empire.
Along the Sahara, the Tuareg maintain routes especially for the transport of salt by Azalai (salt caravans). In 1960, the caravans still transported some 15,000 tons of salt, but this trade has now declined to roughly a third of this figure.
Salzburg, Hallstatt, and Hallein lie on the river Salzach in central Austria, within a radius of no more than 17 kilometres. Salzach literally means "salt water" and Salzburg "salt city", both taking their names from the Germanic root for salt, salz. Hallstatt literally means "salt town" and Hallein "saltwork", taking their names from hal(l)-, a root for salt found in Celtic, Greek, and Egyptian. The root hal(l)- also gave us Gaul, the Roman exonym for the Celts, Halle and Schwäbisch Hall in Germany, Halych in Ukraine, and Galicia in Spain: this list of places named for Celtic saltworks is far from complete.
Hallstatt gave its name to the Celtic archaeological culture that began mining for salt in the area in around 800 BC Around 400 BC, the Hallstatt Celts, who had heretofore mined for salt, began open pan salt making. During the first millennium BC, Celtic communities grew rich trading salt and salted meat to Ancient Greece and Ancient Rome in exchange for wine and other luxuries.
At times, troops in the Roman army were paid in salt and this is the origin of the words salary and, by way of French, soldier. The word salad literally means "salted," and comes from the ancient Roman practice of salting leaf vegetables.
In the history of Indian Independence, Mahatma Gandhi took a long parade called "Dandi March" or "Salt SathyaGraha" against taxes levied by the then British rulers, for the export of salt, as this would affect the poor "salt-makers". The significance of this announced "March" is that Gandhi never told about his "way" and "destination" till the last moment, and it was a very great success in bringing millions of people together as one.
In Tamil culture, India, "to add salt to food" means that one remains faithful to that household, and also "salt" is considered to increase "senstivity", i.e. it is expected to instigate anger, and aggravate "sense of touch". Salt is also used as a rough method for treating inflammation caused by allergy or insect bites.
Salt is considered to be a very auspicious substance in Hindu mythology, and is used in particular religious ceremonies like house-warming and weddings.
Salt is mandatory in the rite of the Tridentine Mass. Salt is used in the third item (which includes an Exorcism) of the Celtic Consecration (cf. Gallican rite) that is employed in the consecration of a church. Salt may be added to the water "where it is customary" in the Roman Catholic rite of Holy water.
Different natural salts have different mineralities, giving each one a unique flavor. Fleur de sel, natural sea salt harvested by hand, has a unique flavor varying from region to region.
Some advocates for sea salt assert that unrefined sea salt is healthier than refined salts. However, completely raw sea salt is bitter due to magnesium and calcium compounds, and thus is rarely eaten. The refined salt industry cites scientific studies saying that raw sea and rock salts do not contain enough iodine salts to prevent iodine deficiency diseases.
Unrefined sea salts are also commonly used as ingredients in bathing additives and cosmetic products. One example are bath salts, which uses sea salt as its main ingredient and combined with other ingredients used for its healing and therapeutic effects.
Refined salt, which is most widely used presently, is mainly sodium chloride. Food grade salt accounts for only a small part of salt production in industrialised countries (3% in Europe) although world-wide, food uses account for 17.5% of salt production. The majority is sold for industrial use. Salt has great commercial value because it is a necessary ingredient in the manufacturing of many things. A few common examples include: the production of pulp and paper, setting dyes in textiles and fabrics, and the making of soaps and detergents.
The manufacture and use of salt is one of the oldest chemical industries. Salt is also obtained by evaporation of sea water, usually in shallow basins warmed by sunlight; salt so obtained was formerly called bay salt, and is now often called sea salt or solar salt. Today, most refined salt is prepared from rock salt: mineral deposits high in salt. These rock salt deposits were formed by the evaporation of ancient salt lakes, and may be mined conventionally or through the injection of water. Injected water dissolves the salt, and the brine solution can be pumped to the surface where the salt is collected.
After the raw salt is obtained, it is refined to purify it and improve its storage and handling characteristics. Purification usually involves recrystallization. In recrystallization, a brine solution is treated with chemicals that precipitate most impurities (largely magnesium and calcium salts). Multiple stages of evaporation are then used to collect pure sodium chloride crystals, which are kiln-dried.
Since the 1950s it has been common to add a trace of sodium ferrocyanide to the brine; this acts as an anticaking agent by promoting irregular crystals. Other anticaking agents (and potassium iodide, for iodised salt) are generally added after crystallization. These agents are hygroscopic chemicals which absorb humidity, keeping the salt crystals from sticking together. Some anti-caking agents used are tricalcium phosphate, calcium or magnesium carbonates, fatty acid salts (acid salts), magnesium oxide, silicon dioxide, calcium silicate, sodium aluminosilicate, and calcium aluminosilicate. Concerns have been raised regarding the possible toxic effects of aluminium in the latter two compounds; however, both the European Union and the United States Food and Drug Administration (FDA) permit their use. The refined salt is then ready for packing and distribution.
Table salt is refined salt, 99% sodium chloride. It usually contains substances that make it free-flowing (anti-caking agents) such as sodium silicoaluminate or magnesium carbonate. It is common practice to put a few grains of uncooked rice or half a dry cracker (such as Saltine) in salt shakers to absorb extra moisture and help break of clumps when anti-caking agents are not enough. Table salt has a particle density of 2.165 g/cm, and a bulk density (dry, ASTM D 632 gradation) of about 1.154 g/cm.
In many East Asian cultures, salt is not traditionally used as a condiment. However, condiments such as soy sauce, fish sauce and oyster sauce tend to have a high salt content and fill much the same role as a salt-providing table condiment that table salt serves in western cultures.
Iodized salt (BrE: iodised salt) is table salt mixed with a minute amount of potassium iodide, sodium iodide, or iodate. Iodized salt is used to help reduce the incidence of iodine deficiency in humans. Iodine deficiency commonly leads to thyroid gland problems, specifically endemic goiter, a disease characterized by a swelling of the thyroid gland, usually resulting in a bulbous protrusion on the neck. While only tiny quantities of iodine are required in the diet to prevent goiter, the United States Food and Drug Administration recommends (21 CFR 101.9 (c)(8)(iv)) 150 micrograms of iodine per day for both men and women. Iodized table salt has significantly reduced disorders of iodine deficiency in countries where it is used. Iodine is important to prevent the insufficient production of thyroid hormones (hypothyroidism), which can cause goitre, cretinism in children, and myxedema in adults.
Table salt is mainly employed in cooking and as a table condiment. The amount of iodine and the specific iodine compound added to salt varies from country to country. In the United States, iodized salt contains 46-77 ppm, while in the UK the iodine content of iodized salt is recommended to be 10-22 ppm. Today, iodized salt is more common in the United States, Australia and New Zealand than in the United Kingdom.
In some European countries where drinking water fluoridation is not practiced, fluorinated table salt is available. In France, 35% of sold table salt contains either sodium fluoride or potassium fluoride. Another additive, especially important for pregnant women, is Folic acid (Vitamin B9), which gives the table salt a yellow color.
In Canada, at least one brand (Windsor salt) contains invert sugar. The reason for this is unclear.
The risk for disease due to insufficient or excessive salt intake varies due to biochemical individuality. Some have asserted that while the risks of consuming too much salt are real, the risks have been exaggerated for most people, or that the studies done on the consumption of salt can be interpreted in many different ways.
Excess salt consumption has been linked to:
Sea salt (an unrefined form of salt made by evaporating sea water) is often sold for use as a condiment. Because it contains trace amounts of other minerals which are removed in the refining process, it may have health advantages over normal table salt. Certain sea salts are also used in the production of bath salts and cosmetic products.
Rock and sea salt is usually referred and sold as Natrum Muriaticum in homeopathy, and purported by followers to be a deep acting and powerful curative when taken over long periods of time.
Some isolated cultures, such as the Yanomami in South America, have been found to consume little salt, possibly an adaptation originated in the predominantly vegetarian diet of human primate ancestors.
In the United Kingdom the Scientific Advisory Committee on Nutrition (SACN) recommended in 2003 that, for a typical adult, the Reference Nutrient Intake is 4 g salt per day (1.6 g or 70 mmol sodium). However, average adult intake is two and a half times the Reference Nutrient Intake for sodium. SACN states, "The target salt intakes set for adults and children do not represent ideal or optimum consumption levels, but achievable population goals." The Food Safety Authority of Ireland endorses the UK targets.
The NHMRC in Australia was not able to define a recommended dietary intake (RDI). It defines an Adaquate Intake (AI) for adults of 460-920mg/day and an Upper Level of intake (UL) of 2300mg/day. In the United States, the Food and Drug Administration itself does not make a recommendation, but refers readers to Dietary Guidelines for Americans 2005. These suggest that US citizens should consume less than 2,300 mg of sodium (= 2.3 g sodium = 5.8 g salt) per day.
USA: The FDA Food Labeling Guide stipulates whether a food can be labelled as "free", "low", or "reduced/less" in respect of sodium. When other health claims are made about a food (e.g. low in fat, calories, etc.), a disclosure statement is required if the food exceeds 480mg of sodium per 'serving.'
The Menzies Research Institute in Tasmania, Australia, maintains a website dedicated to educating people about the potential problems of a salt-laden diet.
Consensus Action on Salt and Health (CASH) established in 1996, actively campaigns to raise awareness of the harmful health effects of salt. The 2008 focus includes raising awareness of high levels of salt hidden in sweet foods and marketed towards children.
Salt is produced by evaporation of seawater or brine from other sources, such as brine wells and salt lakes, and by mining rock salt, called halite. In 2002, total world production was estimated at 210 million tonnes, the top five producers being the United States (40.3 million tonnes), China (32.9), Germany (17.7), India (14.5), and Canada (12.3). Note that these figures are not just for table salt but for sodium chloride in general.