This is the first in the new ‘Kitchen Science’ series, providing the answers to everyday questions that might occur to you while you’re dancing around the kitchen, stirring sauces, kneading doughs, beating eggs and singing loudly.
So, our first ever Kitchen Science contains the answer to the burning (see what I did there? Yes.) question, why are chillies hot? Some people love it, some people hate it, but everyone has felt that eye-watering, mouth-burning chilli sensation. So what causes it? Why do chillies set us on fire? Why do people love the sensation? And, for those who don’t love it, how can you please make it stop?
The burn in chilli is caused by a chemical called capsaicin. It’s a fairly simple wee thing, doesn’t look like much on paper, but when it comes into contact with certain receptors, you know about it. Humans (and other mammals) have a group of receptors known as the vanilloid receptors. Capsaicin binds to vanilloid receptor subtype 1 (VR1, also known, confusingly, as TRP1).
TRP1 is what is known as an ion channel, this means that when it exists in two states, open and closed. TRP1 is closed in its resting state, just sitting around, binding site open and willing to receive a friendly molecule for a little cuddle. If a capsaicin molecule happens along, and binds to TRP1 for a molecular hug, the channel opens, and ions are able to pass through. Ions are charged molecules, and they always want to spread their charged love, always moving from an area of positive charge, into an area of negative charge (or vice versa), whenever they can. This causes depolarisation, the change from a negative, polar environment to a neutral or slightly positive, and thus less polar, environment. This depolarisation of the nerve cell triggers a message to be sent to the brain. In this case, the message is “ouch, that’s really hot”.
TRP1 doesn’t exist simply so we can feel chilli heat. The channel also opens under other stimulation, for example high temperatures or severe physical abrasion. TRP1 receptors are responsible for the sensation of friction burn, and indeed actual heat burn. Their primary purpose is actually to protect the body from things that burn, so they are alert and ready to tell you to “get your hand away from that very hot thing, you daft person”. It seems to be merely coincidence that the capsaicin molecules produced by chilli peppers happen to bind to the receptor, thus causing a similar sensation of heat.
Or is it coincidence? Chillies produce capsaicin as a defence mechanism, to stop mammals from eating them. Chillies would prefer to be eaten by birds, because mammalian digestive systems destroy chilli seeds, whereas avian digestive systems tend to leave the seeds intact, so when they make it out the other end, they can grow again, in a new location. Chillies then, have evolved a mechanism to try and discourage mammals, with their over-enthusiastic digestive systems, from eating them. And that’s not the only reason chillies like to be hot, increased potency also helps to protect against a fungus that grows on chilli flesh; this may be even more of an evolutionary driver than the big hungry mammals.
While some people revel in the chilli burn, others (like me) just can’t stand the heat. Personally, a very hot chilli-related dish can result in me with my tongue under the cold tap, flapping like a demented chicken. And actually, this is fairly daft behaviour on my part, because water isn’t a brilliant way of stopping chilli burn. The issue is that your mouth isn’t actually hot, the capcaisin has just fooled it into thinking that it is. You don’t need to cool your mouth down, what you need is to get rid of the capsaicin. And capsaicin is hydrophobic, it doesn’t like water. This means that capsaicin won’t dissolve in water, what it needs is a fat-based liquid such as milk, cream or yoghurt. Capsaicin can dissolve in the fat-based liquid, and be washed away, leaving your mouth feeling cooler. Next time I accidentally eat something far too hot for me (a regular occurrence because my husband has a mouth that I can only presume is coated in steel and likes chilli in EVERYTHING), I’m going to bypass the cold tap and just go at a tub of ice-cream. Because science says that I should, and I love science best of all when it says I should eat ice-cream.