Spicy isn’t a taste. It’s pain.
Chilli “heat” triggers the same receptor that detects a burn. Birds can’t feel it, and that seems to be the point.
Taste buds detect sweet, sour, salty, bitter and umami. Chilli heat isn’t on the list. Capsaicin binds to TRPV1, a receptor on pain-sensing nerves whose usual job is to warn you about dangerous heat above about 43 °C.
So when you eat a hot pepper, your nerves report, quite accurately as far as they can tell, that your mouth is on fire. That’s why water doesn’t help much (capsaicin is oily) while milk and yoghurt do: the fat and the protein casein help wash it away.
The same family of receptors explains mint: menthol triggers TRPM8, the cold sensor, which is why mint feels cool.
Why chillies are hot at all
Mammals tend to chew seeds and destroy them. Birds swallow them whole and drop them far away. Bird TRPV1 receptors don’t respond to capsaicin, so birds eat the hottest peppers happily. One leading hypothesis is that capsaicin deters the wrong seed dispersers and leaves the right ones alone.
Humans broke the arrangement. We learned to enjoy the burn, possibly because of the endorphin response, the thrill of a safe danger, or plain cultural habit, and we carried chillies around the world within a century of 1492.
A Nobel Prize
David Julius used capsaicin to find the TRPV1 receptor. It earned him a share of the 2021 Nobel Prize in Physiology or Medicine.
Bring it up
“Chillies evolved to burn mammals but not birds. Birds are better at spreading their seeds.”
Follow the thread
- RelatedCarrots used to be purple Both show how the plants on our plate were shaped by evolution and by human selection.
- RelatedThe croissant is Austrian (sort of) Another familiar food with a surprising backstory.
- RelatedBefore 1492, Italy had no tomatoes and Thailand had no chillies Why chillies are hot, and why people around the world learned to love them.
- RelatedOctopuses have three hearts and blue blood Another case where a chemical detail (copper blood, pain receptors) explains a creature’s behaviour.
- In contrastSichuan pepper makes your lips buzz at 50 Hz Chilli triggers heat-pain receptors; Sichuan pepper triggers touch receptors. Málà combines both.
- RelatedUmami: the taste discovered in a bowl of soup Two cases where a chemical in food was traced to a specific receptor on the tongue.
