Spices have been part of human diets for thousands of years, and chilli peppers are now staple ingredients in many parts of the world. Chilli peppers are fruits and are part of the nightshade family, which contains members such as tomatoes, avocados and potatoes. Within this family lies the genus Capsicum that hosts peppers, a group of related species that are carefully cultivated to produce fruits with a spectrum of flavour and heat. From the mild bell pepper and the lively jalapeño to the unrelenting brutality of the Trinidad Moruga scorpion and Carolina reaper, peppers come in all ranges of spiciness. The heat, or pungency, of a chilli pepper is a product of its DNA, the environment it’s grown in and its ripeness. DNA can be changed by cross-breeding two species, followed by selective breeding of the offspring where the progeny with the desired traits are bred further. The stress imposed on the pepper, such as the temperature it’s grown in and the amount of water available to it, can likewise affect its pungency.Peppers also become spicier as they ripen from green to red.
While humans have learnt to manipulate and enrich pepper qualities, their spicy trait first evolved naturally as a defence mechanism. Rodents and mammals are equipped with receptors in their mouths that recognise the compound capsaicin – and other compounds collectively known as capsaicinoids – produced within chilli peppers. Capsaicin surrounds the seeds, which are needed for the plant to germinate its progeny, and the compound triggers the sensation of burning when consumed. This helps dissuade rodents and mammals from eating too much, with the latter being particularly threatening to the plant as they can grind and destroy the seeds as they eat the fruit. But birds, which do not grind the seeds and instead are useful helpers in dispersing them, are not sensitive to capsaicin and so are not discouraged from feeding. Capsaicin also wards off microorganisms from invading and decomposing the plant matter from the inside.
If capsaicin production and its spicy heat have evolved to deter hungry mammals from munching through peppers, then why do many humans ravenously ingest them? Spice serves a practical role in food by helping to prevent spoilage, but many of us who enjoy spice also like the challenging heat. While capsaicin triggers the sensation of burning and all its accompanying symptoms, such as sweating and mouth breathing, it can also trigger the release of endorphins that provide pleasure as a means to combat the pain.
However, the pleasure of eating spice is not there for all of us. The endorphin release does not happen for everyone equally, and for those who are sensitive to spice – or for spice lovers who overindulge – the pleasure can quickly recede while the pain intensifies. Unfortunately, the damage of too much spice doesn’t end in our mouths, as capsaicin can bind to receptors in our stomach and intestines. This can trigger diarrhoea as our body acts to protect itself by rapidly funnelling the irritant compound through the gut as quickly as possible. And in a case of true polar symmetry, the receptors that interpret capsaicin as heat at the beginning of our gastrointestinal tract are also there at the end, which is why we can also feel burning as we eliminate stool. Finally, as capsaicin is an irritant that also affects our outer organs, the abundant compounds in the spiciest peppers can elicit burning sensations when they come into contact with our skin and eyes. Chilli peppers can be as delicious as they can be harmful; the experience we have when eating them is determined by our tolerance – and the amount of capsaicin putting our receptors to the challenge.
In 1912, Wilbur Scoville created the Scoville Organoleptic Test as a means of measuring the amount of heat in a pepper. The method he developed was part quantitative and part subjective. Scoville gathered taste testers and asked them to taste a pepper’s capsaicin content – dissolved in an alcohol solution – mixed with sugar water. The capsaicin solution would be continually diluted with sugar water until heat could no longer be detected, which provided Scoville heat units (SHU). A pepper measuring 5,000 SHU would need to be diluted by 5,000 before no heat could be detected. Jalapeños measure between 3,000 and 10,000 SHU, whereas pure capsaicin measures 16,000,000.
The presence of capsaicin provokes a reaction from our brain as if we’ve come into contact with a high temperature food.
Capsaicin molecules released from the chilli pepper attach to specialist receptors on the tongue.
The bound receptors are connected to signaling cells known as neurons, which are triggered to send a signal to the brain.
The brain interprets the signals from the mouth as pain and heat from a high temperature.
To quell the pain, our brain stimulates the release of endorphins and dopamine that provide us with pleasure.
To combat the perceived scalding heat, we begin to sweat, open our mouths, and suck in cooling air.