Some Like It Hot! How to Measure a Chilli’s Heat

Anyone who has ever enjoyed spicy food can attest to the fact that not all chillies are created equal. They can range from a comfortable hint of warmth and flavour, all the way through to the rather extreme sensation of mouth-burning and throat-clutching agony.

Many restaurants and supermarkets provide a handy little chart to indicate the heat level of a chilli or a meal containing this fiery ingredient. But how is the heat of chilli measured?

It actually requires some rather serious science. Two tests are used to quantify the heat level of chilli - the Scoville Organoleptic Test and High Performance Liquid Chromatography (HPLC).

These two analyses both seek to measure the amounts of a particular group of chemicals that give chillies their heat. These chemicals are called capsaicinoids and they are found in different quantities in every type of chilli pepper. Capsaicinoids are unique because they irritate tissue by producing a burning sensation. Have you ever noticed your fingertips stinging after touching a Scotch Bonnet chilli pepper? That sensation is caused by the presence of capsaicinoids.

Scoville vs. HPLC

The Scoville Test is essentially an advanced taste test. In order to determine the heat, a mixture of ground chilli and sugar is dissolved in water. It is then tasted at intervals as it becomes more and more dilute. The more dilutions required to lose the heat, the hotter the chilli.  

Unfortunately, this is a rather subjective test. Some people can stomach the hardiest of chillies without so much as a wince while for others the merest whiff can get eyes watering. It does however provide a rough estimate.

This is where the HPLC method is helpful, as it provides an alternative and possibly more accurate reading of capsaicinoids levels. HPLC is a form of chromatography - a process used to divide a substance into its separate parts. Chromatography is used to investigate food for many different reasons, such as analysing for Artificial Colorants and Nitrosamines.

In this HPLC method, a chilli is first dried and ground. A sample of it is then combined with a solvent, which is passed through a steel column before reaching a detector. The detector identifies which compounds are present, and how much there is of each before putting the results in a graph called a chromatogram.

To measure the heat of a chilli, it is necessary to determine which capsaicinoids are present and how much there is of each. Generally, the greater the amounts of any capsaicinoids, the hotter the chilli will be, although some capsaicinoids are hotter than others. The result is measured in Scoville units, in honour of Professor Wilbur Scoville, who developed the dilution test.

So which chillies are the hottest? Sweet bell peppers are, unsurprisingly, very mild, racking up zero Scoville units. On the other end of the scale is the Ghost Pepper, weighing in at over a million Scoville units - not one for the faint hearted!

Image Source: Chilli Peppers