The horsepower equivalent of measuring the strength of a chilli is the Scoville heat unit, or SHU. It is named after Wilbur L. Scoville, an American scientist who, in 1912, developed a test to measure levels of capsaicin, the chemical that creates the heat in chilli. Scoville diluted pepper extract in sugar water until the chilli's heat was no longer discernible. The resulting scale measures the degree of dilution – the greater the degree needed, the hotter the chilli.

Today's tests are more scientific, but Scoville's name lingers on. Pure capsaicin has a heat rating of 16 million SHU. Compare that with a standard Tabasco sauce, which registers 2,500 SHU, and which the inexperienced chilli eater might find unbearable. In 1994, Guinness World Records identified the Red Savina as the hottest chilli on earth. That was clearly throwing down the gauntlet – in 2007, the Red Savina's top heat rating was usurped by the Naga Jolokia. Meanwhile, Michael Michaud, a breeder from Dorset, developed a variety of his own. His Dorset Naga comes in at a palate-threatening 921,081 SHU.