Salt

• 1. Introduction

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  Salt is a mineral composed primarily of sodium chloride, and around 6000 BC people living in what is now Romania were already boiling spring water to extract it. A salt works in China dates to roughly the same period. This single substance has been prized by the ancient Hebrews, Greeks, Romans, Byzantines, Hittites, Egyptians, and Indians. It has been carried by boat across the Mediterranean and by camel caravan across the Sahara. Nations have gone to war over it. Governments have taxed it. Why would a kitchen seasoning provoke revolutions, finance voyages of exploration, and serve as money in places where coins did not exist? And how does the same compound that flavours a meal also feed the chemical plants that make plastic and paper? The answers run from a Neolithic spring in Romania to a teaspoon on a modern dinner table.

• 2. Currency And Caravans

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  South of the Sahara, salt once functioned as currency, and in Abyssinia slabs of rock salt were used as coins. The Tuareg have traditionally maintained routes across the Sahara specifically for moving salt by Azalai caravans. These caravans still cross the desert from southern Niger to Bilma, though much of the trade now travels by truck. Each camel carries two bales of fodder and two of trade goods northward, returning laden with salt pillars and dates.

  In Gabon, before Europeans arrived, coastal people ran a profitable trade with the interior using sea salt as the medium of exchange. That trade was gradually displaced when Europeans brought salt in sacks, and the coastal people lost their earlier profits. As late as the 1950s, sea salt was still the currency most appreciated in the interior.

  From about 2800 BC, the Egyptians exported salt fish to the Phoenicians in return for Lebanon cedar, glass, and the dye Tyrian purple. The Phoenicians then traded Egyptian salted fish and North African salt across their Mediterranean empire. Herodotus described salt trading routes across Libya in the 5th century BC. Salt may even have been bartered in connection with the obsidian trade in Anatolia during the Neolithic Era, a hint that this mineral underwrote commerce long before written records.

• 3. Salt And Power

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  Venice won the Salt War of 1304 against Padua over the right to supply salt in certain areas, and fought the War of Ferrara from 1482 to 1484 for the same reason. Cities on overland trade routes grew rich by levying duties, and towns like Liverpool flourished on salt exported from the mines of Cheshire. The voyages of Christopher Columbus are said to have been financed from salt production in southern Spain.

  The oppressive salt tax in France was one of the causes of the French Revolution. After being repealed, the tax was reimposed by Napoleon when he became emperor to pay for his foreign wars, and it was not abolished until 1946. The scarcity and universal need for salt also triggered the El Paso Salt War in El Paso in the late 1860s.

  In 1930, Mahatma Gandhi led a crowd of 100,000 protestors on the Dandi March, also called the Salt Satyagraha. Along the way they made their own salt from the sea as a demonstration against the colonial salt tax. This act of civil disobedience inspired numerous Indians and transformed the Indian independence movement into a national struggle. A persistent modern claim that Roman Legions were sometimes paid in salt is baseless, though the word salary does come from the Latin word for salt.

• 4. A Mine Beneath A Lake

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  The largest mine operated by underground workings in the world is the Sifto mine, lying mostly 550 meters below Lake Huron at Goderich, Ontario, in Canada. About seven million tons of salt are extracted from it every year. Away from the sea, salt is taken from vast sedimentary deposits laid down over millennia by the evaporation of ancient seas and lakes. These deposits are either mined directly to produce rock salt, or extracted by pumping water into the deposit.

  The Khewra Salt Mine in Pakistan has nineteen storeys, eleven of them underground, and 400 km of passages. Salt is dug there by the room and pillar method, in which about half the material is left in place to support the upper levels. Extraction of this Himalayan salt is expected to last 350 years at the present rate of around 385,000 tons a year, and the mine draws about a quarter of a million visitors annually as a tourist attraction.

  Seawater offers a different path, with a salinity of approximately 3.5 percent, meaning roughly 35 grams of dissolved salts per kilogram of water. Salt evaporation ponds are filled from the ocean, and crystals are harvested as the water dries. Some of these ponds turn vivid colours, because certain species of algae and other micro-organisms thrive in conditions of high salinity. In 2018, total world production of salt reached 300 million tonnes, with China the top producer at 68 million tonnes, followed by the United States, India, Germany, Canada, and Australia.

• 5. The Industrial Mineral

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  Only a small percentage of the salt manufactured in the world is eaten. Sodium chloride is one of the most widely used inorganic raw materials, serving as a feedstock for caustic soda and chlorine. Those in turn go into PVC, paper pulp, and many other inorganic and organic compounds. Food-grade salt accounts for just 7 percent of production in Europe, though worldwide food uses make up 17.5 percent of the total.

  In the production of aluminium, a layer of melted salt floats on top of the molten metal and removes iron and other contaminants. Salt helps saponify fats in the manufacture of soaps and glycerine, and it acts as an emulsifier in synthetic rubber. In the firing of pottery, salt added to the furnace vaporises before condensing onto the ceramic surface to form a strong glaze.

  When drilling through loose sand or gravel, salt may be added to the drilling fluid to build a stable wall that keeps the hole from collapsing. It works as a mordant in textile dyeing, regenerates resins in water softening, and tans hides. Used as a fertilizer, a moderate concentration of about 1 to 3 grams per litre is considered safe and effective for most plants.

• 6. On The Table

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  Table salt is a refined salt containing about 97 to 99 percent sodium chloride. Anticaking agents such as sodium aluminosilicate or magnesium carbonate are added to keep it free-flowing, and some people drop a few grains of uncooked rice or a saltine cracker into the shaker to absorb moisture and break up clumps. As a flavouring, salt enhances other foods by suppressing their bitterness, making them more palatable and relatively sweeter.

  Before electrically powered refrigeration, salting was one of the main methods of preserving food, and the numbers show its reach. Herring contains 67 mg of sodium per 100 g, while its preserved form, kipper, contains 990 mg. Pork typically holds 63 mg against bacon's 1,480 mg, and potatoes carry 7 mg while potato crisps carry 800 mg per 100 g.

  Unrefined sea salt tells a more complicated story, carrying small amounts of magnesium and calcium halides and sulfates, traces of algal products, salt-resistant bacteria, and sediment particles. The calcium and magnesium salts lend a faintly bitter overtone, and algal products contribute a mildly fishy or sea-air odour. Fleur de sel, gathered from the surface of evaporating brine, carries a distinctive flavour that varies with its source. In traditional Korean cuisine, bamboo salt is made by roasting salt in a bamboo container plugged with mud at both ends, absorbing minerals from the bamboo and the mud. In many East Asian cultures salt is not traditionally a table condiment, its role filled instead by soy sauce, fish sauce, and oyster sauce.

• 7. Health And Deficiency

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  The World Health Organization recommends that adults consume less than 2,000 mg of sodium, the amount contained in 5 grams of salt, per day. Table salt is just under 40 percent sodium by weight, so a single 6 g teaspoon delivers about 2,400 mg of sodium. In the United States, 75 percent of the sodium people eat comes from processed and restaurant foods, with 11 percent from cooking and table use and the rest occurring naturally.

  High sodium intake raises the risk of stroke, cardiovascular disease, and kidney disease, and a reduction of 1,000 mg per day may cut cardiovascular disease by about 30 percent. The relationship is not simple, though. One description holds that the association between sodium consumption and cardiovascular disease or mortality is U-shaped, with increased risk at both high and low intake. Increased mortality from excessive salt was primarily associated with people who had hypertension.

  Salt also addresses deficiencies that quietly damage health. Iodized salt has corrected iodine-related conditions since 1924, mixing table salt with a minute amount of potassium iodide, sodium iodide, or sodium iodate. Iodine deficiency affects about two billion people worldwide and is the leading preventable cause of intellectual disabilities. Doubly fortified salt adds iron to relieve the iron deficiency anaemia that interferes with the mental development of an estimated 40 percent of infants in the developing world. In France, 35 percent of the table salt sold contains added sodium fluoride to fight tooth decay.

• 8. Sacred Salt

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  When Lot's wife looked back at the destruction of Sodom and Gomorrah, the Bible says she was turned into a pillar of salt. In the New Testament, Jesus calls his followers the salt of the earth. The Bible also records the practice of salting the earth, scattering salt around a defeated city to symbolically prevent plant growth, as King Abimelech was ordered to do at Shechem.

  At Brahmanic sacrifices, in Hittite rituals, and during new-moon festivals held by Semites and Greeks, salt was thrown into a fire where it crackled. The ancient Egyptians, Greeks, and Romans invoked their gods with offerings of salt and water, which some think is the origin of Holy Water in the Christian faith. In Judaism, Jews dip the Sabbath bread in salt to preserve the covenant between their people and God, recalling the covenant of salt their ancestors made by sprinkling salt on their offerings.

  Salt is mandatory in the rite of the Tridentine Mass and is used in the Celtic Consecration of a church. In Aztec mythology, Huixtocihuatl was a fertility goddess who presided over salt and salt water. In Mahayana Buddhist tradition salt is believed to ward off evil spirits, so a pinch is thrown over the left shoulder when returning home from a funeral. In Shinto, salt purifies locations and people, and small piles of it are placed by entrances both to ward off evil and to attract patrons.