Capsaicin: Why Chilies Burn and How to Cool Down
Capsaicin is the natural compound that makes chili peppers taste hot. It isn't a flavour or a true taste; it activates the same pain receptor in your mouth that responds to physical heat, so your brain reads it as burning.
How capsaicin "burns"
Your mouth, eyes and skin carry a receptor called TRPV1, whose normal job is to warn you of temperatures above roughly 43 °C / 109 °F. Capsaicin fits this receptor and switches it on without any real heat. Your body responds as if it's being burned: sweating, flushing, runny nose and a rush of endorphins, which is part of why spicy food can be addictive.
Because it's a pain sensation and not a taste, "spicy" isn't one of the five basic tastes.
Birds don't have a capsaicin-sensitive version of TRPV1, so they eat chilies freely and spread the seeds. Mammals, which would crush the seeds, get the burn.
Where the heat is
Capsaicin is produced in the white ribs (placenta) inside the pepper. Seeds pick some up by contact. Heat varies widely even within one variety, depending on growing conditions and ripeness.
Chili heat is measured on the Scoville scale:
| Chili | Approx. Scoville heat units |
|---|---|
| Bell pepper | 0 |
| Jalapeño | 2,500–8,000 |
| Cayenne | 30,000–50,000 |
| Habanero | 100,000–350,000 |
| Pure capsaicin | about 16,000,000 |
Cooking with capsaicin
- It's fat-soluble. Frying chilies in oil (chili oil, a tadka) carries the heat and flavour through a dish. Blooming chili flakes in fat gives a rounder, better-distributed heat.
- It's alcohol-soluble. Hot sauces and infusions with a little spirit extract it efficiently.
- It doesn't evaporate easily, but it does aerosolize. Searing chilies in a very hot pan can throw capsaicin into the air and make the kitchen cough. Turn on the fan.
Taming too much heat
To fix a dish that's too spicy, dilute it with more of the other ingredients, or add fat, dairy (yogurt, cream, coconut milk), sugar or acid. They don't destroy capsaicin; they compete with it and soften how you perceive it.
To cool your mouth, reach for milk, yogurt or something starchy like rice or bread. Cold water helps only for a moment.
Questions
Why does milk help with spicy food but water doesn't?
Capsaicin barely dissolves in water, so water just spreads it around. Milk contains fat that dissolves it and a protein called casein that helps pull it off your receptors.
Are the seeds the hottest part of a chili?
Not quite. Capsaicin is made in the pale ribs, called the placenta, that hold the seeds. Seeds taste hot because they're touching the placenta. Removing ribs and seeds both lowers the heat.
Does cooking make chilies less hot?
Capsaicin is quite heat-stable, so cooking doesn't destroy much. Long simmering spreads it through the whole dish, and added fat, sugar, acid and dairy make the heat feel milder.
How do I get chili burn off my hands?
Rub your hands with a little oil or dish soap, then wash with soap and warm water. Better still, wear gloves when cutting hot chilies, and don't touch your eyes.