The Scoville scale is a measure of the hotness of a chilli pepper. These fruits of the Capsicum genus contain capsaicin, a chemical compound which stimulates thermoreceptor nerve endings in the tongue, and the number of Scoville heat units (SHU) indicates the amount of capsaicin present. Many hot sauces use their Scoville rating in advertising as a selling point.

It is named after Wilbur Scoville, who developed the Scoville Organoleptic Test in 19121. As originally devised, a solution of the pepper extract is diluted in sugar water until the 'heat' is no longer detectable to a panel of (usually five) tasters; the degree of dilution gives its measure on the Scoville scale. Thus a sweet pepper, containing no capsaicin at all, has a Scoville rating of zero, meaning no heat detectable even undiluted. Conversely, the hottest chiles, such as habaneros, have a rating of 300,000 or more, indicating that their extract has to be diluted 300,000-fold before the capsaicin present is undetectable. 15 Scoville units is equivalent to one part capsaicin per million. Thus the highest concentration of pure 100% capsaicin corresponds to 15,000,000 Scoville units. The greatest weakness of the Scoville Organoleptic Test is its imprecision, because it relies on human subjectivity.

Later analytical developments such as high performance liquid chromatography (HPLC) (also known as the "Gillett Method") have now enabled the Scoville rating to be dete...