The Scoville scale is a measure of the hotness or piquancy of a chili pepper. These fruits of the Capsicum genus contain capsaicin, a chemical compound which stimulates chemoreceptor nerve endings in the skin, especially the mucous membranes. The number of Scoville heat units (SHU) indicates the amount of capsaicin present. Some hot sauces use their Scoville rating in advertising as a selling point.
The scale is named after its creator, American chemist Wilbur Scoville, who developed a test for rating the pungency of chili peppers. His method, which he devised in 1912, is known as the Scoville Organoleptic Test. An alternative method of quantitative analysis, known as high-performance liquid chromatography, directly measures capsaicinoids and attempts to relate the measured concentration in ppm to the Scoville scale using a mathematical conversion factor of 15, 20 or 30 depending on the capsaicinoid.
Spice heat is now usually measured by a method using high performance liquid chromatography (HPLC). This identifies and measures the heat-producing chemicals. They are then used in a mathematical formula in which they are weighted according to their relative capacity to produce a sensation of heat. This method yields results, not in Scoville units, but in ASTA pungency units. A measurement of one part capsaicin per million corresponds to about 15 Scoville units, and the published method says that ASTA pungency units can be multiplied by 15 and reported as Scoville units. This conversion is approximate, and spice experts Donna R. Tainter and Anthony T. Grenis say that there is consensus that it gives results about 20–40% lower than the actual Scoville method would have given.
Pungency values for any pepper, stated in Scoville units, are imprecise, due to expected variation within a species—easily by a factor of 10 or more—depending on seed lineage, climate (humidity is a big factor for the Naga as the Dorset Naga and the original Naga have quite different ratings), and even soil (this is especially true of habaneros). The inaccuracies described in the measurement methods above also contribute to the imprecision of these values. When interpreting Scoville ratings, this should be kept in mind.
|Scoville rating||Type of pepper|
|8,600,000-9,100,000||Various capsaicinoids (e.g. homocapsaicin, homodihydrocapsaicin, nordihydrocapsaicin)|
|2,000,000-5,300,000||Standard U.S. Grade pepper spray, FN 303 irritant ammunition|
|855,000-1,050,000||Naga Jolokia, Dorset Naga|
|350,000-580,000||Red Savina Habanero|
|100,000-350,000||Habanero chili, Scotch Bonnet Pepper, Datil pepper, Rocoto, Jamaican Hot Pepper , African Birdseye|
|50,000-100,000||Thai Pepper, Malagueta Pepper, Chiltepin Pepper, Pequin Pepper|
|30,000-50,000||Cayenne Pepper, Ají pepper , Tabasco pepper, some Chipotle peppers|
|10,000-23,000||Serrano Pepper, some Chipotle peppers|
|2,500-8,000||Jalapeño Pepper, Guajillo pepper, New Mexican varieties of Anaheim pepper, Paprika (hungarian wax pepper)|
|500-2,500||Anaheim pepper , Poblano Pepper, Rocotillo Pepper|
|0||No heat, Bell pepper|