Scoville unit

A unit used to express the pungency of peppers, introduced by a pharmacist, W. L. Scoville, in 1912.¹ Also called the Scoville heat unit. Symbol, SHU.

The heat in peppers comes from substances called capsaicinoids, principally (95%) from capsaicin and dihydrocapsaicin. Capsaicin does not dissolve in water, but it does dissolve in alcohol and fats. Thus milk, with lots of butterfat, will relieve a burning mouth and a glass of water will not.

The Scoville unit rating for a pepper was originally determined by mixing 1 grain of ground pepper with 100 milliliters of ethanol. The ethanol dissolves the capsaicin. After sitting overnight the solution is shaken and filtered. It is then diluted with sweetened water until a human taster can barely detect any pungency. The degree of dilution required indicates the pungency of the pepper and the rating in Scoville units. For example, if the tester can barely detect any heat in a mixture of 1 part of the alcohol solution in 50,000 parts of sweetened water, the pepper is rated at 50,000 Scoville units.

This dilution test has been replaced by one using a high pressure liquid chromatograph,² the results of which are often expressed in ASTA units (named for the American Spice Trade Association), but can also be expressed in Scoville Heat units. The chromatograph can determine the concentration of capsaicin and capsaicin-like compounds in the pepper in parts per million. To convert from ppm capsaicin to SHU, multiply by 16, because pure capsaicin has a pungency of about 16 million Scoville units. (An older convention multiplied by 15.) Thus a ground-up pepper that is 1000 ppm capsaicin and capsaicin-like compounds will have a pungency rating of 16,000 SHU.

Type of Pepper Pungency in Scoville units
bell peppers, pimentos 0
long green Anaheim 250 – 1,400
poblano 3,000
Hungarian yellow 4,000
jalapeño 3,500 – 4,500
serrano 7,000 – 25,000
chile de arbol 15,000 – 30,000
tabasco 30,000 – 50,000
santaka (Japan) 50,000-60,000
Mexican tabiche 100,000
cayenne 100,000 – 105,000
birdseye (India) 100,000 – 125,000
kumataka (Japan) 125,000 – 150,000
habanero 300,000
Red Savina habanero 577,000
bhut jolokia 1,001,304

Breeders are still trying to develop even hotter peppers, but there is an upper limit to the scale: 16,000,000, the pungency of pure capsaicin.

The search for ways of describing the hotness of peppers is quite old. Nahuatl, the language of the Aztecs, has six adjectives describing the hotness of peppers. In order of increasing pungency, they are: coco, cocopatic, cocopetz-patic, cocopetztic, copetzquauitl, and cocopalatic.

1. Wilbur L. Scoville.
Note on Capsicums.
Journal of the American Pharmaceutical Association, volume 1, page 453 (1912).

We provide Scoville's paper as a pdf file.

2. J. E. Woodbury.
Determination of Capsicum pungency by high pressure liquid chromatography and spectrofluorometric detection.
Journal of the Association of Official Analytical Chemists, volume 63, pages 556-558 (1980).

M. M. Wall and P.W. Bosland.
Analytical methods for color and pungency of chiles (capsicums).
Instrumental Methods in Food and Beverage Analysis. [issue title]
Developments in Food Science, vol. 39, pages 347-373 (1998).

A review of current methods by authorities at New Mexico State University.

on the web

New Mexico State University's Chile Pepper Institute has an excellent website at http://spectre.nmsu.edu/dept/welcome.html?t=CHILE 

sources

1

Most pepper sprays available to the public are between ½-million and 2-million Scovile heat units, the measure of a chili pepper's “hotness.” These nonblistering, point-and-spray formulas are refined to 5.3 million Scoville units.

Advertisement for pepper spray, Sportsmans Guide catalog, 2010.

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