Analysis: how hot things get in your mouth depends on the capsaicin chemicals to be found in the chilli peppers in your food

This article is now available above as a Brainstorm podcast. You can subscribe to the Brainstorm podcast via Apple, Stitcher, Spotify or wherever you get your podcasts.

By Martin McHugh and Oisín Kavanagh, University of Limerick

Who would have thought that a YouTube channel where celebrities eat a series of increasingly spicy chicken wings would go viral?

Famously known as the "show with hot questions and even hotter wings," Hot Ones sounds like a ridiculous concept, but millions of subscribers tune in every week to see celebrities like Charlize Theron, Post Malone and Billie Eilish cough, cry, and even choke their way through a gauntlet of hot sauce-laden wings.

Connoisseurs of the show will already be familiar with the Scoville Scale. Utilised as a measure of pungency, some hot sauces featured on the show such as 'Da Bomb' and ‘Widow Maker’ have Scovile Heat Units of 135,600 and 682,000 respectively. For reference, jalapenos hit the scale anywhere between 2,500 to 8,000 units.

The Scoville Scale was originally devised by pharmacist Wilbur Scoville in 1912 and is a measure of Capsiacinoid concentration in chilli peppers. Capsaicin, a member of the Capsiacinoid chemical group, is the prominent active chemical compound found in peppers.

From an evolutionary perspective, these chemicals are designed to be a deterrent against ingestion by mammals. Any tissue that makes physical contact with capsaicin will feel a burning sensation.

The level or hotness of the burning is determined by the concentration of capsaicin present in the pepper. The fleshy tissue of the pepper contains the majority of capsaicin. This irritant is designed to protect the seeds, which are predominantly dispersed by birds.

Birds lack the mucous covered nerve endings that are impacted by the capsaicin and can consume chilli peppers without any problems. The chilli pepper seeds then pass through the bird's digestive track and are deposited in a new location.

From RTÉ Radio 1's Brendan O'Connor, spice expert, founder of Green Saffron and author of "Fresh Spice" Arun Kapil shares his easy tips for cooking with spices.

This is an example of a symbiotic relationship developed over time between birds and the peppers. Mammals, however, chew through the seeds and ruin any chances of germination. Therefore, natural selection may have enabled chillies with higher capsaicin concentrations to out survive other variants.

Although capsaicin causes a burning sensation in the mouth, it has also found a niche in dermal patches, creams and ointments as a pain reliever. It is often applied to the skin as a temporary relief for strains on muscles or joints and arthritis. In fact, while working for the Parke-Davis company, Wilbur Scoville devised the Scoville test when researching pain relieving creams.

In the original Scoville test, a weighed amount of dried pepper is submerged in an alcohol solution to extract the capsaicin. Once isolated, the chemical is then placed in increasingly diluted solutions of sugar water.

A range of dilutions are then given to a panel of five trained taste testers until a majority (three) find the dilution whereby they can no longer sense any spiciness. This subjective assessment is then used to determine the Scoville Heat Units present in the chilli.

Wilbur Scoville depicted as a Google doodle on January 22nd, 2016 on what would have been his 151st birthday. (Source: Google)

However, critics argue that Scoville units are too imprecise due to variations in taster's palettes and the numbers of heat receptors in the mouth. Another critique is that of sensory fatigue. Imagine attempting to distinguish between levels of spice when your mouth is already burning.

Nerves in the human body lose sensitivity after continued exposure to capsaicin and this is why some people are far more tolerant than others when it comes to spicy foods.

To combat this lack of accuracy, a new test was needed. This came about in the 1980s with the use of High-Performance Liquid Chromatography (HPLC). HPLC allows us to separate the variety complex molecules found in peppers and isolate the 'Hot one' (capsaicin).

Often it is attached to another analytical tool which allows us to then quantify this component within the mixture. HPLC is extremely accurate and can be used for all sorts of applications. Notably, HPLC can enable scientists to examine human hair and identify if an athlete has taken performance enhancing drugs.

This new analytical chemical test allowed scientists to derive a quantitative measure of Pungency Units. Pungency units can then be converted back to Scoville Heat Units. Approximately 1 part per million of capsaicin is 15 units on the Scoville scale (that's like finding a needle in a haystack).

We need your consent to load this rte-player contentWe use rte-player to manage extra content that can set cookies on your device and collect data about your activity. Please review their details and accept them to load the content.Manage Preferences

From RTÉ Radio 1's The Ray D'Arcy Show, ever heard of the Caroline Reaper chilli? it is the hottest chilli in the world clocking up a 2.2 million Scoville Heat Units. Ray along with 2Fm's Jenny Green and head chef at Aztec Cafe Hugh Camacho Romero all try it for the first time together.

With a more accurate assessment of pungency, chilli cultivators now compete to create the hottest variety of pepper in the world. The current Guinness World Record holder is the 'Carolina Reaper’. Approximately 200 times more powerful than Jalapenos, the Reaper hits the Scoville Scale at 2,200,000!

The internet is full of online challenges around the pepper including the ‘One Chip Challenge’. However, readers should be aware that the levels of capsaicin found in artificial peppers is far beyond what is found in nature and some participants have been hospitalised with headaches, stomach pain and vomiting. You’ve been warned!

In these online challenges a glass of milk is always nearby. That's because milk contains an enzyme casein that essentially chops up the capsaicin before it can get to the receptors on your tongue. On the other end of the scale alcoholic drinks can amplify the burning sensation.

So next time you load up an episode of ‘Hot Ones’ hopefully you will have a new, more scientifically informed viewing experience, rather than just watching red-faced celebrities struggling with ever increasing concentrations of capsaicin.

Dr Martin McHugh is an Education and Public Engagement Officer at the SSPC, the SFI Pharmaceutical Research Centre, at the Bernal Institute in the University of Limerick. Dr Oisín Kavanagh is a Pharmacist and Postdoctoral Researcher with the SSPC, at the Bernal Institute in the University of Limerick.


The views expressed here are those of the author and do not represent or reflect the views of RTÉ