Neither the British government nor the Indian National Congress thought Gandhi’s Dandi March in 1930, held to protest the British tax on salt, would amount to much. But he knew.
When he clasped a fistful of salty mud at Dandi, he said: “With this, I am shaking the foundations of the British Empire.” The protest so energised people that Jawaharlal Nehru later said “it seemed as though a spring had been suddenly released.” Asked by a reporter, “Why salt?” Gandhi replied: “Next to air and water, salt is perhaps the greatest necessity of life.”
Salt is traditionally produced by boiling sea water. About 3.5% of sea water is salt (sodium chloride). But boiling sea water requires energy. So, for millennia, humans have simply captured sea water in shallow pools and allowed it to evaporate over time. This method works best in areas where there is no unseasonal precipitation, and plenty of sunlight. But even in such areas, things are changing.
Microplastics are polluting the oceans. A 2018 study on 39 global salt brands (by researchers in South Korea; published in the journal Environmental Science & Technology) found microplastics in over 90% of the salts surveyed, with the highest levels being recorded in sea salts. Some companies have begun to pass sea water through very fine filters to keep the microplastics out of the salt.
In the sea, salt is found in its dissolved form and must be recrystallised. Rock salt, on the other hand, is found in its crystalline form, in underground salt beds, and can just be sifted, sorted, washed and consumed. These salt beds were formed after sea water, constantly deposited in basins over millions of years, eventually evaporated.
Unrefined salts typically contain other minerals such as calcium sulphate, calcium carbonate and magnesium chloride, some of which taste bitter. So salt-makers use evaporation pans to precipitate these water-soluble minerals out of the mix, to produce salt with a purer flavour.
Processed sea salt ends up being about 98% sodium chloride, and rock salt about 95% sodium chloride, with trace minerals at less than 5%. Still, this is considered highly impure in the eyes of the chemical industry. And that matters, because the largest consumer of salt is not the food industry, at 30% of global volumes produced, but the chemical industry, which comes in at 60% (the remaining 10% goes towards applications such as road de-icing and water purification).
Salt is used to produce chlorine, caustic soda (sodium hydroxide), soda ash (sodium carbonate) and various other chemical compounds used in the manufacture of items ranging from detergents and paper to paints, plastics, batteries and glass. To combat the problem of trace mineral content, salt manufacturers use chemical refining processes and vacuum crystallisation to get salt up to a purity of at least 99.5% sodium chloride.
This mass-produced, purified salt is also sold as common salt (with added iodine). And so it is that common salt is made of tiny, identically shaped crystal cubes. In the presence of moisture, the flat sides of the cubes tend to stick to each other and clump. To prevent this, manufacturers add anti-clumping agents such as silicon dioxide and potassium ferrocyanide, in minute quantities. If you want to avoid anti-clumping agents, look for crystal salts or non-free-flowing salts.
What, then, is low-sodium salt? This is a mix of sodium chloride and other minerals such as potassium chloride or magnesium sulphate, added at levels of 10% to 30% to enhance the salinity without excessive sodium. Before rushing out to buy some, do consider that most of the sodium intake, for the average urban Indian, comes not from their own kitchen but from the processed foods, preserved foods and restaurant foods they consume (think pickles, sauces, chips). In these products, salt serves as both flavour enhancer and preservative. Some food manufacturers are trying to reduce sodium content. But while there is a plethora of sugar substitutes on the market today, the question of how to substitute for salt remains a puzzle. Replace sodium chloride with 100% salt substitutes and it leaves, literally, a bitter taste in the mouth.
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