Answers to some common questions. For more, see our explanations about salt , about the myriad uses of salt , about how salt is produced and some public policy questions about how we make and use this valuable material. Explore and learn about how salt affects blood pressure, the differences between rock salt, iodized salt an kosher salt, and more.
Want still more? See our collected articles and references .
ONE-PAGE FACT SHEETS provide concise, reliable research and data at your fingertips on food salt, road salt, and water softening. These fact sheets in PDF format print beautifully and are handy aids for sales staff, journalists, public officials researchers, students, and anyone interested in salt.
Sodium chloride or common salt is the chemical compound NaCl, composed of the elements sodium and chloride. Salt occurs naturally in many parts of the world as the mineral halite and as mixed evaporites in salt lakes. Seawater has lots of salt; it contains an average of 2.7% (by weight) NaCl, or 26 million metric tons per cubic kilometer, an inexhaustible supply (note: seawater also contains other dissolved solids; salt represents about 77% of the Total Dissolved Solids). Underground salt deposits are found in both bedded sedimentary layers and domal deposits . Deposits have been found to have encapsulated ancient microorganisms including bacteria. Some salt is on the surface, the dried-up residue of ancient seas like the famed Bonneville Salt Flats in Utah. Salt even arrives on earth from outer space in meteors and its presence on the planet Mars makes scientists think life may exist there (in fact, scientists speculate that salt-loving bacteria live in underground water on Mars -- as they have survived in suspended animation for 250 million years in Texas ). Conversely, surface salt depositions and man-made saltworks can be seen from space. In ocean coastal areas, saltwater can "intrude" on underground freshwater supplies , complicating the lives of those who provide our drinking water supplies.
Sodium chloride crystals are cubic in form. Table salt consists of tiny cubes tightly bound together through ionic bonding of the sodium and chloride ions. The salt crystal is often used as an example of crystalline structure. Many online science pages offer instruction on growing salt crystals . Other graphics of salt crystals are also available online. Different types of crystal have different uses, as for food . Read more... (pdf 81.69 kB)
There's a huge amount of salt in the world -- about 3.5% of the weight of the world's oceans plus massive underground (and underwater) deposits. <more >
History of Salt
Most people probably think of salt as simply that white granular food seasoning found in a salt shaker on virtually every dining table.
It is that, surely, but it is far more. Salt is an essential element in the diet of not only humans but of animals in general. It is one of the most effective and most widely used of all food preservatives (and used to preserve Egyptian mummies as well). Its industrial, medical and other uses are almost without number. In fact, salt has great current as well as historical interest , and is even the subject of humorous cartoons , music , "art " and poetry . Read more… (pdf 182.85 kB)
Consumer Tips for Salt Use
Besides making foods delicious , it's believed there are more than 14,000 uses of salt, and our grandmothers were probably familiar with most of them. Many of these uses were for simple things around the home before the advent of modern chemicals and cleaners. Many "old" uses are still valid today and a lot cheaper than using more sophisticated products. Read more... (pdf 50.70 kB)
In 2008, world salt production amounted to about 260 million tons. Further details on specific country production, including the U.S. can be found here .
The salt industry
Every day, each of the earth's 5.9 billion inhabitants uses salt. Annual salt production has increased over the past century from 10 million tons to over 200 million tons today. Nearly 100 nations have salt producing facilities ranging from primitive solar evaporation to advanced, multi-stage evaporation in salt refineries.
The U.S. salt industry began in 1614 when the first non-native solar saltworks was established by the Jamestown colonists on Smith's Island, VA. The U.S. is the world's second largest salt producer, producing 46 million tons a year, nearly half of that in the form of brines produced by captive brine wells supplying U.S. chloralkali chemical companies in such states as Michigan, Texas and West Virginia . The remaining is "dry salt" produced using three basic technologies : solar evaporation of seawater or saline lakewater, solution mining and vacuum pan evaporation and conventional deep-shaft (rock salt) mining . Currently, the U.S. salt industry operates 48 salt production plants with major production sites in Louisiana, Ohio, New York, Kansas, Michigan, Utah, Texas and California. All major U.S. salt producers are members of the Salt Institute . Online maps show production and distribution for the three largest companies, Cargill , Compass Minerals and Morton Salt . U.S. salt production is also tracked by the U.S. Geological Survey . Michigan State University has a nice review of saltmaking in Michigan .
Solar Salt Production
Solar salt is produced by the action of sun and wind on seawater ( 1 2 ) or natural brine in lakes; both temperature and salinity are important. The water evaporates in successive ponds until the brine is fully concentrated and salt crystallizes on the floor of the crystallizing ponds. Solar salt plants must be located in areas of low rainfall and high evaporation rates, and where suitable low-cost is available. In the Mediterranean, for example, saltworks succeed because evaporation exceeds rainfall by a factor of 3:1; that advantage is even greater in Australia where it can reach 15:1 .
Seawater contains about 3.5% (by weight) dissolved minerals. Sodium chloride is 77% of that amount, or about 2.7% of seawater. The other 0.8% consists chiefly of calcium, magnesium and sulfate ions. As seawater evaporates, its volume decreases and the concentration of sodium chloride in the resulting brine increases. Thus, saltworks generally extract as sodium chloride a bit over 2% of the weight of the influent seawater. This means that solar saltworks are often quite extensive in area. Often, the concentrating ponds will have distinct coloration, a pink or red , depending on the salt concentration and what species of plants and animals find it habitable. Salt crystals begin to form when the brine concentration reaches 25.8 % sodium chloride (NaCl). As evaporation proceeds, a layer of salt builds up on the earthen crystallizer floors to a thickness of 10 to 25 cm (4-10 in). Sometimes, a layer of salt remains in the crystallizers as "salt floors" to provide support for "harvesting" equipment and to lessen the chance of clay or soil contamination of the salt. A modern, properly operated solar salt plant can produce salt that is more than 99.7 % NaCl (dry basis). In the Dead Sea, salt producers have to contend with "salt mushrooms ."
Solution mining of salt is the extraction of salt using fresh and recycled water injected through a well (or wells) into an underground salt bed or salt dome , usually between 150 and 1,500 meters (500 to 5000 feet) deep. Dissolution of the salt forms a void or cavern in the salt deposit. Salt brine is withdrawn from the cavern and transported by pipeline to an onsite evaporating plant to make dry salt, or to a chemical processing plant for chloralkali or other chemical production. Read more... (pdf 70.06 kB)
Table salt is typical of the fine, granulated-evaporated salt produced in vacuum pan evaporators. Virtually all food grade salt sold or used in the United States is produced by vacuum evaporation of brine. Prior to mechanical evaporation, the brine may be treated to remove minerals that can cause scaling in the evaporators and adversely affect salt purity. Water is removed from brine using steam or electric-powered multiple-effect evaporators. Multiple-effect systems typically contain three or four forced-circulation evaporating vessels connected together in a series. Read more... (pdf 55.29 kB)
Rock salt mining is much like mining for any other mineral. Typically, the salt exists as deposits in ancient underground seabeds, which became buried through tectonic changes over millions of years. Many salt mines use the "room and pillar" system of mining. Shafts are sunk down to the floor of the mine, and rooms are carefully constructed by drilling, cutting and blasting between the shafts, creating a checkerboard pattern. After the salt is removed and crushed, a conveyor belt hauls it to the surface. Most salt produced this way is used as rock salt. Read more... (pdf 81.95 kB)
Highway Deicing and Anti-icing for Safety and Mobility
Winter highway maintenance is a major market for salt, although that market is sometimes geographically distant from the production site and hard to resupply during the middle of winter, particularly after waterways freeze. Highways play a vital role in assuring personal and commercial mobility and the productivity of the overall economy ( see our (vnd.rn-realmedia 3.78 MB) 3.77 MB RealMedia video (vnd.rn-realmedia 4.27 MB) ) as evidenced by the success of the U.S. Interstate Highway Program . Salt is used to keep highways safe and passable. ( see our 4.26 MB (pdf 158.58 kB) RealMedia video (pdf 1.01 MB) ).
Research indicates that using salt, snowfighting crews can reduce accidents sharply. A study by the Marquette University Department of Civil and Environmental Engineering documented injury accident reduction of 88.3% , paralleling findings of an earlier German study. The Salt Institute has published short summaries of the results of two important studies by Marquette University on the safety impacts of winter maintenance: The Public's Right to Wintertime Traffic Safety (pdf 729.29 kB) and Cost Effective Wintertime Mobility and Safety: We Deserve It, We Can Afford It (pdf 822.12 kB) . Both are available in English as a free download and the first also in French, Le Droit du public à des routes s ûres en hiver (pdf 500.75 kB) .
When salt usage is properly managed, it has little impact on the environment (see our publication Highway Salt and Our Environment - free downloads in English (pdf 152.98 kB) and French (pdf 94.48 kB) ). Read more... (pdf 60.95 kB)
Salt: Leading Chemical Feedstock
Salt is the feedstock of the chlor-alkali industy (see these great graphics illustrating the "chlorine tree" ( 1 2 ) and used for the manufacture of chlorine ( 1 2 ) caustic soda and many other industrial and inorganic chemicals, and allied products. Chemical production is a major market for salt. During 1996, the most recent year for which data are available, 22.4 million metric tons of salt (NaCl) were consumed by the chemical industry. The chemical industry is the largest single user of salt (dry salt and salt in brine) in the United States, representing about 42% of total salt consumption during 1996. More than 88% of the salt used for chemical manufacture was salt in brine, which is produced by solution mining underground halite deposits. This "captive brine" is produced by chemical companies solely for use in making their products. The remaining 12% (2.6 million metric tons) was "dry" salt produced by rock salt mining, solar evaporation, and mechanical evaporation of solution-mined brine.
A salt bridge is an important component of an electrochemical cell. Electrolysis ( 1 2 3 4 5 ) is used to break sodium chloride into its component ions and to make chlorine ( 1 2 ), sodium hydroxide or caustic soda , sodium chlorite and soda chlorate , for example. Chlorine (Cl2) and caustic soda (NaOH), also known as sodium hydroxide are the two primary chemical products made from salt. Ninety-five percent of salt used by the chemical industry is in the manufacture of chorine and caustic soda. Chlorine has many uses , including keeping drinking water safe . Gaseous chlorine (Cl2) and caustic soda (NaOH) are produced when an electric current passes through saturated salt brine. Chlorine is an effective disinfectant and bleach. Downstream, vinyl chloride and polyvinyl chloride (PVC) and their derivatives are produced from chlorine. Caustic soda is used in pulp processing, and to make cellulose chemicals and their derivatives. Sodium chlorite is used in the textile industry . Other chemicals manufactured from salt are metallic sodium and sodium chlorate. Until 1986, salt was used to produce synthetic soda ash (NaCO3) in the U.S. by the Solvay process. Soda ash is now obtained naturally from trona mines.
Due to security concerns with the transportation of chlorine in tanker trucks and rail cars, including chemical terrorism (aka "toxic trains "), some chlorine users are exploring the use of on-site chlorinators ( 1 2 3 )
For further information you may wish to visit the Chemical Industry Home Page , the Chlorine Chemistry Council (don't miss their Science Center ), Chlorine Institute , EuroChlor and Canadian Chlorine Coordinating Committee . European chemical production can be tracked online. Note our disclaimer .
Human dietary consumption is a major market for salt.
Salt serves many purposes . Salt is the world's oldest known food additive and no decent kitchen would be without salt . People use many types of sodium chloride in food processing , cooking (see pg 640 ff) or at the table -- at home or in restaurants . Each makes its unique contribution . Besides contributing its own basic "salty" taste, salt has many benefits . It brings out natural flavors and makes foods acceptable, protects food safety by retarding the growth of spoilage microorganisms, gives proper texture to processed foods, serves as a control agent to regulate the rate of fermentation in food processing strengthens gluten in bread, provides the color, aroma and appearance consumers expect and is used to create the gel necessary to process meats and sausages. As a result, more heavily processed foods usually contain more sodium and salt.
Read more and get links to recipes... (pdf 67.17 kB)
One level U.S. teaspoonful of granulated evaporated salt contains approximately 6,200 mg sodium chloride, or approximately 2,400 mg sodium.
The density of granulated evaporated salt varies depending on crystal size, structure, gradation, and degree of compaction. The reported range of densities is 1,200-1,300 g/L. Michaels (1991)[i] uses 1,300-1,315 g/L for Hygrade and Fine salt from Sifto’s Goderich evap plant. Niman (1979)[ii] , and Bandy (1989)[iii] use 1,250 g/L for granulated evaporated salt (loose bulk density = 800 cc/1,000 g). Niman (1979) gives the density of Alberger as 624 - 750 g/L depending on gradation. Akzo Salt Inc. (1992)[iv] gives the density of General Purpose granulated evaporated salt as 77 lbs/ft3 (1,233 g/L), and of Granulated Iodized as 75 lb/ft3 (1,201 g/L). Akzo Salt Inc. gives densities for Alberger Natural Flake Salt as 39-60 lb/ft3 (625-960 g/L), and Tru-Flake Compacted Flake Salt as 59-70 lb/ft3 (945-1,121 g/L) depending on gradation. The coarse products are generally of lower density.
Assuming evaporated granulated salt with a density of 1,250 g/L and 1 U.S. teaspoon = 4/93 mL (1 metric teaspoon = 5.0 mL):
Salt (NaCl): 1,250 g/L = 1,250 mg/mL x 4.93 mL/U.S. tsp. = 6,162 mg/U.S. tsp.
Sodium: 6,162 mg/U.S. tsp. x 0.39337% Na = 2,424 mg/U.S. tsp.
A simple summary is that about six grams of salt makes a level teaspoonful and just under 2.4 grams is sodium. This is exactly correct for salt with a density of 1,217 g/L. Based on a salt density of 1,250 g/L, one level teaspoon contains approximately 6,200 mg NaCl and approximately 2,400 mg sodium.
[i] Michaels, Peter G. 1991. Sifto Canada, Inc. Personal correspondence
[ii] Niman, Clarence E. 1979. Salt is not "just salt"-considerable differences exist. Food Engineering. September.
[iii] Bandy, Jack. 1989. Technical Spotlight, Vol. 90-9. Cargill, Incorporated. February.
[iv] Akzo Salt Inc. 1992. Chemical Week. Pp 455-458. October.
Salt and Cardiovascular Health
For 4,000 years, we have known that salt intakes can affect blood pressure through signals to the muscles of blood vessels trying to maintain blood pressure within a proper range. We know that a minority of the population can lower blood pressure by restricting dietary salt. And we know that elevated blood pressure, "hypertension," is a well-documented marker or "risk factor" for cardiovascular events like heart attacks and strokes, however, seleted risk factors do not necessarily reflect actual health outcomes.
One of salt's major functions is to regulate blood volume and pressure including the flexibility of the blood vessels. The human heart is a big pump. When it contracts, it forces blood through the arteries of the circulatory system; that pressure is "systolic," the "top" number. Between heartbeats, the heart relaxes. Pressure measured between heartbeats is "diastolic," the "bottom" number. When blood volume increases or the blood vessel walls don't expand enough, blood pressure increases. Normal blood pressure is less than 130/85 according to the National Heart, Lung and Blood Institute. In a population, blood pressures are a good indicator of the incidence of cardiovascular events like heart attacks and strokes.
We know that for some salt-sensitive individuals, reducing salt intake will reduce blood pressure, but will it improve their overall health outcomes? Most published medical studies indicate this is not the case. Read more… (pdf 86.40 kB)
Most doctors believe that restriction of salt intake for the normotensive population is not recommended at present, because of insufficient evidence demonstrating that this would lead to a reduced incidence of hypertension. To avoid excessive intake of salt, people should be counselled to choose foods low in salt (e.g., fresh fruits and vegetables), to avoid foods high in salt (e.g., pre-prepared foods), to refrain from adding salt at the table and minimize the amount of salt used in cooking, and to increase awareness of the salt content of food choices in restaurants. Read more... (pdf 198.08 kB)
A repeat Cochrane Collaboration review of the intensive interventions of salt reduction were found to be unsuited to primary care or population prevention programmes, and provided only minimal reductions in blood pressure during long-term trials. Further evaluations were needed to assess effects on morbidity and mortality outcomes for populations as a whole and for patients with elevated blood pressure. Read more... (pdf 34.54 kB)
We know that we have to keep our nutrients, including salt, in balance to maintain good health. If not, we can be subject to a number of negative conditions, including chronic fatigue syndrome. Read more... (pdf 34.54 kB)
There is no question that any heightened physical activity results in excessive loss of salt which has to be replenished. Hyponatremia means a low concentration of sodium in the blood. When it occurs in athletes, it usually happens during long or ultra-distance races in the heat but may occur anytime. The longer the event, the greater the risk of hyponatremia. So athletes definitely require extra salt . Read more... (pdf 61.55 kB)
Iodine Deficiency Diseases, including mental retardation, goiter and cretinism result from an insufficient level of iodine in the diet. For almost a century, iodized salt has proven to be the most effective means of providing populations around the world with consistent levels of iodine capable of eliminating these terrible diseases. This is why the World health Organization has considered salt iodization to be one of the 20th century's greatest public health triumphs. Read more...
Many chefs prefer kosher salt in cooking certain dishes, usually as a topping, to add special crunch or taste to food. Kosher salt is made by similar evaporation processes as cubic table salt, both plain and iodized. However some processes allow their crystals to growth at normal atmospheric pressure which makes a different shaped and larger crystal possible. Read more.... (pdf 25.61 kB)