Science Fair Project Encyclopedia
- For sour salt, see: calcium citrate.
Edible salt is a mineral, one of the few rocks people eat. There are different forms of it: unrefined salt, refined salt, table salt or iodised salt. It is a crystalline solid, white, pale pink or light grey in colour, obtained from seawater or from rock deposits. Sea salt comes in fine or larger crystals. In nature it includes not only sodium chloride, but also other vital trace minerals. Edible rock salts may be slightly greyish in colour due to trace mineral content. Salt is necessary for the survival of all living creatures, including humans. Salt is involved in regulating the water content (fluid balance) of the body. Salt flavor is one of the basic tastes. Salt cravings may be caused by trace mineral deficiencies as well as by a deficiency of sodium chloride itself.
History of edible salt
- For the history of salt in America, see History of salt in America.
In the past, salt was difficult to obtain, but had a great importance in food preservation and as a vital food additive. Therefore, it was a highly valued trade item throughout history. Wars were fought over it, states were formed and destroyed because of it.
Roman soldiers were partially paid with salt, and this is still evident in the English language as the word salary derives from the Latin word salarium that means payment in salt (Latin sal), as well as the phrase "worth one's salt". It was also of high value to the Hebrews, Greeks and other peoples of antiquity.
During the late Roman Empire and throughout the Middle Ages salt was a precious commodity carried along the salt roads into the heartland of the Germanic tribes. Cites, states and dukedoms along the salt roads exacted heavy duties and taxes for the salt passing through their territories. This practise has caused wars, it even caused the formation of cities such as the city of Munich in 1158 when the then Duke of Bavaria Henry XII, called The Lion, decided that the bishops of Freising no longer needed their salt revenue. The gabelle–a French salt tax–was enacted in 1286 and maintained until 1790. Because of the gabelles, common salt was of such a high value that it caused mass population shifts and exodus, attracted invaders and caused wars.
In the second half of the 19th century its price finally became more reasonable. The main reason for this was that it finally became possible to gain it by mining instead from the evaporation of seawater, as mining is the cheaper of the two processes. However, unrefined rock salt lacks many of the trace elements normally found in table salt, making it a poor substitute as an exclusive salt source. The deleterious health effects of the exclusive use of rock salt are similar to the effects of the total lack of salt in one's diet. Today salt is universally accessible, relatively cheap and iodized.
Forms of edible salt
Main article: Sea salt
Some assert that unrefined sea salt is healthier or more 'natural' than refined salts. There are concerns, however, that raw sea or rock salts may not contain sufficient iodine salts to prevent iodine deficiency diseases like goitre.
Refined salt, that is nowadays most widely used, is mainly sodium chloride. Only about 7% of the refined salt is used as a food additive. The majority is sold for industrial use, from manufacturing pulp and paper to setting dyes in textiles and fabric, to producing soaps and detergents, and has great commercial value.
The manufacture and use of salt is one of the oldest chemical industries. Salt is also obtained by evaporation of seawater, 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 edible salt. These rock salt deposits were formed by the evaporation of ancient salt lakes. These deposits 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 precipitation most impurities (largely magnesium and calcium salts). Multiple stages of evaporation are then used to collect pure sodium chloride crystals, which are kiln-dried.
Anticaking agents (and potassium iodide, for iodized salt) are generally added at this point. These agents are hygroscopic chemicals which absorb humidity, keeping the salt crystals from sticking together. Some anticaking agents used are tricalcium phosphate, calcium or magnesium carbonates, fatty acid salts, magnesium oxide, silicon dioxide, sodium alumino-silicate, and alumino-calcium silicate. Concerns have been raised regarding the possible toxic effects of aluminum in the latter two compounds, however both the European Union and the United States FDA permit their use in regulated quantities.
The refined salt is then ready for packing and commercial distribution.
Table salt is refined salt, containing nearly pure (95% or greater) sodium chloride. It usually contains substances that make it free flowing (anticaking agents). Table salt is also often iodized—a small amount of potassium iodide is added as a dietary supplement. Table salt is mainly employed in cooking and as a table condiment. Iodized table salt has essentially eliminated 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 goiter, cretinism in children, and myxedema in adults.
Sodium is one of the primary electrolytes in the body. Too much or too little salt in the diet can lead to an electrolyte disturbance, which can cause severe, even fatal neurological problems. Excessive consumption of sodium has also been linked to high blood pressure.
Salt substitutes (with a taste similar to regular table salt) are available for individuals who wish to restrict their sodium intake. These substitutes contain mostly potassium chloride.
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