What makes a chocolate-covered pretzel such an insanely tasty concoction? The English language is curiously lacking in a word for something that's both sugary and salty, but fortunately science has some answers. Image: Michael Dimmuno / Shutterstock
There are five basic tastes that a person can pick up on: sweet, salty, bitter, sour and savoury / umami. For a while, people thought that the tongue was divided up into little subdivisions, that only sensed one individual flavour. But, it turns that the whole tongue can taste all five flavours. Some of those flavours (like sugar or salt) might signal a food that is either kilojoule or nutrient dense, while other flavours (an excess of bitterness or sourness) might signal a food that might make you sick.
Image from Mushitza
The Flavour Layer Effect
The deliciousness of sugar and salt in combination might merely be down to a layering effect: the combination of the delight of one delicious flavour (salt!) with another delicious flavour (sugar!), yielding a delight two times greater than either one alone. Barb Stuckey, a professional food developer and the author of TASTE: Surprising Stories and Science About Why Food Tastes Good, explained it to us like this:
We like sweet because it signals calories, or energy, to us. And we like salt because we need it for normal bodily function. We have no sodium storage system, as we do with other minerals (i.e. we store calcium in our bones), so Mother Nature's solution is a built-in craving for it. The combination of these two positive biological responses is VERY pleasurable. To use an analogy, it's akin to hearing beautiful music while sniffing rose petals: two positive sensory stimuli.
Image from America's Test Kitchen
Taste Receptor Activation
Of course, salt is not just a taste, it's also a taste enhancer. And, while taking a bit of salt with a sweet flavour can make the sweetness all the more intense, too much salt combined with sweetness can be truly terrible. The explanation for this may lie in how salt interacts with the tongue's other taste receptors. A study in Nature found that high-salt levels activate not only salt taste receptors, but also both bitter and sour taste receptors. So that "yuck" reaction to a biscuit that's too salty may be a reaction to the sudden sense of bitterness and sour in your mouth, too.
Image from Karen in the Kitchen
The way we taste and how we interpret it isn't all down to physiology. Cognitive processes also have a hand in it. In his article "Why You Like What You Like" for Smithsonian magazine, Tom Vanderbilt identifies the "mere exposure effect", the cognitive reaction that makes us appreciate things more the more we experience them. In other words, we like what we like -- after encountering it enough times.
But, it turns out that the mere exposure effect is not an equal opportunity actor. While single-note flavours (for instance, just sweet or just salty) bore us after repeated tastings, Vanderbilt says that more complicated, blended flavours entice us more and more each time we try them.