Most people, if they're going to add anything to their coffee, choose the side of sweetness and cream. A touch of sugar or hazelnut syrup, perhaps a dash of cow's milk, all to help smooth out the rough, bitter edges of coffee.
But it might be worth your while to reach for something savory instead. A "hack" circulating on social media suggests adding a small pinch of salt, rather than a spoonful of sugar, to your morning (or afternoon or night, no judgment) cup of brew. This trick seems to remove some of the bitterness and brings out the other flavors that might otherwise be lost.
If the idea sounds odd to you, rest assured that it's not as strange as you might think. There is even a scientific basis for this quirk of coffee, well known for decades: Sodium chloride is extremely effective at suppressing bitterness in coffee and all kinds of food.
The ability of sodium chloride – ordinary table salt – to suppress bitterness has been attributed by scientists to salt's popularity as a cooking ingredient worldwide, throughout human history. By quashing the perception of bitterness, salt allows other flavors, such as sweetness or umami, to come to the fore and truly shine.
The tongue map theory of how humans taste was long ago debunked, but there are different receptors that are sensitive to specific types of flavors. The salt receptor is known as the epithelial sodium channel, or ENaC. Bitter taste receptors belong to a family known as TAS2Rs.
Research published in 1995 showed that salt is effective at masking bitterness. When the scientists mixed sweet and bitter compounds, adding salt made the mixture taste sweeter and less bitter. But the suppression didn't go both ways; the bitter compounds did not suppress the salt flavor.
It's still not entirely clear how the suppression works, but research on mice in 2013 found that, while ENaC tastes low levels of sodium chloride, at high concentrations, salt triggers the sour and bitter receptors, too. That's because this combination is thought to constitute an unpleasant taste, and consuming too much salt in one go is extremely dangerous.
But a little salt can go a long way. It used to be common, for example, to salt eggplants to reduce their overwhelming bitterness, a practice that's no longer necessary since we've bred out the bitterness. Salting is also a popular technique for reducing the bitterness of Brussels sprouts.
Coffee's bitterness emerges when it's roasted in preparation for brewing. This process forms compounds called chlorogenic acid lactones and, in darker roasts, phenylindanes, which result from the breakdown of chlorogenic acid.
Places around the world where salt is commonly added to coffee to enhance its flavor include Vietnam, where salty coffee is enhanced with condensed milk for a deliciously caramel-like brew. A Swedish Arctic coffee tradition is adding some salted meat or cheese.
Even members of the US Navy used to drink coffee with salt during and after World War II since their desalination equipment wasn't entirely effective, and they found that the salt helped with the bitterness.
So if you don't like your coffee sweet or milky, it could be worth experimenting with a pinch of salt, especially in situations where you end up with burnt coffee due to over-extraction. Since not everyone tastes things the same, you might need to experiment. Start with a small pinch, and adjust from there.
On the other hand, if you're trying to watch your sodium intake, you don't have to worry on that score, either. Sucrose (table sugar) and milk have also been found effective at suppressing bitter flavors.
Perhaps the Swedish were onto something with that cheese…