Why does mint make your mouth feel cold, and why do chillies taste hot?

It’s a favourite ice cream flavour and garnish of cold drinks, but does mint really taste ‘cool’? And what about chillies – how similar is that ‘heat’ to physical heat?

In fact, there’s a scientific reason people describe mint as ‘cool’ and chillies as ‘hot’: it’s all to do with the receptors in the mouth.

Why does mint taste cold and chillies taste hot?

“There are two main taste nerves that innervate the tongue and the palate and some of the throat,” explains Dr John Prescott, a conjoint professor at the University of Newcastle and director of research and consultancy company TasteMatters.

“But there are also nerves that belong to what is called the somatosensory system, which is the touch system – the same system that receives information about touch anywhere on the body has nerves present in the mouth.”

Most of these sensors come from the trigeminal nerve, which provides sensation to the face – especially the mouth, nose and eyes. It provides receptors to the mouth that are sensitive to pain, pressure, and hot and cold temperatures.

“In the case of the cold receptors, there are specific receptors, called TRPM8 receptors, that respond to compounds like menthol, which is found in mint,” explains Prescott.

“These cold receptors get activated by the chemical structure of menthol, and it’s perceived in exactly the same way that a glass of cold water would be perceived.”

So mint sends the same signal to your brain that an ice cube would: cold.

This is also true of chillies and heat: that spiciness is the capsacin in chillies activating your heat and pain receptors.

There are compounds in mustard, garlic and onions that also activate these heat and pain receptors. And there are plenty of foods that activate other somatosensory reactions too.

What other foods trigger tactile feelings?

“If you go to your kitchen cupboard and your fridge, if it’s reasonably well stocked, you could probably pull out a dozen or 20 different foods that contain compounds that activate the tactile sensors in the mouth, or nose,” says Prescott.

The most likely candidate in your pantry is table salt, which has an irritating effect – but there are plenty of other flavours that induce weirder reactions.

Sichuan peppercorns are one: they activate the tactile sensors in the mouth, which produce a buzzing feeling – “sort of like putting a battery on your tongue a little,” says Prescott.

Carbonated beverages do a similar thing.

“That’s got nothing to do with the bubbles, by the way,” says Prescott.

“It’s to do with the fact that the carbon dioxide gets converted to carbonic acid, and it’s the acid which produces that that sensation on the tongue when we drink.”

So, it’s possible to get the bubbly taste of a fizzy drink without bubbles – indeed, a 2013 study found that people thought bubble-free drinks with added carbonic acid tasted the same as bubbly drinks.

Ethanol molecules, or alcohol, also activate the somatosensory system.

“One of the reasons why low alcohol or no alcohol beer or wine is not well accepted is because it doesn’t have the bite that produced by alcohol,” says Prescott.

Because the trigeminal nerve innervates the nose and eyes as well as the mouth, many of these foods can affect other parts of your face. This, says Prescott, causes wasabi’s pungency in the nose – and also explains why rubbing your eyes after handling chillies is such a painful experience.

So why do we eat this stuff?

If all of these foods cause pain and pungency, why are they so popular? It’s hard to imagine Indian or Chinese cuisine without chilli, but up until a few centuries ago, the plant was exclusive to South America.

“Chilli was exported from Europe to India and Southeast Asia, for example, where it absolutely took off,” says Prescott.

“One of the questions that I’ve always found interesting is: why did it take off so much? People have all sorts of sort of hypotheses about that.

“They say it’s popular in tropical climate because it makes you sweat and cools you off. Or it may be a good source of vitamin C. Or it may be that if you eat a staple food, like corn, or rice, and so on, it adds a bit of interest to those products. It’s hard to know which of any of those is true. But maybe it’s a combination.”

Whatever the reason, it’s certainly the case that all of these sensations are a critical part of food’s taste.

“If we if we took away those sensations, a lot of our food and our drinks would be pretty flat tasting,” says Prescott.

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