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A paludier raking halite rafts in coastal pans on the fens of SW France (imaged by Claude Rannou)

Artisanal salt and culinary expectations

Introduction

In 2019, total world production of salt (halite) from both rock-salt and sea-salt was around 300 million tonnes, the top six producers being China (68 million), the United States (42 million), India (29 million), Germany (13 million), Canada (13 million) and Australia (12 million) (Figure 1). In industrialized countries, the proportion of food-grade (edible or table salt) is smaller, generally less than 10% of total production. Worldwide, food usage accounts for some 18% of total salt production. Salt's primary non-food use is as a feedstock to the world's chemical industries, including its use in polyvinyl chloride, plastics, paper pulp and many other industrial products. Other non-food usages include water filtration, de-icing, and a variety of agricultural uses.

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Figure 1. World Salt Production in 2018 in one thousand metric tons (rock-salt and sea-salt combined).
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Figure 2. Salt manufacturing methods A) Salt harvest at Lake Macleod, Australia. B) Salt mine in North America.

Manufacturing food-grade salt

Salt production is one of the world's oldest chemical industries. Today, there are two main manufacturing methods; 1) Production from brine (marine or continental): this requires solar evaporation in arid regions or artificial heating of brine in cooler climes, 2) Mining of ancient salt deposits with subsequent processing of extracted ore (Figure 2).

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Stones cut flat for evaporating seawater to extract salt. Yangpu Ancient Salt Field archeological heritage site in Yantian village, Yangpu Peninsula, Hainan, China (from Wikipedia). The area comprises more than 1,000 stones, cut flat on top, which are used to evaporate seawater to produce salt. The stones have a thin rim around the edge to contain the water. During high tide, the surface of the stones becomes filled with seawater. During low tide, this evaporates, leaving the salt, which is then collected. The area was established around 800 AD when a group of salt workers from Putian city in Fujian province moved to Yangpu. Today, only a small group of villagers continue to make salt using this method, and it is not their primary income. 

To produce salt from seawater, which has a salinity of around 3.5%, requires seawater to be concentrated to roughly ten times its original salinity (to a value of 35% or 350,000 ppm). Accordingly, the world's oceans hold a virtually inexhaustible source of salt. The evaporation of seawater is the production method of choice for edible salt production in countries or regions with climates characterised by high evaporation and low precipitation rates (such as Mexico, Australia, India or Chile). Sea-salt evaporation ponds are first filled with seawater, then cut off from the source. In arid to semiarid climates, the ponds start to desiccate, often as mother brine is pumped through a series of increasingly saline ponds. Salt crystals are harvested from ponds once the brine has reached halite saturation. Sometimes solar pond waters and the raw salt produced can have vivid colours (pink, green or purple), due to various halotolerant and highly pigmented algae and other micro-organisms such as halophilic archaea that thrive in conditions of high salinity (Warren, 2016: Chapter 9).

Elsewhere, in countries and regions with less arid climates salt is extracted from the vast buried sedimentary deposits crystallised by the evaporation of seas and lakes many millions of years ago. These deposits are either mined directly (conventional mining) producing rock salt or are extracted in solution by pumping water into the deposit and processing the recovered brines (solution mining). In either case, the produced salt can be purified by the subsequent dissolution of the rock salt followed by mechanical evaporation and brine processing. Traditionally, brine processing was done in shallow open pans, but more recently, the process is performed in kettles under vacuum (a process known as vacuum evaporation). 

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Salt harvest on Salar di Uyuni, Bolivia

Refining of rock salt and converting it to varieties of edible salt is done to purify, better control crystal texture and moisture content, and improve storage and handling character. The mechanical brine refining process usually involves recrystallisation during which the brine solution is treated with chemicals to selectively remove most impurities from the brine (mostly magnesium and calcium salts) prior to crystallising the final salt product. Multiple stages of mechanical evaporation are then used to collect pure sodium chloride crystals, which are kiln-dried. Some types of edible salt are produced using the Alberger process, which involves vacuum pan evaporation combined with the seeding of the solution with cubic crystals to create a coarser grainy hopper salt marketed as of type flaked salt, which has a price premium.

The Ayoreo, an indigenous group from the Paraguayan Chaco (a huge region of dry scrub forest, rivers and swampland) obtained their salt from ash produced by burning the timber of the Indian salt tree (Maytenus vitisidaea) and other trees. Several hundred years ago, the burning of plant material to make ash was how lye, a hydroxyl form of potassic salt use in soap manufacture, was made. That method gave its name to what today is a broad group of fertiliser salts known as the potash salt, dominated by potassium chloride or potassium sulphate salts, but not including potassic forms of lye (link to potash).

Types of culinary salt

Common-usage edible salt (NaCl) is sold in forms such as sea salt and table salt and usually contains an anti-caking (anti-clumping) agent. Table salt may be iodised to prevent iodine deficiency or fluoridated to avoid tooth decay. Besides household salt's use in cooking and at the table, salt is added in the manufacture of many processed foods. Because of its widespread usage in food preparation and at the table worldwide, defining what scientifically constitutes the named origin of particular forms of edible salt, especially gourmet salts, is not an exact science. With many gourmet varieties caught up in marketing hype, many conflicting descriptions and statements of uniqueness are tied to offering such salts at a price premium (Table 1).

Common or table salt

Table salt is a refined salt containing 97 to 99 percent sodium chloride, along with anti-caking agents such as sodium aluminosilicate or magnesium carbonate to make it free-flowing. Some table salt sold for consumption, and usually labelled as some form of fortified salt, contains additives to address various health concerns, especially in the developing world. The identities and amounts of additives vary widely from country to country. Iodine is an essential micronutrient for humans. A deficiency of the element can cause lowered thyroxine production (hypothyroidism) and enlargement of the thyroid gland (endemic goitre) in adults or cretinism in children. Iodised salt has been used to correct the deficiency since 1924 and consists of 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 stabilise the iodine.

Iodine deficiency affects about two billion people worldwide and is the leading preventable cause of mental retardation. Iodised table salt has significantly reduced disorders of iodine deficiency in countries where it is used. 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 (FDA) recommends 150 micrograms of iodine per day for both men and women. US iodised salt contains 46–77 ppm, whereas in the UK, recommended iodine content of iodised salt is 10–22 ppm.

A "healthy" move away from iodised salt and "non-additive" gurus by well-intentioned but scientifically-challenged middle -class parents, has led to iodine deficiencies in their children in cities such as Melbourne and Sydney, Australia. Children in these affluent suburbs are approaching iodine deficiency levels equivalent to those in some less developed economies of the world, where child populations showing elevated levels of goitre and mental deficiency (Warren, 2016; Chapter 12 for literature summary).

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Table 1. Types of culinary salt

Sodium ferrocyanide, also known as yellow prussiate of soda, is sometimes added to salt as an anti-caking agent. The additive is considered safe for human consumption. 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. The safety of sodium ferrocyanide as a food additive was provisionally acceptable by the Committee on Toxicity in 1988. Other anti-caking 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. The European Union and the United States Food and Drug Administration permit aluminium in the latter two additives.

In "doubly fortified salt", both iodide and iron salts are added. The latter alleviates iron deficiency anaemia, which interferes with the mental development of an estimated 40% of infants in the developing world. A typical iron source is ferrous fumarate. Another additive, especially important for pregnant women, is folic acid (vitamin B9), which gives the table salt a slightly yellow colour. Folic acid helps prevent neural tube defects and anaemia, which affect young mothers, especially in developing countries.

A lack of fluorine in the diet is the cause of a significantly increased incidence of dental caries. Fluoride salts can be added to table salt to reduce tooth decay, especially in countries that have not benefited from fluoridated toothpaste and fluoridated water. The practice is more common in some European countries where water fluoridation is not carried out. In France, 35% of the table salt sold contains added sodium fluoride.

Levels of fluoride added to a water supply or toothpaste is maintained at safe, beneficial levels by government legislation. However, in some tribal regions in the African Rift Valley, the use of salt from natrun crusts (halite plus trona), collected in "naturally precipitated" salt deposits, means the local population is using salt with "naturally elevated" levels of fluorine. The longterm use of such fluoride-rich trona as a food tenderiser has led to widespread fluorosis (mottled teeth and skeletal fluorosis) in the local population (Vuhahula et al. 2009).

Sea Salt and rock salt

Sea salt is typically crystallised by the natural solar evaporation of modern seawater in a series of purpose-built salt ponds. Rock-salt is mined from ancient buried rock beds, first deposited by solar concentration in ancient highly restricted marine embayments and then buried by other rock layers (Table 1).

Raw sea salt for human consumption is made up of individual crystals of various sizes recently precipitated from concentrated seawater. Rock salt has been buried underground, so crystals tend to be made of a fused and cemented impervious crystal mesh. Hence, edible salt from rock salt is manufactured by crushing the original mined rock salt. Today rock salt is often converted to brine and then reprocessed (e.g. vacuum evaporated) to produce various premium-priced salt products with designed ranges of crystal sizes, textures and moisture contents.

Unrefined sea salt contains small amounts of magnesium and calcium halides and sulphates, traces of algal products, salt-resistant bacteria and sediment particles. The calcium and magnesium salts confer a faintly bitter overtone. They make unrefined sea salt hygroscopic and so if stored uncovered, it clumps as it gradually absorbs moisture from the air. Algal products can contribute a mildly "fishy" or "sea-air" odour, the latter from organobromine compounds, while biological pigments can colour the raw salt. Both rock salt and sea salt are available in various coarseness levels and crystal shapes that give a range of "feel in the mouth" textures.

Today, as long as it meets the FDA's purity requirements, salt in the USA that is labelled "sea salt" might not have come from modern sea brines. All mined salt (rock-salt) was originally sea salt since it precipitated from the solar concentration of a marine brine source at some point in the distant past, usually in an isolated evaporating shallow sea (e.g. Himalayan Pink Salt).

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Sea salt manufacturing plant, Tainan, Taiwan

Flaked salt

Flaked salt is a general, non-brand-specific term used to describe edible salt varieties made up of dry, plate-like crystals termed "lamellose salt" in the gourmet world. This salt texture characterises salt rafts made up of flat hopper crystals that grow at the air brine interface (Figures 3, 4, 5a). It is one of the three main textures that typify salt crystallising in any shallow body of brine. The inverted pyramid structure results from supersaturation and differing growth rates between the faces and edges of the crystal (Figure 4). Such pyramid or hopper shapes dominate salt harvested from air-brine interfaces and marketed under names such as River Murray Salt Flakes and Fleur de Sal de Guerande (Figures 4, 5a, b).

According to the local legend, salt flowers Fleur de Sal de Guerande only form on hot days when the wind blows from the east (from the sea). It and the cheaper grey salt (sel gris), which is scraped from the pan floors and prized by gourmands, have been produced this way in French coastal fens since Pre-Roman times.

The flowers of salt are marketed as a "natural" product containing all 84 trace elements and micronutrients found in the sea, and as a natural source of potassium, calcium, copper, zinc and magnesium. This halite product has an intense white colour, with a rigid crunchy crystalline structure and high moisture content giving it a distinct "feel on the tongue." This is because "Fleur de Sel "is composed of clusters of halite rafts. These rafts formed on the brine surface, as a thin layer of floating salt crystals, which are harvested daily via raking and then placed on plastic sheets to dry in the sun, making it a highly labour-intensive product. 

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Figure 3. The three main positions and styles of salt texture crystallising as primary precipitates in a solar salt pond - 1) Bottom nucleates of aligned halite chevrons, 2) Rafts dominated by pyramidal hoppers and 3) Bottom cumulates composed of floundered rafts (after Warren 2016; Chapter 1)
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Figure 4. Salt hopper crystals form as floating inverted pyramids at the air-brine interface (after Warren, 2016; Chapter 1) and are the dominant crystal type in "Fleur de Sel" and Murray River salt flakes.

The "flower of salt" product is packed with no other processing, unlike what happens to industrially-produced sea salt that undergoes a process that typically consists of varying combinations of washing, centrifugation and drying by the heat of combustion, grinding and sieving and the addition of iodine to prevent thyroid problems like goitre. While large saltwork companies need several square kilometres for salt pan installations, a "flower of salt" product can be obtained in ponds with total areas smaller than 0.1 hectares. There is a definite economic upside to the artisanal production of "flowers of salt." Since it is a handmade product, small salterns can be constructed/operated by family groups, offering a new or supplemental income source for low-income populations living in or near hypersaline strandlines.

When rafts become too large to maintain a position at the air-brine interface, they flounder and sink to the pan floor, creating what is known as a cumulate texture (Figure 3). When this form of floundered-raft clay-contaminated salt is collected from the pan floor, it is marketed as sel gris or grey salt (Figure 5c). Ironically, in an industrial sea-salt operation, where salt is harvested to supply a pure and consistent high-grade feedstock to the world's chemical industries, this type of clay-contaminated harvest is known as "black spot." It is to be avoided as it lowers product purity. Black spot indicates a situation where the harvester blades have cut too deep into the salt layer and have picked up material from the original clay pan floor. The use of laser-levelling in industrial salt harvests is designed to avoid this problem. In the gourmet world, collecting a little clay with the product makes sel gris (grey salt) and is marketed at a premium (Table 2).

Flaked salt crystal properties can depend on the artificial technologies used, atmospheric conditions, brine depth and salinity maintenance in natural settings, and yield varying crystal structures and textures in a particular context (Warren, 2016; Chapter 1). Flake salt crystals marketed as varieties of gourmet salt can be made up of irregular salt shavings, pyramidal shapes, hoppers, dendrites and potato chip-like laminated crystals. Mechanically-manufactured flake salts from processed rock salt brine tend to have lower trace mineral contents than natural flake salts, which some gourmets argue gives a stronger salty taste. The large surface area and the low mass of flaked salt gives a crunchy texture in the mouth and a relatively fast dissolution rate.

Pyramidal salt hoppers can also be produced by various mechanical or artificial methods from rocksalt-derived brining followed by slow boiling brine over metal salt pans or evaporating brine in greenhouse solar evaporators (Figure 4). One of the most common artificial processes for pyramidal salt manufacture is the Alberger process. 

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Figure 5. Features of some of the edible salts. A) Salt pans at Le Guerande with halite rafts floating on brine surface and being harvested using a hand-held rake. B) Fleur de Sel (hopper crystals raked from the brine surface). C) Sel Gris (floundered rafts collected from pan bottom where the crystals are mixed with clay to give its characteristic grey colour). D) Namibian Salt pearls (halite ooids collected from the swash zone about the pan edge. E) Bamboo Salt (nine-times pinewood-fired salt. F) Hawaiian Red Salt (seasalt mixed with red volcanic clay). G) Hawaiian Black Lava Salt (charcoal-fired seasalt). H) Himalaya Pink Salt (crushed rocksalt. I) Persian Blue Salt (crushed radiation-damaged rocksalt).

Kosher salt

Kosher salt is coarse-grained salt that is generally not iodised, although some Kosher Salt brands may contain an anti-caking agent. Rather than fine cubic crystals of common table salt, kosher salt is much coarser and has crystals with flattened plate-like shapes compared to crushed fine cubes of common table salt (Figure 6). The Alberger process generally makes the more granulated salt crystals in Kosher Salt to give crystal textures that are more amenable to design. The flattened form is produced when otherwise newly minted cubic crystals are forced into a flatter shape under pressure, usually by passing between rollers. There is a 20-40% price premium for kosher salt compared to ordinary table salt.

The term Kosher Salt gained common usage in North America last century and refers to the salt's use in the Jewish religious practice of dry brining meats—known as koshering. Some salt companies labelled boxes of coarse salt as kosher salt, rather than koshering salt, and the shortened form of the name passed into everyday use. Contrary to popular belief, Kosher Salt does not refer to the salt having to be manufactured under any Jewish religious guidelines. However, some salt brands further identify their kosher-certified salt as being approved by a religious body. It is a common misconception that a rabbi must bless kosher salt, but this is not so, its name simple relates to the process of dry-brining meat.

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Figure 6. Comparison of ordinary table salt and kosher salt

Gourmet salt styles

As well as the range of flaked and kosher salt derived from natural sea salt or mechanically-processed rocksalt brines there are many additional forms of modified and flavoured salt and a few widely marketed and hyped gourmet rocksalt and seasalt products (Table 1; Figure 5).

Bamboo Salt (Jugyeom)

Smoked and flavoured salts are heated and smoked using various woods or bamboo (Figure 5e). For example, Jugyeom (Korean), also known as bamboo salt, is a form of smoked salt prepared by packing sea salt in a thick hollow bamboo stem, then baking it nine times on high temperature over a pinewood fire or kiln (Figure 7a, b) During baking, the salt absorbs the bamboo constituents giving a distinctive sweetness, called Gamrojung flavour. Baking and contamination with organic residues darken the salt, and the ninth baking cycle uses the highest temperature, over 1,000℃. Heating encourages the absorption of various organic products, which means the final bamboo salt contains blue, yellow, red, white, and black hues. Well-baked bamboo salt, with a temperature above 1,500℃, is called "Purple bamboo salt" because of its unique purple colour, which indicates the best quality (Figure 7c). While the quality of bamboo salt cannot be solely determined by colour, its crystal structure and hardness is definitive. The baking method that transforms sea salt into Jugyeom create is also considered by some to make a health food that can slow the growth of some oral cancers.

Kala Namak (Asian Black Salt)

Kala namak or Asian Black Salt is another form of smoked salt, sourced initially from rocksalt from mines in India, Nepal, Pakistan and Bangladesh and salt harvested from the North Indian salt lakes in the Sambhar Salt Lake area and the Didwana and the Mustang Districts of Nepal. More recently it has been marketed as Himalayan Black Salt. Traditionally, salt was transformed from its relatively colourless raw natural form into dark-coloured commercially-sold Kala namak using firing to turns some of the naturally-occurring sodium sulphates in the raw salt into pungent hydrogen sulphide (aka rotten-egg gas) and sodium sulphide.

The raw salt is fired in a kiln or furnace for 24 hours, while sealed in a ceramic jar with charcoal, along with small quantities of harad seeds, amla, bahera, babul bark, and natron. The fired salt melts, chemical reactions with the additives occur, and the salt is then cooled, stored, and aged before sale. Kala namak is still prepared in this manner in northern India with production concentrated in Hisar district, Haryana. Marketed salt crystals appear black and are usually ground to a fine pink powder.

Today much of the manufactures kala namak is synthetically produced. This is done by combining ordinary sodium chloride mixed with smaller quantities of sodium sulphate, sodium bisulphate and ferric sulphate, and then chemically reducing the mixture in the presence of charcoal in a furnace. Reportedly, it is also possible to create similar black salt products through reductive heat treatment of sodium chloride, 5–10% of sodium carbonate, sodium sulphate, and some sugar.

Commercially-available kala namak consists primarily of sodium chloride and trace impurities of sodium sulphate, sodium bisulphate, sodium bisulphite, sodium sulphide, iron sulphide and hydrogen sulphide. Sodium chloride provides the salty taste, iron sulphide provides its dark violet hue, and all the sulphur compounds give kala namak its slight savoury taste as well as a highly distinctive smell, with small amounts of hydrogen sulphide from the breakdown of newly-formed metastable greigite (Fe3S4) being the most prominent contributor to the smell. The acidic bisulphates/bisulphites also contribute a mildly sour taste.

Asian black salt quality (and the types of impurities) varies widely according to the manufacturer's skills and motivation. Depending on the salt source and its additives, some longterm high-level users of some types of Asian Black Salt have been implicated as sufferers of various forms of fluorosis (due to high levels of fluorine).  

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Figure 7. Manufacture of Asian Bamboo Salt (Jugyeom). A) Bamboo stems filled with salt and sealed with clay. B) Placing packed and sealed stems in kiln ready for firing. C) Purple salt created in the ninth burn.
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Salt manufacture from boiling of salt brines at Bo Kluea, Thailand. ZThe brine is sourced in salt wells that tap into the dissolution brines at the crest of shallow diapiric salt structures souced in the Cretaceous Maha Sarakam Fm.

Hawaiian Gourmet Salts (sea salt & mineral or organic additives)

Hawaiian Red Salt (Alaea salt) is made by mixing sea salt with alaea clay, a red Hawaiian volcanic clay rich in iron. Historically it was honoured by the pre-European Island culture for its beauty, health benefits, and spiritual properties. Traditional salt pans used in Alaea Salt's manufacture are small seawater sumps constructed in the volcanic clay of coastal Hawaii, as at Hanapepe on the island of Kauai. Traditional owners hold these pans, and according to local custom the salt produced there cannot be sold. It can only be gifted or traded by the 20 select families that have harvested the salt plots for over five generations at Salt Pond location.

At Hanapepe, seawater from the coastal marine groundwater prism is collected from wells penetrating fractured volcanic aquifers and then held in holding pools, where the seawater becomes concentrated through evaporation. Next, the brine is transferred to shallow harvesting ponds (Figure 8). The amount of time it takes until the salt is ready to be harvested from a shallow pond depends on seasonal factors like precipitation and evaporation rate. Under ideal conditions, it can be as little as two months. Salt is not harvested during the rainy winter months.

During harvest from other commercial ponds, the top, white sea salt is raked, rinsed, and dried. This sea salt flake form is used as table salt. Some of the white sea salt is also mixed with red 'alaea' clay, collected from the nearby mountains of Waimea. The resulting red colour in the salt comes from iron oxides in the clay (Figure 5g). Native Hawaiians believe that "alaea gives the salt spiritual power;" it is used in traditional ceremonies, ritual blessings and purifying, and healing purposes.

Hawaiian Black Lava Salt has a similar sulphur-influenced taste as Kala Namak (but somewhat milder). It is sea salt blended with activated charcoal from coconut shells and fired, with the final product generally used as a finishing salt (Figure 5f). 

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Figure 8. Hanapepe salt ponds on the island of Kauai, Hawaii.
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Himalayan Pink Salt (crushed rock salt)

This premium-priced culinary salt comes from one of the more extensive specific-purpose rocksalt mining operations in the world; the Khewra Salt Mine in the Punjab Region of Pakistan. The mine lies in the Salt Range at the foot of the Himalaya. It targets the pink halokinetically-thrusted 550 million-year-old Salt Range Formation (regionally equivalent to the Hormuz Salt Formation). This geological formation consists of extensively flow-deformed crystalline pink halite (Figure 5h), intercalated with potash salts, overlain by gypsiferous marl and interlayered with beds of gypsum and dolomite with infrequent seams of oil shale (Figure 9; Richards et al., 2015). These strata and the overlying Cambrian to Eocene sedimentary rocks have been thrust southward over younger sedimentary rocks and eroded to create the Salt Range.

Although Himalayan pink salt is sometimes marketed as "Jurassic Sea Salt", this salt precipitated in much older subsiding rift basins along the edge of Gondwanaland some 600 and 540 million years ago The Jurassic period is much younger (199 - 145 million years ago). The characteristic pink colour comes from various mineral impurities, especially iron, and other trace elements.

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Figure 9. Geological detail showing highly sheared and massive nature of Himalayan Pink Salt in the Khewra Salt Mine, Punjab Region, Pakistan. Halite straws, stalactites and efflorescences hang from moisture-etched salt exposed in the partially-dissolved mine roof (see Richards et al. 2015 for further geological detail).

The Khewra salt mine has nineteen levels or storeys, and more the 400 km of passages. Salt is extracted using the room and pillar method, where about half the material is left in place to support the upper levels. Extraction of Himalayan salt from the Khewra salt mine is expected to last 350 years at the present rate of extraction of around 385,000 tons per annum.

Himalayan salt is marketed as a gourmet salt to be used to flavour food. Its distinctive pink hue has led to a misconception amongst some health food fantasists that it is healthier than ordinary table salt. It is not iodine or iron-enriched, unlike some fortified table salt forms, so there are no health advantages. The US Food and Drug Administration has already warned a manufacturer about marketing the pink salt as a dietary supplement by using unproven health benefits claims. Due mainly to marketing and packaging costs, pink Himalayan salt is 30 times more expensive than ordinary table salt or sea salt (Table 2).

As well as the crushed pink rock salt being marketed as a gourmet salt, blocks of Himalayan salt are sold for use as serving dishes, baking stones and griddles. The same pink salt is also used to manufacture salt lamps; wherein light bulbs are placed within hollowed blocks of Himalayan salt to radiate a pinkish hue. Contrary to some marketing claims, there is no evidence that such salt lamps provide any health benefits. Himalayan salt is also used in spas as decoration, but again there is no scientific evidence that using Himalayan Salt in such a way provides any health benefit.

Persian Blue (crushed rock salt)

Persian Blue Salt is a gourmet salt manufactured by grinding blue and white rock-salt extracted from a salt mine in near-surface halokinetic Miocene salt structures in the northern province of Semnan in Iran (Figures 5i, 10). As noted in some gourmet sales materials "... The Persian blue salt has a more intense flavour than other salts. It has a strong initial saltiness and then produces an interesting tingling on the palate with a pleasant, slightly acidic aftertaste – attributable to the high potassium content".

The "intriguing" blue colour in some of the salt crystals (Figure 7) in this crushed rock salt product and the "tingling" in the mouth sensation both indicate the elevated potassium levels. After all, sylvite is a bittern salt, and carnallite (when present micro-inclusions in a salt) gives a highly astringent taste. The extreme astringency of the mineral carnallite and the bitter, salty taste of sylvite are taught to Earth Science students as defining characteristics in Mineralogy 101 classes. The blue colour indicates localised radiation damage in the NaCl lattice structure and is not all that unusual in salt deposits anywhere with high levels of potassium salts nearby. Blue halite is found in many potash fertiliser mines where sylvite or langbeinite ore layers are hosted in halite beds, as in mines in New Mexico, Germany, Poland and Russia. The blue colour is not an interesting "optical illusion," although this is given by some suppliers as the reason for its colour in some of the gourmet literature.

Rather, the blue colour in this type of gourmet halite is indicative of radiation damage, albeit from the presence of radiogenic potassium (40K) at very low levels in the subsurface. Blue radiation-coloured halite is especially common in zones of potassic rock salt subject to intense structural deformation (Zelek et al., 2014). Submitting halokinetic salt to controlled radiation exposure and lattice damage creates blue halite in a nuclear reactor. This is a standard scientific laboratory method to document the deformation evolution in geological samples of flowing (halokinetic) rock salt (e.g. Schléder et al., 2007).

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Figure 10. Blue Persian salt (crushed rock salt and its pre-crushed source (radiation-damaged halite)

Is Gourmet Salt Worth the extra cost?

Some naturally-produced gourmet salt flake varieties (from sea-salt) tend to be less processed than ordinary table salt. The presence of impurities and minute traces of various minerals in a speciality salt can result in slight differences in appearance and flavour. Still, the fact remains that all gourmet salt is essentially sodium chloride.

You can pay from two to fifty times as much for gourmet rock or sea salt as you do for regular table salt in the developed world. Paying a price premium in Australia can get you a salt that's "made by the action of sun and wind on pristine Australian seawater", "harvested from the crystal clear seas on the east coast of Tasmania", "produced from ancient saline waters sourced from underground aquifers found in Australia's Murray Darling basin region", or "handcrafted in small batches". From the same "healthy and organic gourmet suppliers of salt, you can buy pink salt that's "found naturally deep inside the pristine Himalayan Mountains."

Perhaps the most expensive choice of gourmet salt is a flaked salt known as "Fleur de Sel de Guerande", which according to some very effective marketing is also known as the "Celtic Queen of Salts", and the hype continues "...This salt is no imposter as Her Majesty originates from Guerande (just as authentic Champagne is from Champagne, true Fleur de Sel must come from Guerande). According to Celtic tradition, this exceptional salt is hand-harvested and is characterised by highly irregular, relatively fine crystals. The smaller crystals dissolve quickly, while the larger crystals take longer. This salt unravels across your palate in a wave. Many chefs see this salt as the best of all sea salts, because of its elegant appearance, delicate flavour and moist texture."

All gourmet salts are sodium chloride with an overlay of marketing hype and packaging that allows the supplier to charge up to 50 times more than standard or common table salt (Table 2). The distinguishing features of the various gourmet choices compared to common household table salt are mostly based on colour, additives and "feel on the tongue" (crystal size, shape and moisture content).

In general, non-flavoured or smoked gourmet salt varieties tend to be flaked, and many are marketed as "less processed or refined" than ordinary table salt. The presence of impurities and minute traces of various minerals in speciality salt varieties can result in slight differences in appearance and flavour (e.g. Fayet-Moore et al., 2020). Still, the fact remains that all gourmet salt is essentially just sodium chloride with a variety of crystal textures, or in the case of flavoured salts, sodium chloride plus organic or clay or sulphur-based additives introduced to the salt as impurities then dispersed and altered via the introduction of a heat source.

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Table 2. Gourmet Salt Prices in Australia 2020

Health benefits of gourmet salt?

The various untreated salt products from France, the Himalayas and elsewhere are typically marketed as a "natural organic" product, "completely untreated" so it retains all its "essential nutrients." Such blanket claims from marketers targeting a moneyed, health-conscious and "new-age" mostly middle-class demographic, should at times be taken with a grain of salt.

For example, some types of Himalayan "natural" salt, produced from high altitude continental lakes in Tibet, are iodine deficient. "Natural" lake salt consumption in Tibet has led to high levels of cretinism and other thyroid problems in the local peasant population. Some remote mountain villages in Tibet have birthing data that show 13% of newborns suffer from cretinism. This is because of low iodine levels in the soils. Local salt is harvested from salt lakes where glaciation and deep weathering have long ago removed iodine from soils and associated salts. Unlike seasalt, the present soil waters and runoff, which collects and evaporates in the salt lakes, contains little or no iodine (Lee, 2001). When carried to the villages and sold, salt harvested from the Tibetan lakes is 50 % cheaper than salt that has been fortified (sprayed) with iodine. 

Its lower cost makes this local natural salt a more attractive product to Tibetan peasants in the villages, most of whom are subsistence-level farmers. Harvested salt is usually bartered or exchanged for an equivalent weight in rice. To improve the health of the people, selling non-iodised salt has been made illegal by the Chinese government. But a lower price and the fact that the salt harvesters usually barter their salt for an equivalent weight in rice, and have done so for hundreds of years, make the harvested natural salt more attractive than the more expensive iodised product. To maintain their subsistence level livelihoods, the salt harvesters spread and encourage rumours that animals and people fed iodised salt will be infertile.

In rural China and Mongolia, the Chinese government's policy of introducing iodised salt to the rural population has been much more successful than in Tibet's religious regions. In the 1980s the rates of goitre (indicated by an enlarged thyroid and an indicator of iodine deficiency) in China's general population were as high as 40%. By making non-iodised salt illegal and keeping the price of the iodised salt low, the current rate of goitre in the general Chinese population is now somewhere near 5 %. Iodisation programs in salt and milk products in the western world since the 1920s had largely eliminated iodine-deficiency by the 1960s.

Another widely utilised gourmet salt source is a crushed salt mine product, mostly from the Khewra Mine, Pakistan, which is not a completely untreated product but is marketed as a natural salt in many gourmet venues. The reality is it comes out of a salt mine. Then again, an impurity-rich pink salt demands visual attention on a gourmet table. 

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We probably shouldn't believe the health benefit hype of the speciality salt marketers. Australian and most other western consumers eat twice as much salt as we should, mostly in the diet from processed foods. Some gourmet salt suppliers claim their products contain minerals essential to our health, but are they really better for us?

If you Google® "Himalayan salt benefits" you'll find claims that its high mineral content helps improve hydration, balance your body's pH levels, encourage better sleep, support weight loss and hormone balance and more. And the labels of Himalayan salt products allude to multiple benefits too. Chef's Choice Himalayan Pink Rock Salt, for example, boasts of its "high mineral level" and "beneficial minerals." Master of Spices Himalayan Pink Rock Salt speaks of its "rich mineral elements … providing the body with all 84 natural elements it needs". And Equagold Pure High Altitude Himalayan Coarse Pink Salt claims to be "rich in minerals.". But according to most health experts, these types of claims should be … well, taken with a grain of salt.

Jacqui Webster, director of the World Health Organization Collaborating Centre on Population Salt Reduction, The George Institute, told Choice Australia in January 2018 that the beneficial minerals present in Himalayan pink salt are only in minimal amounts. She says,
"Any health benefits from the trace amounts present would be offset by the detriment caused by the associated sodium content. Australians in general already overeat salt, with much of it coming from the packaged food we're eating, so we're better off not adding salt to our food at all."

Some speciality salt suppliers, however, claim to offer a nutritional edge. In the same Choice article, Heart Foundation dietitian Sian Armstrong says,
"From the Heart Foundation's perspective, salt is salt. All different types of salt – whether it's gourmet or table, flakes or rocks – contain sodium, which is the part that's damaging to health.
"Gourmet" salt may, or in some cases does, contain essential minerals, but they're in tiny amounts. To even get close to the recommended daily intake for those minerals you'd need to eat enormous salt amounts, which isn't good for you or even realistic. All of those essential minerals can be found in foods like fresh fruit and vegetables, and it's far better to eat those instead," she adds.

More worryingly, a move away from the food quality control and trace element monitoring maintained by industrial manufacturers of salt to a more "natural" form of salt can at times not just be a harmless response to gourmet hype; it can be downright dangerous. A recent paper by Fayet-Moore et al. (2020) found that the lead (Pb) levels in "Peruvian Pink Salt", widely marketed on gourmet shelves in Australia and worldwide, actually exceeded Food Standard levels. Eating this widely available "natural" pink salt could be quite detrimental.

In Australia, in 2003 the population's iodine intake was half what it was five years earlier. Still, most Australian adults were unaware they were recreating the problem of iodine-deficiency in their children (Li et al., 2001). Based on a more recent 2010 WHO study, it appears the problem in Australia has grown even further (Sydney Morning Herald Newspaper, Oct 10, 2010). The WHO study, which focused on almost all the babies born in Victoria from 2001 to 2006, found clear signs of iodine deficiency in many Australian newborns. About 26,000 of the 368,000 newborns, or about seven per cent, were found to have elevated concentrations of thyroid-stimulating hormone (TSH) caused by the body's compensatory response to an inadequate intake of iodine. A smaller NSW-based study found 5-8 per cent of newborns in that state from 1998 to 2000 were iodine deficient. The WHO considers a population to be iodine-deficient if more than three per cent of neonatal blood samples show elevated TSH concentrations.

New-age anti-science and anti-industrial mantras, now followed by an increasingly scientifically-uninformed proportion of the Australian adult population, have returned the status of Australia's newborn population to that of "iodine deficiency." Some states in Australia are now considering legislation to make iodised flour mandatory in bakery products. 

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Summary

So, in terms of what you are paying a premium for when purchasing gourmet salt, it is generally some form of flaked salt, with its attractiveness mostly related to its interesting "in the mouth" coarse, crunchy texture. You do not get the same "feel in the mouth" with the small crystals that typify ordinary table salt. You can also pay a premium price for culinary additives of various types when you buy a flavoured or smoked salt variety. Or you can buy a "natural sea-blue salt" where the blue colour is undoubtedly a product of nature, but indicates low-level radiation damage to the lattice. A decision on whether a gourmet salt variety is worth up to a 500% price premium, I guess is up to you and your levels of disposable income.

References

Fayet-Moore, F., et al. (2020). "An Analysis of the Mineral Composition of Pink Salt Available in Australia " Foods v. 9, p. 1450-, DOI 10.3390/foods9101490

Richards, L., R. C. King, A. S. Collins, M. Sayab, M. A. Khan, M. Haneef, C. K. Morley, and J. K. Warren, 2015, Macrostructures vs microstructures in evaporite detachments: An example from the Salt Range, Pakistan: Journal of Asian Earth Sciences, v. 113, p. 922-934.

Schléder, Z., S. Burliga, and J. L. Urai, 2007, Dynamic and static recrystallization-related microstructures in halite samples from the Kłodawa salt wall (central Poland) as revealed by gamma-irradiation: Neues Jahrbuch für Mineralogie - Abhandlungen: Journal of Mineralogy and Geochemistry, v. 184, p. 17-28.

Vuhahula, E. A. M., J. R. P. Masalu, L. Mabelya, and W. B. C. Wandwi, 2009, Dental fluorosis in Tanzania Great Rift Valley in relation to fluoride levels in water and in "Magadi" (Trona): Desalination, v. 248, p. 610-615.

Warren, J. K., 2016, Evaporites: A compendium (ISBN 978-3-319-13511-3): Berlin, Springer, 1854 p.

Zelek, S.,Stadnicka, K., Toboła, T., Natkaniec-Nowak, L., 2014,  Lattice deformation of blue halite from Zechstein evaporite basin: Kłodawa Salt Mine, Central Poland: Mineralogy and Petrology v. 108,  p.619-631.

"There was more to upgrade. I went to a shop in downtown Oakland that sold salt of every kind and colour, black and pink and blue. Each variety sat shimmering in a glass canister, priced by the ounce, with a handwritten card recounting its biography: here, salt from the beaches of Gujarat; there, salt from the pans of Brittany; behold, salt from the suburbs of Portland. I backed slowly out the door. I would stick with Diamond Crystal."
Robin Sloan, Sourdough

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