Science of Salt

We have become a salt-obsessed society, but maybe we can blame our ancestors for that?

I cannot count how many times I thought a meal was just meh, but with a pinch of salt it magically turned into a dish full of deep and vibrant flavours. This is a great trick for anyone who, like me, isn’t an especially talented cook.

“Salt is so common, so easy to obtain, and so inexpensive that we have forgotten that from the beginning of civilization until about 100 years ago, salt was one of the most sought-after commodities in human history.”
—Mark Kurlanksy in A World History of Salt

It’s thought that humans began adding salt to their foods between 5,000–10,000 years ago, mainly to help preserve the food. An unforeseen consequence was that it also led to a worldwide acceptance and expectation of salty tasting food.

But there’s something special about salt. It doesn’t just make food salty. It’s more of a flavour enhancer, and is added to sweet as well as savoury foods. Salt pairs with nearly everything in our diet.

And it isn’t just humans who are salt-obsessed: Japanese macaques, a small primate species, have learned to dip potatoes in saltwater instead of freshwater. Apparently, the monkeys also enjoy how salt improves food.

It’s ubiquitous. Across cultures and across time.

To a scientist, a salt is the combination of a positive ion like sodium (Na+) and negative ion like chloride (Cl-). It’s a general term for an entire group of compounds that includes calcium chloride, magnesium chloride, and potassium chloride.

To the rest of us, “salt” is the salt chemically known as sodium chloride (NaCl) — the white crystals in your salt shaker or kitchen. Sodium chloride just happens to be the most popular salt in our diet, so we’ve commonly come to refer to it simply as salt, as will I for the rest of this article.

Any salt compound can trigger our salt perceiving taste buds, but sodium chloride gives us the flavor we crave the most. It’s so much more versatile than just a provider of salty taste: it enhances virtually everything.

You probably recognise from your own experience what a difference salt makes. Imagine any dish without salt — even your most favourite — and it would seem lacklustre. Bread, soup, tacos, pad thai, pizzas, and even croissants all rely on that little sprinkling of salt to be able to work their magic.

Study after study has shown that salt enhances the overall palatability of food. When salt is added to soup, it’s perceived as thicker, fuller, and better balanced. It masks bitter and metallic off-flavors while accentuating sweetness. It has been shown to influence the aroma or odour of the food. It interacts with our saliva and alters the mouthfeel of what we’re eating.

How a simple molecule like salt could influence such varied aspects of our culinary experience is still a mystery, but one thing is fairly obvious: salt imparts so much more than saltiness to food.

About 5,000 years ago, the Chinese realized that salt could be used to preserve food. This was a huge breakthrough, because it meant that food could be stored all winter without spoiling. Humans no longer had to follow packs of animals during the winter months and small settlements could lay down permanent roots in certain areas.

Salt was the key that opened the door to settled civilization, making salt a precious and sought-after commodity. The first villages began near salt sources, and it was valued akin to money in these early societies. In fact, in ancient Rome, government officials and soldiers were paid with “salarium” or salt money.

Huge efforts were exerted to obtain it: mules would drag it across continents, the Elbe-Trave canal, which required 17 locks, was built in Germany in 1278 to accelerate its trade, and the first tunnel built through the Alps in 1480 was used to transport it.

The ancient Romans considered salt to be sacred, placing it on the table before any other food. At a traditional English dinner, guests of higher rank would be seated closer to the salt shaker. And perhaps most notably, Christ referred to his followers as the most respected and noble people by saying:

“Ye are the salt of the earth.”

Omnivores can eat anything. From leaves and plants to meat and fish, there are plenty of food choices open to them — and us. But taste is thought to have played an especially important role in keeping us alive, acting as a way for our hunting and gathering ancestors to identify safe and nutritious foods.

Human babies are born with a natural desire for sweet tasting foods. Historically, sweet foods like fruit would have been high in sugar, nutrients, and energy, so this was an excellent instinct.

On the other hand, a preference for bitter foods like coffee or beer is developed with age. Most young children have an aversion to even slightly bitter foods. This is likely the remnants of a defense mechanism against many toxic and poisonous plants — which also have a bitter taste. In this case, a repulsion to bitter foods might have been the difference between life and death.

Our taste buds have the capability to distinguish between sweet, salty, bitter, sour, and umami, but evolution has taken other species on very different paths.

Animals that have a very specialized diet, like koalas, who only eat eucalyptus, or pandas, who only consume bamboo, have lost the diversity in their taste buds. If all they ever eat is one thing, they’re unlikely to ever be tripped up by eating toxic or poisonous food.

Evidence also lies within the genes of big cats, where entire species have lost their sweet-perceiving taste buds. Since these animals are carnivores, the sweet receptors likely lost any advantage or function to these animals: it was no longer necessary for survival. Some carnivorous aquatic creatures have actually lost nearly all their taste receptors — sea lions swallow their prey whole without any tasting, no longer relying on taste buds to help them identify nutrients. It’s more likely that visual cues like animal movement and swimming help guide sea lions to nutritious food sources.

It seems our ability to identify different tastes like saltiness must’ve been preserved for a reason.

Today, salt is considered a killer. It leads to heart disease, kidney failure, high blood pressure and a whole host of other diseases that could be prevented just by cutting down on salt.

This is entirely true.

But here’s another: if we stopped eating salt tomorrow, our body would shut down. It isn’t just some sort of storybook demon; we also need it to live.

Each day our body requires anywhere from 180–230 mg of sodium. The sodium ions, Na+, act as a regulator in our body, balancing the pressure within and outside cells. Without this, every single cell in our body would get off-kilter. As you might expect, this has widespread effects including changes in muscle and nerve activity, kidney function, and cardiac efficiency.

Your body would quickly respond by signalling the kidneys and sweat glands to conserve any water within the body, because water is the reservoir that holds sodium. A pinch of salt is all that’s needed to keep us healthy, and our bodies have become very efficient at making sure we have it.

The problem is that our bodies are not nearly so diligent when it comes to removing excess salt.

To get salt out of our body, the kidneys, which filter unwanted material out of our blood, will try to flush salt out of the system. This is done by producing larger amounts of salty urine. If so much salt is consumed that the kidneys can’t remove it, the sodium in our blood stream must be diluted with water. The additional water added to blood means the heart now has a larger volume of blood to circulate. This makes the heart work harder to pump the increased amount of blood throughout our body.

This mechanism is exactly why excess salt leads to health problems. It puts more stress on our body because the heart and kidneys need to work harder, and your arteries thicken their walls to deal with the extra blood pressure.

With all the unpleasant images this little medical detour has conjured up, you might be scouring your diet for where excess salt is sneaking in.

The answer, or about 80% of the answer, is this: processed foods.

Why can’t we just replace NaCl in foods?

Well, we could substitute other mineral salts like potassium chloride (KCl), calcium chloride (CaCl), or Magnesium (MgCl) into our food, but none of these replacements measure up to our expectations of salt. Instead of sodium chloride’s clean taste, you’d have added bitter, metallic and chemical tastes.

Yuck.

This means we can only partially replace NaCl in foods or these repulsive off-flavors become noticeable.

Another problem is these salt substitutes don’t function as well as sodium chloride. For example, potassium chloride doesn’t cover up bitter tastes quite like sodium chloride does. So, even though it does trigger our salt receptors, just like NaCl, it doesn’t mask the off-flavors like good ole’ NaCl does.

Since there seems to be no direct substitute for salt, food scientists are getting incredibly creative when it comes to reformulating products to be low sodium.

Apparently, coarser grained NaCl will intensify the saltiness perception and impact compared to smaller grained salt. Adding this coarser salt later in the manufacturing process has been correlated to enhanced saltiness delivery to the mouth.

Another idea has been to alter the food itself, rather than the salt. This could work since food is really a matrix used to hold the salt, and if food released the salt to our taste buds more easily, perhaps taste perception could be increased? Interesting patterns have been found by researchers: for example, spreading salt out unevenly through sandwiches and snack mixes made them seem significantly saltier, even though the same salt content was used.

When it comes to processing food, there’s no easy answer to replacing salt. At least not yet. So, in the meantime, curbing the amount of processed food in your diet seems like the best way to stop wreaking havoc on your heart and kidney.

Adding salt to foods seems to be the one aspect of cuisine that spans all cultures and continents, and this makes sense considering that salting food and the salt trade laid the foundation for civilized society. And although our salt-perceiving salt buds may have historically helped our ancestors survive, there’s no doubt salt seems to be contributing to the demise of our health in the present day.

But this is nothing new: salt has always led some societies to reign and others to their ruin.

Perhaps some things never change?