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The Scoville scale is the measurement of the pungency (spicy heat) of chili peppers or other spicy foods reported in Scoville heat units (SHU), a function of capsaicin concentration. The scale is named after its creator, American pharmacist Wilbur Scoville. His method, devised in 1912, is known as the Scoville Organoleptic Test.
The Scoville scale is an empirical measurement dependant on the capsaicin sensitivity of testers and so not a precise or accurate method to measure capsaicinoid concentration, however, capsaicin concentration can very roughly be estimated as ~18µM/SHU.
In Scoville's method, a measured amount of alcohol extract of the capsaicin oil of the dried pepper is produced, after which a solution of sugar and water is added incrementally until the "heat" is just barely detectable by a panel of (usually five) tasters; the degree of dilution gives its measure on the Scoville scale. Thus, a sweet pepper or a bell pepper, containing no capsaicin at all, has a Scoville rating of zero, meaning no heat detectable. The hottest chilis, such as habaneros and nagas, have a rating of 200,000 or more, indicating their extract must be diluted over 200,000 times before the capsaicin presence is undetectable. The greatest weakness of the Scoville Organoleptic Test is its imprecision, because it relies on human subjectivity. Tasters are given only one sample per session. Results vary widely, up to 50%, between laboratories.
Spice heat is usually measured by a method that uses high performance liquid chromatography (HPLC). This identifies and measures the concentration of heat-producing chemicals. The measurements are used in a mathematical formula that weighs them according to their relative capacity to produce a sensation of heat. This method yields results, not in Scoville units, but in American Spice Trade Association (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. Scoville units are a measure for capsaicin content per unit of dry mass. 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.
|Scoville heat units||Examples|
|Scoville heat units||Examples|
|1,500,000–2,000,000||Trinidad Moruga Scorpion Carolina Reaper|
|855,000–1,463,700||Naga Viper pepper, Infinity Chilli, Bhut Jolokia chili pepper, Trinidad Scorpion Butch T pepper, Bedfordshire Super Naga, 7-Pot Chili|
|350,000–580,000||Red Savina habanero|
|100,000–350,000||Habanero chili, Scotch bonnet pepper, Datil pepper, Rocoto, Piri Piri Ndungu, Madame Jeanette, Peruvian White Habanero, Jamaican hot pepper, Guyana Wiri Wiri, Fatalii |
|50,000–100,000||Byadgi chilli, Bird's eye chili (aka. Thai Chili Pepper), Malagueta pepper, Chiltepin pepper, Piri piri (African bird's eye), Pequin pepper, Siling Labuyo (native chili cultivar from the Philippines)|
|30,000–50,000||Guntur chilli, Cayenne pepper, Ají pepper, Tabasco pepper, Cumari pepper (Capsicum Chinese)|
|10,000–23,000||Serrano pepper, Peter pepper, Aleppo pepper|
|3,500–8,000||Espelette pepper, Jalapeño pepper, Chipotle, Guajillo pepper, New Mexican peppers, Hungarian wax pepper, Tabasco sauce|
|1,000–2,500||Anaheim pepper (cultivar of New Mexican peppers), Poblano pepper, Rocotillo pepper, Peppadew, Sriracha sauce, Gochujang|
|100–900||Pimento, Peperoncini, Banana pepper, Cubanelle|
|No significant heat||Bell pepper, Aji dulce|
Since Scoville ratings are defined per unit of dry mass, comparison of ratings of between products having different water content can be misleading. Typical fresh chili peppers have a water content around 90 percent, whereas, for example, Tabasco sauce has a water content of 95 percent. For law-enforcement-grade pepper spray, values from 500 thousand up to 5 million SHU have been mentioned, but the actual strength of the spray depends on the dilution, which could be a factor of 10.
The chilis with the highest rating on the Scoville scale exceed one million Scoville units, and include specimens of naga jolokia or bhut jolokia and its cultivars, the "Jalapenó" and the "Ghost chili", neither of which has official cultivar status.
Numerical results for any specimen vary depending on its cultivation conditions and the uncertainty of the laboratory methods used to assess the capsaicinoid content. Pungency values for any pepper are variable, owing 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 Bhut Jolokia; 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.