Scoville scale

The Scoville scale is a measurement of the pungency (spiciness or "heat") of chili peppers, as recorded in Scoville Heat Units (SHU), based on the concentration of capsaicinoids, among which capsaicin is the predominant component.[3][4][5][6][7] The scale is named after its creator, American pharmacist Wilbur Scoville, whose 1912 method is known as the Scoville organoleptic test.[3][8] The Scoville organoleptic test is the most practical method for estimating SHU and is a subjective assessment derived from the capsaicinoid sensitivity by people experienced with eating hot chilis.[3][4]

"Scoville" redirects here. For other uses, see Scoville (disambiguation).
Pepper stand at Central Market in Houston, Texas, showings its peppers ranked on the Scoville scale
The Ghost pepper of Northeast India is considered to be a "very hot" pepper, at about 1 million SHU.[1]
The Naga Morich with around 1 million SHU[2] is primarily found in Bangladesh

An alternative method, using high-performance liquid chromatography (HPLC), can be used to analytically quantify the capsaicinoid content as an indicator of pungency.[3][5][7] As of 2011, the subjective organoleptic test has been largely superseded by analytical methods such as HPLC.[9]

Scoville organoleptic test

In the Scoville organoleptic test, an exact weight of dried pepper is dissolved in alcohol to extract the heat components (capsaicinoids), then diluted in a solution of sugar water.[3][10][11] Decreasing concentrations of the extracted capsaicinoids are given to a panel of five trained tasters, until a majority (at least three) can no longer detect the heat in a dilution.[1][3][10][11] The heat level is based on this dilution, rated in multiples of 100 SHU.[10]

Another source using subjective assessment stated: "Conventional methods used in determining the level of pungency or capsaicin concentration are using a panel of tasters (Scoville Organoleptic test method). ... Pepper pungency is measured in Scoville Heat Units (SHU) . This measurement is the highest dilution of a chili pepper extract at which heat can be detected by a taste panel."[4][12]

A weakness of the Scoville organoleptic test is its imprecision due to human subjectivity, depending on the taster's palate and number of mouth heat receptors, which vary widely among people.[1][4] Another weakness is sensory fatigue;[1] the palate is quickly desensitized to capsaicinoids after tasting a few samples within a short time period.[10] Results vary widely (up to ± 50%) between laboratories.[11]

Quantification by HPLC
The Red Savina pepper, a hot chili.[13]

Since the 1980s, spice heat has been assessed quantitatively by high-performance liquid chromatography (HPLC), which measures the concentration of heat-producing capsaicinoids, typically with capsaicin content as the main measure.[4][5] As stated in one review: "the most reliable, rapid, and efficient method to identify and quantify capsaicinoids is HPLC; the results of which can be converted to Scoville Heat Units by multiplying the parts-per-million by 16."[4][lower-alpha 1] HPLC results permit the measurement of a substance’s capsaicin capacity to produce perceived heat ("pungency").[5]

HPLC method gives results in American Spice Trade Association 1985 "pungency units", which are defined as one part capsaicin equivalent per million parts dried pepper mass. This "parts per million of heat" (ppmH) is found with the following calculation:[5]

Peak areas are calculated from HPLC traces of dry samples of the substance to be tested in 1 ml of acetonitrile. The standard used to calibrate the calculation is 1 gram of capsaicin. Scoville heat units are found by multiplying the ppmH value by a factor of 15.[5][lower-alpha 1] By this definition of ppmH, spicy compounds other than the two most important capsaicinoids are ignored, despite the ability of HPLC to measure these other compounds at the same time.[5]

An orally administered capsule of capsaicinoids claiming 100,000 Scoville units will correspond to around 6.6 mg of capsaicinoids per gram.[14]

Scoville ratings

Considerations

Since Scoville ratings are defined per unit of dry mass, comparison of ratings between products having different water content can be misleading. For example, typical fresh chili peppers have a water content around 90%, whereas Tabasco sauce has a water content of 95%.[15] For law-enforcement-grade pepper spray, values from 500,000 up to 5 million SHU have been reported,[1][16] but the actual strength of the spray depends on the dilution.[3] This problem can be overcome by stating the water content along with the Scoville value. One way to do so is the "D-value", defined as total mass divided by dry mass.[17]

Numerical results for any specimen vary depending on its cultivation conditions and the uncertainty of the laboratory methods used to assess the capsaicinoid content.[4] Pungency values for any pepper are variable, owing to expected variation within a species, possibly by a factor of 10 or more, depending on seed lineage, climate and humidity, and soil composition supplying nutrients. The inaccuracies described in the measurement methods also contribute to the imprecision of these values.[4][11]

Capsicum peppers

Capsicum chili peppers are commonly used to add pungency in cuisines worldwide.[3][4] The range of pepper heat reflected by a Scoville score is from 100 or less (sweet peppers) to over 3 million (Pepper X) (table below; Scoville scales for individual chili peppers are in the respective linked article).

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 "Dorset naga" and the "bhut jolokia", neither of which has official cultivar status.[18][19]

Scoville heat units Examples
1,500,000–3,000,000+Most law enforcement grade pepper spray,[20][21] Pepper X,[22] Carolina Reaper,[23] Dragon's breath[24]
750,000–1,500,000Trinidad moruga scorpion,[25] Naga Viper pepper,[26] Infinity chilli,[27] Ghost pepper[28]
350,000–750,000Red savina habanero[29]
100,000–350,000Habanero chili,[30] Scotch bonnet pepper,[30] Peruvian white habanero,[31] Guyana Wiri Wiri[32]
50,000–100,000Byadgi chilli, Bird's eye chili (a.k.a. Thai chili pepper),[33] Malagueta pepper[33]
25,000–50,000Guntur chilli, Cayenne pepper
10,000–25,000Serrano pepper, Aleppo pepper, Cheongyang chili pepper
2,500–10,000Espelette pepper, Jalapeño pepper, New Mexican varieties of Anaheim pepper[34]
1,000–2,500Anaheim pepper, Poblano pepper
100–1,000Banana pepper, Cubanelle
0–100Bell pepper, Pimento, Banana pepper

Capsaicinoids and TRPV1 agonists in general
The capsaicin "pharmacophore", the portion of the molecule that produces biological effects

The class of compounds causing pungency in plants such as chili peppers is called capsaicinoids, which display a linear correlation between concentration and Scoville scale, and may vary in content during ripening.[35] Capsaicin is the major capsaicinoid in chili peppers.[5]

The Scoville scale may be used to express the pungency of other, unrelated TRPV1 agonists, sometimes with extrapolation for much hotter compounds. One such substance is resiniferatoxin, an alkaloid present in the sap of some species of euphorbia plants (spurges). Since it is 1000 times as hot as capsaicin, it would have a Scoville scale rating of 16 billion.[36] In the table below, non-capsaicinoid compounds are italicized.

Scoville heat units Chemical Ref
16,000,000,000[lower-alpha 2] Resiniferatoxin [37]
5,300,000,000[lower-alpha 2] Tinyatoxin [38]
4,800,000,000[lower-alpha 2] Phenylacetylrinvanil
16,000,000 Capsaicin [39][14]
15,000,000 Dihydrocapsaicin [39]
9,200,000 Nonivamide [39]
9,100,000 Nordihydrocapsaicin [39][14]
8,600,000 Homocapsaicin, Homodihydrocapsaicin [39]
160,000 Shogaol [40]
100,000 to 200,000 Piperine [41]
60,000 Gingerol [40]
16,000 Capsiate

References
  1. Some sources such as Guzman[4] state a factor of 16 in line with the 16,000,000 SHU figure of pure capsaicin. However, Guzman cites the collins source[5] which clearly states 15 per ASTA.
  2. Estimate; too strong to be used in human taste-testing.
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  11. Tainter, Donna R.; Anthony T. Grenis (2001). Spices and Seasonings. Wiley-IEEE. p. 30. ISBN 978-0-471-35575-5. Interlab variation [for the original Scoville scale] could be as high as +/−50%. However, labs that run these procedures could generate reasonably repeatable results.
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  21. "Red Pepper Spray Ingredients and Formula". sabrered.com. SABRE - Security Equipment Corp. Sabre Red=10% OC @ 2,000,000 Scoville Heat Units. Thus, 90% of the formulation dilutes the 2,000,000 SHUs creating a Scoville Content of 200,000.
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