Visual Argument

Visual Argument #1: The Science of Chili Heat

When you eat hot chilies, it can feel like your tongue is on fire. But unlike with a normal fire, water may not be the best choice to put out this one out. The Visual Argument team shows you how different «chili extinguishers» work, and gives you the scientific explanation behind them.

«The Science of Chili Heat»

By Lalah Rukh – journalist for Argument

Bite into a chili and your eyes instantly start watering, your nose starts running and your tongue seems in urgent need of a fire brigade. Instinctively you reach for a glass of cold water and gulp it down in one go. To your utter dismay, the water does little to extinguish the fire. Perhaps if you’d opted for something richer in fat, like a glass of milk, you would have fared better.

To find out why milk is more helpful than water, we need to dig deeper into the chili’s chemistry; whilst most chefs would argue that cooking is an art, the fundamentals of taste rely mainly on science.

What makes chilies hot?

A chemical compound named capsaicin (pronounced cap-say-sin), which belongs to the family of capsaicinoids, is what gives chilies their heat.

Capsaicin is a hydrophobic (water ‘hating’) molecule because of a long chain of carbon and hydrogen atoms attached to one of its ends. This tail-like structure makes capsaicin structurally similar to fats and insoluble in water. As ‘like dissolves like’, capsaicin is more readily soluble in fats and oils.

What drove the evolution of chili heat?

The capsaicin in chilies serves as an evolutionary defense mechanism, with the heat used as a powerful weapon to keep predators at bay, particularly the deadly fungus, Fusarium. Chilies seem to have no effect on birds as they lack the receptors to which capsaicin binds. This makes birds ideal candidates for dispersing chili seeds as their digestive system leaves the seeds intact.

Contrary to common perception, the hottest part of the chili is not its seeds, but the white flesh from which the seeds hang, called the placenta. Not all chilies are equally hot and that’s because apart from fending off their enemies, chilies also need to make the most of their limited water resources. In drier areas, less pungent chilies are more common as it makes sense to invest energy in conserving water rather than developing fungal defenses. Research shows that less hot chilies use water more efficiently as they possess fewer pores in their leaves, minimizing water loss by evaporation.

Fake Pain

In reality, chili isn’t a taste or flavour; it is, in fact, a kind of pain. Apart from the five kinds of taste receptors that make up our taste palette (sweet, salty, bitter, sour and umami), our tongue is home to thousands of pain receptors, called VR1 receptors, which are capsaicin’s main target. Capsaicin molecules bind to these pain receptors, sending a signal to the brain that causes the burning sensation. The same process happens when you get your hand too close to a hot fire – it burns! The only difference is that, in the case of chilies, it’s a false alarm; the capsaicin does not cause any physical damage to our tongues.

Pain against pain

Interestingly, capsaicin is also used to relieve pain. When capsaicin is applied repeatedly to the same part of the body it depletes a messenger molecule (labelled ‘P’), which carries the pain signal to our brains. Studies show that with the reduced production of P, the level of pain also drops. This explains why habitual chili eaters gradually develop a greater tolerance towards chili.

Why milk works best

If you want to enjoy a spicy curry without going through the processing of building up a tolerance, milk is your best bet because it contains a lipophilic (fat ‘loving’) protein called casein. Casein proteins are able to surround the fat-like capsaicin molecules, stopping them from binding to the pain receptors on your tongue, thereby slowly reducing the burning sensation in your mouth. The next time that tasty curry you’re enjoying starts making your eyes water, reach for a glass of milk and let the chemistry work its magic!