How Salt Works


Shannon Loitz gives her mother, Cheryl, a taste from the Bonneville Salt Flats in Utah. See more salt pictures.
Shannon Loitz gives her mother, Cheryl, a taste from the Bonneville Salt Flats in Utah. See more salt pictures.
George Frey/AFP/Getty Images

Salt is salt, right? When you go to the grocery store to replenish your supply, you probably expect to see just a few varieties, like iodized salt (what most of us use as "table salt") and kosher salt (a coarse salt popular with chefs). But you might also find things like "sel gris" and "fleur de sel." Some gourmets claim that these salts taste different from iodized salt and give additional flavor to foods seasoned with them.

Even if you try not to use much salt, it's almost impossible to avoid it. There are five tastes that all people are able to experience -- bitter, sweet, sour, salty and umami (meaning "delicious and savory taste" in Japanese). Only "salty" is directly related to a substance that we need to consume in order for our bodies to function correctly. Because of this need, humans and animals have a built-in taste for salt.

Salt Image Gallery

All salt contains two basic elements: sodium and chlorine. Sodium (chemical symbol Na) is a silvery-white metal that reacts violently when mixed with water and oxidizes in air. Chlorine (chemical symbol Cl) is greenish-yellow and exists as a gas at room temperature. Because both elements are so volatile, they're found in nature as part of compounds like sodium chloride (NaCl), which forms the mineral halite. Sodium chloride is about 60 percent chlorine and 40 percent sodium [source: Salt Institute]. Although sodium is volatile and chlorine is toxic, together as sodium chloride they're integral to life. Sodium chloride molecules are cubical. The large chloride ions are closely packed together, with smaller sodium ions filling in the spaces between them.

Not only do we need to consume salt, we also need it for a variety of nonfood uses. But if it's so important, why do health organizations recommend that we closely watch our intake? Apparently, there can be too much of a good thing. In this article, we'll examine exactly how salt works in the human body. We'll look at how much salt is too much and what happens when we overload on it or get too little of it. We'll also take a closer look at the many varieties of salt and how it's mined. Finally, we'll look at salt's place in history.

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Human Salt Consumption

George Frey/AFP/Getty Images                              Sylvia Frost floats on the Great Salt Lake in Utah, which is five to eight times saltier than the ocean.
George Frey/AFP/Getty Images Sylvia Frost floats on the Great Salt Lake in Utah, which is five to eight times saltier than the ocean.
George Frey/AFP/Getty Images

The sodium and chlorine in salt are electrolytes, minerals that conduct electricity in our fluids and tissues. The other main electrolytes are potassium, calcium and magnesium. Our kidneys maintain the balance of electrolytes and water by regulating the fluids that we take in and pass out of our bodies. If this balance is disturbed, our muscles, nerves and organs won't function correctly because the cells can't generate muscle contractions and nerve impulses.

Too little salt, or hyponatremia, is one of the most common electrolyte disturbances. You can lose sodium when you sweat or urinate excessively, experience severe vomiting or diarrhea, or when you drink a lot of water (which is why sports drinks contain electrolytes). Taking diuretics, which make the body excrete excess water, can also cause you to lose too much sodium. Ultimately, hyponatremia can lead to brain swelling and death. If you have very strong cravings for salt, you may be dehydrated or lacking one of the minerals in table salt. But an extreme salt craving can be a symptom of Addison's disease (a hormonal disorder) or Barrter's syndrome (a rare kidney disorder).

If you have too much sodium in your body, you might get very thirsty and urinate more to get rid of the excess. You probably hear about too much sodium, or hypernatremia, much more often than you hear about hyponatremia. But sometimes your kidneys can't eliminate all of the excess. When this happens, your blood volume can increase (because sodium holds in water), which in turn can make your heart pump harder. Because of this, some doctors have treated chronic fatigue syndrome by increasing the patient's sodium intake.

The National Heart, Blood and Lung Institute recommends that most people consume no more than 2.4 grams of sodium (the equivalent of about one teaspoon) per day [source: NHBLI]. We probably don't need more than half a gram per day to maintain the proper electrolyte balance [source: New York Times]. Many people eat several times that much.

Excess salt intake has been linked to many different medical conditions, but the links are often controversial. For example, many doctors and researchers claim that a low-sodium diet can help regulate blood pressure (because excess sodium can increase blood pressure). But others believe that reduced sodium doesn't have a significant effect on blood pressure. Too much salt has also been thought to cause heartburn and increase the risk of osteoporosis, ulcers and gastric cancer, but these links are somewhat controversial as well.

­­Regardless of the latest medical advice about salt intake, it's probably a good idea to pay attention to how much salt you're eating. Fast food and prepackaged convenience foods (like frozen dinners or canned soup) have a lot of sodium because salt helps preserve food by drawing out moisture and keeping out bacteria. So, if you eat a lot of fast food, you may be eating more salt than you think. But what type of salt is it? In the next section, we'll learn about the many different kinds of salt.­­

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Table Salt and Sea Salt

Table salt is the most commonly used salt.
Table salt is the most commonly used salt.
Duncan Smith/Photodisc/Getty Images

The different varieties of salt available for cooking can be dizzying, but all of them fall into four basic types: table salt, sea salt, kosher salt and rock salt. The first three types are food-grade salt and are required by the FDA to contain at least 97.5 percent sodium chloride. The other 2.5 percent is trace minerals, chemicals from processing or anti-caking agents.

Table Salt

Table salt is either iodized or noniodized. Iodine was first added to salt in the mid-1920s to combat an epidemic of hyperthyroidism, an enlargement of the thyroid gland caused by hormonal irregularities due to lack of iodine. Children without sufficient iodine intake can also experience stunted physical and mental growth. Few people suffer from iodine deficiency in North America, although it is still a problem around the world. In some areas, fluoride and folic acid are also common salt additives.

Table salt is the most commonly used salt. It is processed to remove impurities and contains nonclumping agents like calcium phosphate. Because it has a fine texture, table salt is easy to measure and mixes evenly.

Sea Salt

Sea salt is generally more expensive than table salt because of how it's harvested. "Fleur de sel" (French for "flower of salt"), for example, is scraped by hand from the surface of evaporation ponds. Some sea salts are not as heavily processed as table salt, so they retain trace minerals that are usually removed in the refining process. Sea salt can be coarse, fine or flaky. It can be white, pink, black, gray or a combination of colors, depending on where it comes from and which minerals it contains.

Some pink salts, such as the salt harvested in the Himalayas, get their color from calcium, magnesium, potassium, copper and iron, Others contain carotene from salt-tolerant algae and are more peach-colored. Reddish-pink salts, such as Hawaiian alaea salt, have iron oxide added in the form of volcanic clay.

Black salt is often really more of a dark pinkish-gray color. One Indian variety contains sulfurous compounds, iron and other trace minerals and has a strong, sulfuric taste. Hawaiian black lava salt is darker and contains traces of charcoal and lava.

The color of gray salt comes from trace minerals or from the clay where it is harvested, such as the damp, unrefined "sel gris" harvested on the coast of France. Smoked salt is also grayish and is a fairly new offering among the gourmet varieties of salt. It is smoked over wood fires and gives a smoky flavor to dishes seasoned with it.

Some gourmands argue that the higher amounts of trace minerals can give sea salts a unique, earthy flavor. Others say that the taste is about the same but that their different colors and textures can add a lot to presentation. In general, sea salts are used to top or "finish" a dish rather than during cooking.

On the next page we'll learn about kosher and rock salts.­

Kosher Salt and Rock Salt

Gali Tibbon/AFP/Getty Images                              Salt deposits on the Dead Sea shoreline show its decreasing water level.
Gali Tibbon/AFP/Getty Images Salt deposits on the Dead Sea shoreline show its decreasing water level.
Gali Tibbon/AFP/Getty Images

Kosher salt

Kosher salt is used to make meats kosher by quickly drawing out the blood. Many chefs prefer to use kosher salt. Its coarse texture makes it easy to pick up and sprinkle on food during or after cooking. However, it doesn't dissolve as quickly as table salt, so it's better to use a finer salt when baking. When replacing table salt with kosher salt in a recipe, you usually need to double the amount because the larger kosher salt crystals take up more space.

Kosher salt is not iodized. Some claim that this makes it better to cook with -- iodine makes table salt taste slightly metallic. Because we can usually get iodine from many sources other than the salt that we cook with, there's no reason to worry about using noniodized salt.

­­Rock salt

Rock salt is a large-grained, unrefined salt that usually contains inedible impurities. It does have one use in cooking: Homemade ice cream recipes often instruct you to sprinkle rock salt on the ice surrounding the cylinder filled with the ice cream mixture. Salt makes ice melt faster, and the resulting salt and water mix freezes at a lower temperature than ice alone. This makes the ice cream freeze faster. Rock salt is also sprinkled on icy roadways and sidewalks to melt the ice.

We'll learn where all of these different types of salt come from in the next section.

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Salt Mining

Andy Satiriou/Photodisc/Getty Images                              A salt-refining plant near Murcia, Spain
Andy Satiriou/Photodisc/Getty Images A salt-refining plant near Murcia, Spain
Andy Satiriou/Photodisc/Getty Images

In 2006, more than 200 million tons of salt were produced in the world. China is the largest producer, with 48 million tons, followed closely by the United States, with 46 million tons [source: Salt Institute]. Salt is generally produced one of three ways: deep-shaft mining, solution mining or solar evaporation.

Deep-shaft 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 thousands 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.

In solution mining, wells are erected over salt beds or domes (deposits of salt forced up out of the earth by tectonic pressure) and water is injected to dissolve the salt. Then the salt solution, or brine, is pumped out and taken to a plant for evaporation. At the plant, the brine is treated to remove minerals and pumped into vacuum pans, sealed containers in which the brine is boiled and then evaporated until the salt is left behind. Then it is dried and refined. Depending on the type of salt it will be, iodine and an anti-clumping agent are added to the salt. Most table salt is produced this way.

When solution mines are located near chemical plants, they are called brine wells, and the salt is used for chemical production. After the salt is removed from a salt mine, the empty room often stores other substances, like natural gas or industrial wastes.

Salt is harvested through solar evaporation from seawater or salt lakes. Wind and the sun evaporate the water from shallow pools, leaving the salt behind. It is usually harvested once a year when the salt reaches a specific thickness. After harvest, the salt is washed, drained, cleaned and refined. This is the purest way to harvest salt, often resulting in nearly 100 percent sodium chloride. Only areas with low annual rainfall and high evaporation rates -- Mediterranean countries and Australia, for example -- can have successful solar evaporation plants. Usually machines perform this harvest, but in some areas it is still done by hand.

Next, we'll look at the history of salt and learn about some of its cultural significance.

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History of Salt

Sumo wrestler Chiyotaiki purifies the ring with salt at the Grand Sumo Championship.
Sumo wrestler Chiyotaiki purifies the ring with salt at the Grand Sumo Championship.
Donald Miralle/Getty Images

Prior to industrialization, it was extremely expensive and labor-intensive to harvest the mass quantities of salt necessary for food preservation and seasoning. This made salt an extremely valuable commodity. Entire economies were based on salt production and trade.

In the Iron Age, the British evaporated salt by boiling seawater or brine from salt spri­ngs in small clay pots over open fires. Roman salt-making entailed boiling the seawater in large lead-lined pans. Salt was used as currency in ancient Rome, and the roots of the words "soldier" and "salary" can be traced to Latin words related to giving or receiving salt. During the Middle Ages, salt was transported along roads built especially for that purpose. One of the most famous of these roads is the Old Salt Route in Northern Germany, which ran from the salt mines to shipping ports.

Salt taxes and monopolies have led to wars and protests everywhere from China to parts of Africa. Anger over the salt tax was one of the causes of the French Revolution. In colonial India, only the British government could produce and profit from the salt production conducted by Indians living on the coast. Gandhi chose to protest this monopoly in March 1930 and marched for 23 days with his followers. When he arrived on the coast, Gandhi violated the law by boiling a chunk of salty mud. This march became known as the Salt March to Dandi, or the Salt Satyagraha. People across India began making their own salt in protest, and the march became an important milestone in the struggle for Indian independence.

Salt production also played a significant role in early America. The Massachusetts Bay Colony held the first patent to produce salt in the colonies and continued to produce it for the next 200 years. The Erie Canal was opened primarily to make salt transportation easier, and during the Civil War, the Union captured significant Confederate saltworks and created a temporary salt shortage in the Confederate states. It continues to be important to the economies of many states, including Ohio, Louisiana and Texas.

Aside from economics, salt also has cultural and religious significance. It has long been used in Shintoism to purify things, and Buddhists use salt to repel evil. In Judeo-Christian traditions, salt was used to purify people and objects, as an offering, and to seal covenants. There are numerous references to salt in the Old and New Testaments of the Bible. One of the most famous is Lot's wife, who was turned into a pillar of salt in Genesis after disobeying God's command. A rock-salt pillar that stands today on Mount Sodom is known as "Lot's Wife."

There are lots of sayings related to the use of salt. It was often traded for slaves, which is the origin of the expression "not worth his salt." Someone who is the "salt of the earth" is a dependable, unpretentious person. "Salting the earth," on the other hand, refers to an ancient military practice of plowing fields with salt so that no crops could be grown.

For lots more information on salt, check out the links on the next page.

Related HowStuffWorks Articles

More Great Links

Sources

  • Greely, Alexandra. "A Pinch of Controversy Shakes Up Dietary Salt." FDA Consumer Magazine, Nov-Dec 1997.
  • http://www.fda.gov/fdac/features/1997/797_salt.html
  • Kurlansky, Mark. "Salt: A History." Walker & Company, 2002.
  • "A Natural History of Salt." Ventura County Star, July 21, 2002
  • Parrish, Marlene."Sea Salt Adds Wave of Extra Zip and Crunch." Pittsburgh Post Gazette, August 28, 2003. http://www.post-gazette.com/food/20030828salttasting0828fnp3.asp
  • "Prevention: Guide to Lower Blood Pressure." National Health Library. http://www.nhlbi.nih.gov/hbp/prevent/prevent.htm
  • "Problems With Electrolyte Balance." The Merck Manual of Health and Aging. http://www.merck.com/pubs/mmanual_ha/sec3/ch18/ch18d.html
  • The Salt Institute. http://www.saltinstitute.org
  • The Salt Manufacturers Association. http://www.saltsense.co.uk/index.htm
  • "Salt Raises 'Stomach Cancer' Risk." BBC News, January 7, 2004. http://news.bbc.co.uk/1/hi/health/3370141.stm
  • "Sodium -- Are you getting too much?" Mayo Clinic. http://www.mayoclinic.com/health/sodium/NU00284
  • "Sodium: Principal Compounds." Encyclopedia Brittanica. http://www.britannica.com/eb/article-6744/sodium
  • Solution Mining Research Institute. http://www.solutionmining.org/
  • Taubes, Gary. "The (Political) Science of Salt."Science Magazine, August 14,­ 1998. http://www.sciencemag.org/cgi/content/full/281/5379/898?ijkey=ATm56Jl8nBVYU
  • ­Zuger, Abigail. "With Dietary Salt, What 'Everyone Knows' Is in Dispute." New York Times, September 1, 2001. http://www.nytimes.com/2001/01/09/health/09SALT.html?ex=1194321600&en=260217115494b8a0&ei=5070