Salt

Halite crystals, commonly known as rock salt

Brine Ancient method of boiling brine into pure salt in Bo Kluea District Nan Province, Thailand

Brine being boiled down to produce salt at the Xinhai Well in Zigong, People's Republic of China

A salt evaporation pond in Tamil Nadu, India.

Evaporation pans in the 'Salt Valley' of Añana, Spain

Salt, also known as table salt or rock salt (halite), is a crystalline mineral that is composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of ionic salts. It is absolutely essential for animal life, but can be harmful to animals and plants in excess. Salt is one of the oldest, most ubiquitous food seasonings and salting is an important method of food preservation. The taste of salt (saltiness) is one of the basic human tastes.

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 because of mineral content.

Because of its importance to survival, salt has often been considered a valuable commodity during human history. However, as salt consumption has increased during modern times, scientists have become aware of the health risks associated with high salt intake, including high blood pressure in sensitive individuals. Therefore, some health authorities have recommended limitations of dietary sodium, although others state the risk is minimal for typical western diets.

History

Salt production in Halle, Saxony-Anhalt (1670)

Sea salt harvesting in Pak Thale, Phetchaburi, Thailand

While people have used canning and artificial refrigeration to preserve food for the last hundred years or so, salt has been the best-known food preservative, especially for meat, for many thousands of years.^[1] A very ancient saltworks operation has been discovered at the Poiana Slatinei archaeological site next to a salt spring in Lunca, Neamţ 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 the salt as far back as 6050 BC.^[2] The salt extracted from this operation may have had a direct correlation to the rapid growth of this society's population soon after its initial production began.^[3] 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.^[4]:18–19

Salt was included among funeral offerings found in ancient Egyptian tombs from the third millennium BC, as were salted birds and salt fish.^[4]:38 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.^[4]:44

In Africa, the Tuareg have traditionally maintained routes across the Sahara especially for the transportation of salt by Azalai (salt caravans). In 1960, the caravans still carried some 15,000 tons of salt a year but this trade has now declined to roughly a third of that figure.^[5]

Salzburg, Hallstatt, and Hallein lie within 17 kilometers (11 mi) of each other on the river Salzach in central Austria in an area with extensive salt deposits. Salzach literally means "salt water" and Salzburg "salt city", both taking their names from the German word Salz meaning salt. The equivalent Celtic word was Hall, and Hallstatt was the site of the world's first salt mine.^[6] The town gave its name to the Hallstatt culture that began mining for salt in the area in about 800 BC. Around 400 BC, the townsfolk, who had previously used pickaxes and shovels, 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.^[1] The word salary originates from Latin: salarium which referred to the money paid to the Roman Army's soldiers for the purchase of salt.^[7][8][9] The word salad literally means "salted", and comes from the ancient Roman practice of salting leaf vegetables.^[4]:64

In 1930, Mahatma Gandhi led at least 100,000 people on the "Dandi March" or "Salt Satyagraha", in which protesters made their own salt from the sea, which was illegal under British rule, as it avoided paying the "salt tax". This civil disobedience inspired millions of common people, and elevated the Indian independence movement from an elitist struggle to a national struggle.^[10]

Forms

Unrefined

Different natural salts have different mineralities depending on their source, giving each one a unique flavor. Fleur de sel, a natural sea salt from the surface of evaporating brine in salt pans, has a unique flavor varying with the region from which it is produced. In traditional Korean cuisine, so-called "bamboo salt" is prepared by roasting salt^[11] in a bamboo container plugged with mud at both ends. This product absorbs minerals from the bamboo and the mud, and has been claimed to increase the anticlastogenic and antimutagenic properties of doenjang (a fermented bean paste).^[12]

Unrefined sea salt contains small amounts of magnesium and calcium halides and sulfates, traces of algal products, salt-resistant bacteria, and sediment particles.^[13] The calcium/magnesium salts make unrefined sea salt hygroscopic (it gradually absorbs moisture from air if stored uncovered) and confer a faintly bitter overtone. Algal products contribute a mildly "fishy" or "sea-air" odor, the latter from organobromine compounds. Sediments, the proportion of which varies with the source, give the salt a dull gray appearance. Since taste and aroma compounds are often detectable by humans in minute concentrations, sea salt may have a more complex flavor than pure sodium chloride when sprinkled on top of food. When salt is added during cooking however, these flavors would likely be overwhelmed by those of the food ingredients.^[13]

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.^[14]

Refined

Salt mounds in Salar de Uyuni, Bolivia

Refined salt, the most widely used form, is mainly composed of sodium chloride. Food grade salt accounts for only a small part of salt production in industrialized countries (3 percent in Europe)^[15] although worldwide, food uses account for 17.5 percent of salt production.^[16] The main bulk is sold for industrial use where it has great commercial value as a necessary ingredient in many manufacturing processes. A few common examples include the production of pulp and paper, the use as a mordant in the dyeing of textiles and the making of soaps and detergents.^[17]

The manufacture and use of salt is one of the oldest chemical industries.^[18] Salt can be obtained by evaporation of sea water, usually in shallow basins warmed by sunlight;^[19] salt so obtained was formerly called bay salt, and is now often called sea salt or solar salt. Rock salt deposits are formed by the evaporation of ancient salt lakes,^[20] 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. The raw salt is then refined to purify it and improve its storage and handling characteristics. Purification usually involves recrystallization. In this process, 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.^[21]

Jagged salt pinnacles at the Devil's Golf Course in Death Valley National Park, US formed by the evaporation of an ancient lake

Table salt

In many cuisines around the world, salt is used in cooking, and is often found in salt shakers on diners' eating tables for their personal use on food. Table salt is refined salt, which contains about 97 to 99 percent sodium chloride.^[22][23][24] It usually contains additives that make it free-flowing, anticaking agents such as sodium aluminosilicate or magnesium carbonate. Some people put a desiccant, such as a few grains of uncooked rice^[25] or a saltine cracker,^[26] in their salt shakers to absorb extra moisture and help break up salt clumps that may otherwise form. Table salt has a particle density of 2.165 g/cm³, and a bulk density (dry, ASTM D 632 gradation) of about 1.154 g/cm³.^[27]

Additives

Most table salt sold for consumption contain additives which address a variety of health concerns, especially in the developing world. The identities and amounts of additives vary widely from country to country.

Iodine and iodide

Iodine is important to prevent the insufficient production of thyroid hormones (hypothyroidism), which can cause goiter, cretinism in children, and myxedema in adults.^[28] Iodine-containing compounds are added to table salt. Iodized salt is thus table salt mixed with a minute amount of potassium iodide, sodium iodide, or sodium iodate. A small amount of dextrose may also be added to stabilize the iodine.^[29]

Iodized salt is used to help reduce the incidence of iodine deficiency in humans. Iodine deficiency affects about two billion people and is the leading preventable cause of mental retardation.^[30] The practice began in 1924.^[31] 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. Iodized table salt has significantly reduced disorders of iodine deficiency in countries where it is used.^[32]

The amount of iodine and the specific iodine compound added to salt varies from country to country. In the United States, the Food and Drug Administration recommends [21 CFR 101.9 (c)(8)(iv)] 150 micrograms of iodine per day for both men and women. US iodized salt contains 46–77 ppm (parts per million), whereas in the UK the iodine content of iodized salt is recommended to be 10–22 ppm.^[33]

Fluoride

A lack of fluorine in the diet is the cause of a greatly increased incidence of dental caries.^[34] Fluoride salts can be added to table salt with the goal of reducing tooth decay, especially in countries that have not benefited from fluoridated toothpastes and fluoridated water. The practice is more common in some European countries where water fluoridation is not carried out. In France, 35 percent of the table salt sold contains added sodium fluoride.^[35]

Anti-caking agents

Sodium ferrocyanide, also known as yellow prussiate of soda, is sometimes added to salt as an anticaking agent. The additive is considered safe for human consumption.^[36][37] Such anti-caking agents have been added since at least 1911 when magnesium carbonate was first added to salt to make it flow more freely.^[38] The safety of sodium ferrocyanide as a food additive was found to be provisionally acceptable by the Committee on Toxicity in 1988.^[36] Other anticaking agents sometimes used include tricalcium phosphate, calcium or magnesium carbonates, fatty acid salts (acid salts), magnesium oxide, silicon dioxide, calcium silicate, sodium aluminosilicate, and calcium aluminosilicate. Both the European Union and the United States Food and Drug Administration (FDA) permitted the use of aluminum in the latter two compounds.^[39]

Iron

In "doubly fortified salt", both iodide and iron salts are added. This additive alleviates iron deficiency anemia, which interferes with the mental development of an estimated 40 percent of infants in the developing world. A typical iron source is ferrous fumarate.^[35]

Other additives

Another additive, especially important for pregnant women, is folic acid (vitamin B₉), which gives the table salt a yellow color. Folic acid helps prevent neural tube defects (NTDs) and anemia, which affect young mothers, especially in developing countries.^[35]

Salty condiments

In many East Asian cultures, salt is not traditionally used as a condiment.^[40] In its place, condiments such as soy sauce, fish sauce and oyster sauce tend to have a high sodium content and fill a similar role to table salt in western cultures. They are most often used for cooking rather than as table condiments.^[41]

Health effects

SEM image of a grain of table salt

Chloride and sodium ions, the two major components of salt, are needed by all known living creatures in small quantities. Salt is involved in regulating the water content (fluid balance) of the body. The sodium ion itself is used for electrical signaling in the nervous system.^[42]

Salt consumption has increased during modern times and scientists have become aware of the health risks associated with high salt intake, including high blood pressure in sensitive individuals. Therefore, some health authorities have recommended limitations of dietary sodium, although others state the risk is minimal for typical western diets.^{[43][44][45][46][47]} The United States Department of Health and Human Services recommends that individuals consume no more than 1500–2300 mg of sodium (3750–5750 mg of salt) per day depending on age.^[48]

Salt is sometimes used as a health aid, such as a high salt diet being used in the treatment of dysautonomia.^[49]

Acute effects

Too much or too little salt in the diet can lead to muscle cramps, dizziness, or electrolyte disturbance, which can cause neurological problems, or death.^[50] Drinking too much water, with insufficient salt intake, puts a person at risk of water intoxication (hyponatremia).^[51]

Death can occur by ingestion of large amounts of salt in a short time (about 1 g per kg of body weight).^[52] Deaths have also resulted from attempted use of salt solutions as emetics, forced salt intake, and accidental confusion of salt with sugar in child food.^[53]

Long-term effects

The effect of salt consumption on long term health outcomes is controversial.^[54] Some associations include:

• Stroke and cardiovascular disease.^[55]
• High blood pressure: Evidence shows an association between salt intakes and blood pressure among different populations and age range in adults.^[56] Reduced salt intake also results in a small reduction in blood pressure.^[54]
• Left ventricular hypertrophy (cardiac enlargement): "Evidence suggests that high salt intake causes left ventricular hypertrophy, a strong risk factor for cardiovascular disease, independently of blood pressure effects."^[56] "...there is accumulating evidence that high salt intake predicts left ventricular hypertrophy."^[57] Excessive salt (sodium) intake, combined with an inadequate intake of water, can cause hypernatremia. It can exacerbate renal disease.^[50]
• Edema: A decrease in salt intake has been suggested to treat edema (fluid retention).^[50][58]
• Stomach cancer is associated with high levels of sodium, "but the evidence does not generally relate to foods typically consumed in the UK."^[59] However, in Japan, salt consumption is higher.^[60]

However, a meta-analysis published in The Journal of Hypertension found no strong evidence that reducing salt intake affects the risk of heart attack, stroke or death in people with normal or high blood pressure.^[61] Furthermore, the Journal of the American Medical Association has reported that those excreting less salt (thus, presumably ingesting less) were at increased risk of dying from heart disease.^[61]

A salt mill for sea salt

In 1994, the British Medical Journal published a randomized double blind, placebo controlled study examining 100 Dutch middle-aged and elderly subjects with mild to moderate hypertension. A low sodium, high potassium, high magnesium mineral salt was used at the table and in foods given to the intervention group, with the control group using ordinary table salt in their foods and at the table. Over a 24-week period, the researchers found a reduced blood pressure in the intervention group, with mean blood pressure falling by 7.6 mm Hg (systolic) and 3.3 mm Hg (diastolic) in the mineral salt group compared with the control group.^[62] However, critics have pointed out that it is possible that some of the subjects may have changed their dietary habits due to being able to distinguish the mineral salt from table salt because of the difference in taste.^[63]

According to The Mayo Clinic and Australian Professor Bruce Neal, the health consequences of ingesting sea salt or regular table salt are the same, as the content of sea salt is still mainly sodium chloride.^[64][65]

Recommended intake

Recommended intakes of salt are usually expressed in terms of sodium intake. Salt (as sodium chloride) contains 39.3 percent of sodium by weight.

A 2009 meta-analysis found that the sodium consumption of 19,151 individuals from 33 countries fit into the narrow range of 2,700 to 4,900 mg/day. The small range across many cultures, together with animal studies, suggest that sodium intake is tightly controlled by feedback loops in the body, making recommendations to reduce sodium consumption below 2,700 mg/day potentially futile.^[72]

Labeling

UK: The Food Standards Agency defines the level of salt in foods as follows: "High is more than 1.5 g salt per 100 g (or 0.6 g sodium). Low is 0.3 g salt or less per 100 g (or 0.1 g sodium). If the amount of salt per 100 g is in between these figures, then that is a medium level of salt." In the UK, foods produced by some supermarkets and manufacturers have 'traffic light' colors on the front of the pack: red (high), amber (medium), or green (low).^[73]

USA: The FDA Food Labeling Guide stipulates whether a food can be labeled 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 480 mg of sodium per 'serving'.^[74]

Campaigns

Consensus Action on Salt and Health (CASH)^[75] established in the United Kingdom 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 that are marketed towards children.^[76] In 2004, Britain's Food Standards Agency started a public health campaign called "Salt – Watch it", which recommends no more than 6g of salt per day; it features a character called Sid the Slug and was criticised by the Salt Manufacturers Association (SMA).^[77] The Advertising Standards Authority did not uphold the SMA complaint in its adjudication.^[78] In March 2007, the FSA launched the third phase of their campaign with the slogan "Salt. Is your food full of it?" fronted by comedienne Jenny Eclair.^[79]

The University of Tasmania's Menzies Research Institute maintains a website to educate people about the problems of a salt-laden diet.^[80] In Australia, the "Drop the Salt! Campaign" aimed to reduce the consumption of salt by Australians to 6g per day over the course of five years ending in 2012.^[81]

In January 2010, New York City launched the National Salt Reduction Initiative, modeled after an initiative in the United Kingdom. The campaign calls on food makers to voluntarily reduce the amount of sodium in their foods, from 20 percent reduction in peanut butter to a 40 percent reduction in canned vegetables, with an overall goal of reducing sodium in packaged and restaurant foods by 25 percent by 2015.^[82] A number of major food producers have taken up the challenge and pledged to reduce the sodium content of their food. Pepsi is developing a "designer salt" that's slightly more powdery than the salt it regularly uses. The company hopes this new form of salt will cut sodium levels by 25 percent in its Lay's potato chips.^[83] Nestlé's prepared foods company, which produces frozen meals, announced that it will reduce sodium in its foods by 10 percent by 2015.^[84] General Mills announced that it will reduce the sodium content of 40 percent of its foods by about 20 percent by 2015.^[85]

In the United States, taxation of sodium has been proposed as a method of decreasing sodium intake and thereby improving health in countries where typical salt consumption is high.^[86][87] Taking an alternative view, the Salt Institute, a salt industry body based in North America, is active in promoting the use of salt,^[88] and questioning or opposing the recommended restrictions on salt intake.^[89]

Lowering salt in diet

It is a misconception that sea salt has a lower sodium content than table salt, — they are both basically sodium chloride.^[64][90][91] A low sodium diet reduces the intake of sodium by the careful selection of food. This aim can also be achieved by the use of a salt substitute, and Potassium chloride is widely used for this purpose. Although recommended limits for potassium are higher than for sodium, potassium has its own health disadvantages, and it is advised that such a salt substitute not be used by those taking certain prescription drugs.^[92] Another possibility being researched is the use of seaweed granules in the manufacture of processed foods as an alternative to salt.^[93]

Production

Global salt output in 2005

The world's oceans are a virtually inexhaustible source of salt and this abundance of supply means that reserves have not been calculated.^[94] The evaporation of seawater is the method of choice in areas of high evaporation and low precipitation. Elsewhere salt is extracted from the vast sedimentary deposits which have been laid down over the millennia from the evaporation of seas and lakes. These are either mined direct, producing rock salt (halite), or are extracted in solution by pumping water into the deposit. In either case the salt may be purified by mechanical evaporation in pans under vacuum.^[95]

In 2002, total world production (of sodium chloride in general, not just table salt) 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).^[96] During the period 2003 to 2008, global production of salt increased by 12% per year, and China took over as the largest producing nation as its chemical industry expanded.^[94]

Ship loading salt at a terminal in the Port of Areia Branca, Brazil

Non-dietary uses

Apart from its use in the human diet, sodium chloride is widely used in industry and is one of the largest inorganic raw materials used by volume. Its major chemical products are caustic soda and chlorine and these are used in the manufacture of PVC, plastics, paper pulp and many other inorganic and organic compounds. Salt itself is used as a food preservative, flavouring agent, in minerals for livestock, for de-icing, for snow control, as a water softening agent and in many industrial processes.^[94][95]

Usage in religion

The Dead Sea is said to be the site of Sodom and Gomorrah. The salt concentration in it is so high that it allows the body to float high in the water

In the Hebrew Bible, thirty-five verses mention salt, ^[97] one of which being the story of Lot's wife, who was turned into a pillar of salt when she looked back at the cities of Sodom and Gomorrah (Genesis 19:26) as they were destroyed. When the judge Abimelech destroyed the city of Shechem, he is said to have "sown salt on it," probably as a curse on anyone who would re-inhabit it (Judges 9:45). The Book of Job contains the first mention of salt as a condiment. "Can that which is unsavoury be eaten without salt? or is there any taste in the white of an egg?" (Job 6:6)^[97]

In the Christian New Testament, six verses mention salt. In the Sermon on the Mount, Jesus referred to his followers as the "salt of the earth". The apostle Paul also encouraged Christians to "let your conversation be always full of grace, seasoned with salt" (Colossians 4:6).^[97]

Salt is mandatory in the rite of the Tridentine Mass.^[98] 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.^[98]

In Judaism, it is recommended to have either a salty bread or to add salt to the bread if this bread is unsalted when doing Kiddush for Shabbat. It is customary to spread some salt over the bread or to dip the bread in a little salt when passing the bread around the table after the Kiddush.^[99] To preserve the covenant between their people and God, Jews dip the Sabbath bread in salt.^[100]

In one of the Hadith recorded in Sunan Ibn Majah, the Islamic Prophet Muhammad is reported to have said that: "Salt is the master of your food. God sent down four blessings from the sky – fire, water, iron and salt".^[101]

Salt is considered to be a very auspicious substance in Hinduism and is used in particular religious ceremonies like housewarmings and weddings.^[101] In Jainism, devotees offer raw rice and a pinch of salt before a deity to signify their devotion and it is sprinkled on a person's cremated remains before the ashes are buried. ^[102]

In Wicca, salt is symbolic of the element Earth. It is also believed to cleanse an area of harmful or negative energies. A dish of salt and a dish of water are almost always present on an altar. The salt is mixed with the water to consecrate it, in effect producing holy water. This mixture is used in a wide variety of rituals and ceremonies.^[103]

In the native Japanese religion Shinto, salt is used for ritual purification of locations and people (harae, specifically shubatsu), such as in sumo wrestling, and small piles of salt called morijio (盛り塩, pile of salt) or shiobana (塩花, salt flowers) are placed in dishes by the entrance of establishments for the two-fold purposes of warding off evil and attracting patrons.^[104]

In Aztec mythology, Huixtocihuatl was a fertility goddess who presided over salt and salt water.^[105]

The ancient Egyptians, Greeks and Romans invoked their gods with offerings of salt and water. Some think this to be the origin of Holy Water in the Christian faith.^[100]

See also

• Alberger process
• Black salt (disambiguation)
• Health Canada Sodium Working Group
• Intersalt study
• Kosher salt
• Salt equivalent
• Salt road
• Smoked salt
• Salted earth

Notes

References

• Barber, Elizabeth Wayland (1999). The Mummies of Ürümchi. New York: W.W. Norton & Co. ISBN 0-393-32019-7. OCLC 48426519. 
• Kurlansky, Mark (2002). Salt: A World History. New York: Walker & Co. ISBN 0-8027-1373-4. OCLC 48573453. 
• Carusi, Cristina, Il sale nel mondo greco, VI a.C.-III d.C.: luoghi di produzione, circolazione commerciale, regimi di sfruttamento nel contesto del Mediterraneo antico (Bari: Edipuglia, 2008) (Pragmateiai; 15).

Further reading

• Alden, Lori (2005). "Salt". The Cook's Thesaurus. 
• Cowen, Richard (May 1999). "The Importance of Salt". UC Davis Department of Geology. 
• Zacharias, Patricia (23 January 2000). "The ghostly salt city beneath Detroit". The Detroit News. 
• Gary Taubes (2 June 2012). "Salt, We Misjudged You". The New York Times. 
• Committee on Strategies to Reduce Sodium Intake (2010). Henry, Jane E ; Taylor, Christine L, ed. Strategies to Reduce Sodium Intake in the United States. Washington, DC: The National Academies Press. ISBN 978-0-309-14805-4. Lay summary – The National Academies (20 April 2010). 
• Panel on Dietary Reference Intakes for Electrolytes and Water (2005). Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: The National Academies Press. ISBN 978-0-309-09158-9. Lay summary – The National Academies (11 February 2004). 

External links

• International Council for the Control of Iodine Deficiency Disorders
• Salt Institute