If you’ve ever tasted a really hot chilli you’ll know just how potent the effects can be. The burning heat sensation on the lips, on the tongue – and if you are not careful, on other more sensitive areas, such as the eyes – can be severe and last for a painfully long time.
The chemical that causes this effect is capsaicin, one of a host of very similar compounds, collectively known as capsaicinoids, all of which contribute to the taste and effects. Chilli fruits vary enormously in their pungency – in other words, how much capsaicinoid is present – and it is useful to have a reliable guide to what you’re putting in your mouth.
The first person to try to assess this scientifically was an American pharmacist working at the start of the 20th century, Wilbur Scoville. If the name rings a bell, it is because chillies are now commonly rated on the “Scoville” scale.
In 1912, Scoville didn’t have access to modern analytical equipment, so he did the next best thing – he used the human taste bud. His method was, in essence, very simple. He dried the chillies, ground them to a powder and macerated a grain of the powder overnight in alcohol. The resulting alcoholic solution was then diluted sequentially with sugared water: 1ml of solution diluted in 100 ml of water, then 2ml in 100ml, and so on. Starting with the most dilute, the solutions were then tasted, until “a distinct but weak pungency is perceptible on the tongue”.
This level of dilution would become the Scoville rating for that chilli. The higher the level of capsaicinoids present in the chilli, the more the alcohol solution would need to be diluted, and thus the higher the Scoville rating.
There are obvious limitations to this method, not least that everyone’s taste buds are different, and any two people tasting the same solution may perceive them very differently. To some extent this can be overcome by using a panel of testers, and take the point at which the majority agree that a solution has detectable pungency.