Salt is one of those things that is so ordinary that we hardly notice it. There is probably a salt shaker somewhere in your kitchen right now, and you may use salt without giving it a second thought.
Yet salt is far more remarkable than its humble appearance suggests.
It has been essential to human life from the beginning. It is found in oceans, underground rocks, salt lakes, soils, plants, animals, and even our own bodies. It has been used to preserve food, make medicines, tan leather, manufacture chemicals, melt ice, soften water, and flavor nearly every kind of cuisine.
For thousands of years, salt was valuable enough to influence trade, exploration, wars, settlements, and even the locations of cities.
And there is an especially fascinating question hiding inside your question:
If salt is necessary for life, why can't we drink the ocean?
The answer involves the delicate balance of water and salt inside living things.
What exactly is salt?
The salt we normally mean when we talk about cooking is sodium chloride, commonly written as NaCl.
It is made from two elements:
Sodium (Na)
Chlorine (Cl)
Sodium is a soft, highly reactive metal, while chlorine is a poisonous greenish-yellow gas. Yet when they combine chemically, they produce the familiar white crystals we call salt.
That is a wonderful example of how chemistry works: two elements with very different properties can combine to make something entirely different from either of them.
Table salt is approximately 40% sodium and 60% chloride by weight. (CDC)
But there is an important distinction:
Salt and sodium are not exactly the same thing.
Sodium is one component of salt. When nutrition labels tell you how much "sodium" is in a food, they are referring specifically to the sodium portion, not the entire salt molecule.
Where is salt found?
Salt is practically everywhere.
The oceans
The greatest visible supply is the world's oceans.
Ordinary seawater contains about 35 grams of dissolved salts per kilogram of seawater, or roughly 3.5%. (National Ocean Service)
And the ocean isn't simply a gigantic tank filled with table salt.
Seawater contains many dissolved substances, including sodium chloride, magnesium salts, calcium compounds and other minerals. Sodium and chloride together account for about 85% of the dissolved ions in seawater. (National Ocean Service)
Underground
There are enormous deposits of salt buried beneath the Earth.
Millions of years ago, portions of ancient seas became isolated. Their water evaporated, leaving salt behind. Over immense periods of time, these deposits were buried beneath layers of sediment.
Some deposits are so large that they form underground salt domes.
This is one of the principal sources of the salt used by humans today.
Salt lakes
There are also lakes whose water contains enormous quantities of dissolved salt.
The famous Great Salt Lake in Utah is an example. Other extraordinarily salty bodies of water include the Dead Sea.
In living things
Salt is also present inside plants, animals and people.
Our blood and other body fluids contain sodium and chloride ions. They are essential to the proper functioning of cells, nerves and muscles.
So salt isn't merely something that sits on the dinner table.
A little bit of salt chemistry is taking place inside you every moment of your life.
How did the ocean become salty?
This is a wonderful story.
Rainwater isn't completely chemically pure. As rain falls through the atmosphere and reaches the ground, it can become slightly acidic. Over enormous periods of time, rainwater slowly wears away rocks.
The water dissolves tiny quantities of minerals from those rocks.
Streams and rivers then carry those dissolved substances toward the sea.
The ocean therefore acts somewhat like an enormous collection basin.
Water continually evaporates from the ocean, but the dissolved salts generally remain behind. Over geological time, this helped make the oceans salty. Hydrothermal vents and underwater volcanic activity also contribute minerals to seawater. (National Ocean Service)
So when you look at a river flowing toward the ocean, you are looking at part of a gigantic natural mineral transportation system.
Was salt ever valuable?
Extremely valuable.
Today salt is inexpensive enough that we hardly think about its price. But for much of human history, salt could be a precious commodity.
The reason is simple:
People need salt, but naturally occurring concentrated salt isn't available everywhere.
Before refrigeration and modern food preservation, salt was especially important because it could help preserve meat, fish and other foods.
A community that possessed a dependable salt source could have an enormous advantage.
Salt became an important trade commodity in ancient civilizations, and salt routes developed across Europe, Asia and Africa.
The word salary is sometimes said to have come from Roman soldiers being paid in salt, but that popular story is more complicated than the saying suggests. There is a connection between the Latin word sal (salt) and several words associated with salt and payments, but there is no good evidence that Roman soldiers literally received their wages in salt.
Nevertheless, the underlying idea tells us something important:
People understood salt's value.
How is salt obtained?
There are several major methods.
1. Mining
Salt can be extracted from underground deposits much like other minerals.
Miners can remove solid salt from underground chambers.
2. Evaporating seawater
Saltwater can be placed in shallow ponds where sunlight and wind gradually evaporate the water.
Eventually, salt crystals remain.
This method has been used for thousands of years.
3. Solution mining
Water can be pumped underground into a salt deposit.
The salt dissolves into the water, creating a very salty solution called brine.
The brine is then pumped back to the surface and processed.
What are the different kinds of salt?
There are many varieties, and the differences can be surprisingly interesting.
Table salt
This is the familiar fine-grained salt found in many kitchens.
It is generally mined from underground deposits and processed to remove impurities and produce uniform crystals. Many brands of table salt are iodized, meaning iodine has been added. (Mayo Clinic)
Sea salt
Sea salt is produced by evaporating seawater.
Depending on how it is produced, it may retain small amounts of other minerals and have somewhat different textures and flavors.
Kosher salt
Kosher salt generally has larger, flatter or more irregular crystals than ordinary table salt.
It is popular among cooks because its texture makes it easy to pick up with the fingers and distribute over food.
Himalayan pink salt
This salt comes from underground salt deposits, particularly those associated with the Himalayan region. Its pinkish color comes from trace minerals.
It is attractive and popular, but it isn't a magical health food.
Fleur de sel
The name means "flower of salt" in French.
It consists of delicate crystals that form at the surface of certain salt ponds and are carefully collected.
It is considered a specialty finishing salt.
Pickling salt
This is a fine-grained salt formulated for pickling. It generally lacks additives that could make pickling liquid cloudy.
Rock salt
Rock salt consists of larger pieces of salt and is commonly used for purposes other than directly seasoning food.
One familiar use is helping melt ice.
Is sea salt better than regular salt in food?
This is one of those questions where advertising sometimes makes the answer more complicated than it needs to be.
For most people, sea salt isn't nutritionally superior to ordinary table salt.
Sea salt and table salt contain approximately comparable amounts of sodium by weight. Their principal differences are generally texture, flavor, crystal size and processing. (Mayo Clinic)
Sea salt may have tiny amounts of other minerals that contribute to its flavor or color, but these quantities generally aren't large enough to make sea salt a major nutritional source of minerals.
There is another important difference:
Iodine.
In the United States, ordinary table salt is commonly available in an iodized form.
Sea salt is usually not iodized unless the package specifically says it is.
The NIH notes that specialty salts such as sea salt, kosher salt and Himalayan salt usually contain little or no iodine. (ODS)
Iodine is necessary for normal thyroid function.
So I wouldn't say sea salt is "better."
I'd say:
Choose the salt you like for cooking, but if you rely on salt as a source of iodine, check the label to see whether it is iodized.
What does salt do inside the human body?
This is where salt becomes truly important.
Your body needs sodium.
Sodium helps regulate:
fluid balance
nerve impulses
muscle contraction
normal cellular function
Your nervous system couldn't work properly without carefully controlled concentrations of sodium and other electrolytes.
When a nerve cell sends an electrical signal, sodium ions are part of the process.
Your heart and muscles also depend on these carefully maintained chemical gradients.
So when we say "salt is necessary for life," that isn't an exaggeration.
What happens if a person doesn't get enough salt?
A person can develop low blood sodium, called hyponatremia, when the amount of sodium in the body becomes abnormally low.
This can happen for several different reasons, and it isn't simply a matter of "not eating enough salt."
For example, excessive water intake under certain circumstances can dilute sodium in the blood.
Some medical conditions and medications can also contribute.
Symptoms of significantly low blood sodium can include:
headache
nausea
confusion
weakness
muscle problems
seizures
in severe cases, loss of consciousness
That doesn't mean people should deliberately eat large amounts of salt.
In fact, the more common problem in the United States is too much sodium rather than too little. The CDC notes that excessive sodium intake can contribute to high blood pressure and increase the risk of heart disease and stroke. (CDC)
So salt is a perfect example of something that the body needs in the right amount.
Too little can be dangerous.
Too much can also be dangerous.
Why do some animals live in salt water instead of fresh water?
Now we get to one of the most fascinating parts of the question.
The answer is essentially:
They evolved to live there.
But their bodies have to solve a difficult chemical problem.
Imagine a fish swimming through seawater.
The water surrounding it contains a great deal of salt.
The fluids inside the fish contain considerably less salt.
Water naturally moves across biological membranes in response to differences in concentration. This creates a constant challenge called osmoregulation—the process of maintaining the proper balance of water and dissolved substances in the body. (NOAA Institutional Repository)
A marine fish therefore has specialized mechanisms to deal with the salt.
Its gills and kidneys play important roles in maintaining the correct internal balance.
What about freshwater fish?
They have almost the opposite problem.
Freshwater contains very little dissolved salt compared with the body fluids of a fish.
Water therefore tends to move into the fish.
A freshwater fish has to prevent itself from becoming excessively diluted.
It takes in salts through specialized mechanisms and produces large amounts of dilute urine to get rid of excess water. (NOAA Institutional Repository)
So a fish has to maintain an internal chemical environment that is different from the water around it.
That is an extraordinary piece of biology.
Some animals can live in both
There are animals that can tolerate considerable changes in salinity.
Some fish migrate between rivers and oceans.
Salmon are famous examples.
They hatch in freshwater, spend part of their lives in the ocean, and eventually return to freshwater to reproduce.
Their bodies undergo remarkable physiological changes to cope with the different environments.
Estuaries are especially interesting because they contain a mixture of fresh and salt water. These areas become important nurseries for many species. (NOAA Fisheries)
How do sea turtles get rid of salt?
Sea turtles have one of nature's most fascinating solutions.
They have special salt glands near their eyes.
These glands allow them to remove excess salt from their bodies.
The salty liquid comes out through openings near the eyes, which can make a sea turtle appear to be crying.
It isn't crying because it is sad.
It is essentially getting rid of salt.
This adaptation is particularly important because sea turtles swallow seawater while feeding. (Smithsonian Ocean)
Can you drink seawater?
No—not as a source of drinking water.
You can physically swallow seawater, of course, but you cannot safely use it to satisfy your thirst.
In fact, drinking enough seawater can kill you.
The human kidneys cannot produce urine that is as salty as seawater.
That means that when your body takes in a large amount of seawater, it has to use some of its own fresh water to get rid of the excess salt.
You may therefore lose more water through urination than you gained by drinking the seawater.
You become increasingly dehydrated while becoming increasingly thirsty.
Eventually, severe dehydration can become fatal. NOAA specifically warns that drinking seawater can be deadly. (National Ocean Service)
So if you were stranded at sea with nothing to drink:
Do not drink the seawater.
Why can ocean animals drink it?
Because they aren't human beings.
Marine animals have evolved specialized systems for dealing with salt.
Some fish excrete excess salt through their gills.
Marine reptiles such as sea turtles have salt glands.
Marine mammals such as whales have different physiological adaptations that allow them to maintain their internal salt and water balance.
Their bodies are designed for the environment in which they live.
That doesn't mean seawater is harmless to them. It means they have evolved mechanisms that allow them to cope with it.
What else is salt used for?
Salt has an astonishing number of uses.
Food preservation
Before refrigeration, salt was one of humanity's most important preservation tools.
It has been used for:
meat
fish
vegetables
cheeses
pickles
Salt helps preserve food by making the environment less favorable to many microorganisms.
Cooking
Salt doesn't merely make food taste salty.
It can enhance and balance flavors.
A tiny amount can make sweetness taste sweeter and bring out flavors that otherwise seem muted.
Pickling
Salt is important in many traditional pickling and fermentation processes.
Deicing roads
Rock salt is spread on roads during winter because dissolved salt lowers the freezing point of water.
That helps melt ice under appropriate conditions.
Water softening
Salt is used in many water-softening systems.
Chemical manufacturing
Salt is an important raw material for producing numerous industrial chemicals, including chlorine and sodium hydroxide.
Medicine
Salt solutions are used in medical settings, including various forms of saline solution.
Animal nutrition
Sodium and chloride are essential nutrients for many animals.
Salt blocks are sometimes provided for livestock and other animals.
Leather processing
Salt has historically been used in preparing and preserving animal hides.
Cleaning
Salt can be used as a mild abrasive and is included in some traditional cleaning methods.
Ice cream making
Here's a fun one.
Salt mixed with ice can produce a colder ice-salt mixture than ordinary melting ice.
This is why salt has traditionally been used around the outside of an ice-cream maker.
The salt isn't added to the ice cream.
It helps create the cold environment that freezes the mixture inside the container.
Salt can even preserve history
Salt has played a remarkable role in archaeology.
In exceptionally dry or salty environments, objects and even organic materials can sometimes survive that would normally decay.
Ancient salt mines have preserved evidence of human activity for thousands of years.
One of the most famous examples is the discovery of remarkably preserved bodies associated with ancient salt mining, sometimes called salt mummies.
Salt can be both a destroyer and a preserver depending on the circumstances.
Why does salt taste so good?
There is a biological reason.
Our bodies require sodium, so humans evolved mechanisms that detect salt.
Our taste system is particularly sensitive to salty substances.
A small amount of salt can make food taste much better.
But there is an interesting twist.
The same substance that makes a bowl of soup delicious can become unpleasant when there is too much.
Take a sip of seawater and your tongue immediately knows:
This is not soup.
Is salt really a mineral?
Yes.
Naturally occurring sodium chloride is the mineral halite.
Halite forms crystals, often cubic ones.
If you have ever looked closely at coarse salt, you may notice that the crystals have remarkably straight edges and corners.
That isn't accidental.
It reflects the arrangement of sodium and chloride ions in the crystal lattice.
At the microscopic level, ordinary salt is an enormous three-dimensional structure in which positively charged sodium ions and negatively charged chloride ions are arranged in an orderly repeating pattern.
Why does salt melt ice?
This is another delightful bit of chemistry.
Pure water freezes at about 32°F (0°C).
When salt dissolves in water, it interferes with the formation of the orderly ice crystal structure.
As a result, the freezing point is lowered.
That's why salt can help melt ice on roads and sidewalks when temperatures aren't too low.
There is a limit, however. Salt doesn't magically melt ice at any temperature. As temperatures become extremely low, ordinary road salt becomes much less effective.
Salt is both ordinary and extraordinary
A handful of salt doesn't look particularly impressive.
It is just a few white crystals.
But consider what those crystals represent.
Salt helped preserve food before refrigerators existed.
It helped ancient peoples survive.
It became an important commodity traded across continents.
It is buried beneath our feet in deposits created by vanished seas.
It fills the oceans.
It is inside every human body.
It allows nerves to transmit signals and muscles to contract.
It determines whether a fish can survive in a particular body of water.
It helps a sea turtle remove excess salt from its body.
It can melt ice.
It can preserve food.
It can manufacture chemicals.
And yet, if you drink too much of the water in which salt is dissolved, that same substance can contribute to your death from dehydration. (National Ocean Service)
Perhaps the most remarkable thing about salt is that life depends upon getting the balance right.
The ocean has its salt.
A freshwater lake has very little.
A fish has its own carefully regulated internal chemistry.
A human body has its own.
And all of them must maintain the right balance between water and dissolved minerals.
Salt may be one of the simplest substances in your kitchen, but its story reaches from ancient oceans and underground mountains of rock salt all the way into the microscopic workings of your own nerves and muscles.
That is quite a lot of history and science for something that fits inside a salt shaker.
Salt is both ordinary and extraordinary.
ReplyDeleteA nonsensical story is both ordinary and extraordinary.
The key lies in the balance of more and less.