Scoville unit

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

The hot in peppers comes from a substance called capsaicin and closely related compounds. 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 grinding up a measured mass of the pepper and mixing it with ethanol. The ethanol dissolves the capsaicin. The alcohol solution is then diluted with sweetened water until a human taster can no longer detect any pungency. The degree of dilution required indicates the pungency of the pepper and the rating in 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This dilution test has been replaced by one using a high pressure liquid chromatograph,² the results of which are often expressed in ASTA units (named for the American Spice Trade Association), but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. Scoville, Wilbur L. 1912.
Note Capsicum.
Journal of the American Pharmaceutical Association, volume 1, page 453.

2. Woodbury, J.E. 1980.
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.

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

Chili pepper lovers maintain a ring of fine Web sites; a good entry point is easyweb.easynet.co.uk/~gcaselton/chile/chile.html

If you're interested in growing peppers, a nursery site at www.chileplants.com.

For Further Reading

Amal Naj.
Peppers. A Story of Hot Pursuits.
New York: Knopf, 1992.

Richard Schweid.
Hot Peppers. The Story of Cajuns and Capsicum. Revised Edition.
Chapel Hill, NC: Univ. of North Carolina Press, 1999.