The number of Scoville heat units (SHU) indicates the amount of capsaicin present. Capsaicin is a chemical compound that stimulates chemoreceptor nerve endings in the skin, especially the mucous membranes.
The scale is named after its creator, American pharmacist Wilbur Scoville. His method, devised in 1912, is known as the Scoville Organoleptic Test. The modern commonplace method for quantitative analysis uses high-performance liquid chromatography, making it possible to directly measure capsaicinoid content.
Scoville organoleptic test 
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 taste only one sample per session. Results vary widely, up to 50%, between laboratories.
High-performance liquid chromatography 
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. 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.
List of Scoville ratings 
Scoville ratings of chemicals 
|Scoville heat units||Examples|
Scoville ratings of peppers 
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 "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.
The Scoville scale may be extrapolated to express the pungency of substances that are even hotter than pure capsaicin. 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.
- The pungency is diluted to 200,000 or fewer SHU.
- Peter, KV, ed. (2001), Handbook of Herbs and Spices 1, CRC Press, p. 120, ISBN 0-8493-1217-5.
- The Journal of the American Pharmacists Association 1, 1912: 453–4.
- Bosland, Paul W.; Walker, Stephanie J. (February 2010). "Measuring Chile Pepper Heat". aces.nmsu.edu. New Mexico State University Cooperative Extension Service, Guide H-237. Retrieved August 21, 2012.
- Tainter, Donna R.; Anthony T. Grenis (2001). Spices and Seasonings. Wiley-IEEE. p. 30. ISBN 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."
- DeWitt, Dave; Bosland, Paul W. (2009). The Complete Chile Pepper Book. ISBN 978-0-88192-920-1.
- "Chemical hazards in law enforcement". The Police Policy Studies Council. Retrieved 2009-02-09. "Most law enforcement sprays have a pungency of 500,000 to 2 million SHU. One brand has sprays with 5.3 million SHU."
- "The Truth About Defensive Spray Heat". Sabre red. "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."
- "Chile experts identify Trinidad Moruga Scorpion as world's hottest". UK: The Daily Telegraph. 2012-02-16.
- Dykes, Brett Michael (3 December 2010). "World’s hottest pepper is ‘hot enough to strip paint’". Yahoo! News. Retrieved 3 December 2010.
- "Grantham's Infinity chilli named hottest in world". News (BBC). 2011-02-18.
- Shaline L. Lopez (2007). "NMSU is home to the world's hottest chile pepper". Archived from the original on 2007-02-19. Retrieved 2007-02-21.
- AP (23 February 2007). "World's hottest chili pepper a mouthful for prof". CNN. Archived from the original on 2007-03-22.
- Matthew Da Silva, "Aussies grow world's hottest chilli", Australian Geographic, 12 April 2011
- "UK’s hottest commercially grown chilli pepper goes on sale".
- "World's hottest chile pepper discovered". American Society for Horticultural Science. Retrieved 2008-03-31.
- "Chile Pepper Heat Scoville Scale". About. Retrieved 2006-09-25.
- "Habanero White". Chile man. Retrieved Sep 21, 2011.
- "The Scoville Scale". Happy stove.
- Scoville Food Institute, Periodic Table of Scoville Units.
- "Scoville Scale Chart for Hot Sauce and Hot Peppers". Scott Roberts. Retrieved 2008-11-19.
- Scoville hot sauce heat scale, Hot sauce
- "Anaheim Pepper" (PDF). Chile Pepper Institute at New Mexico State University. 2007. Retrieved 2007-10-22.[dead link]
- "World’s hottest chilli grown in Grantham, Lincs". The Daily Telegraph (London). 2010-04-01. Retrieved 2010-04-24.
- "Grantham firm grows world's hottest chilli". UK: This is Lincolnshire. Retrieved 2010-04-24.
- Atala, Anthony; Slade, Debra (2003), Bladder Disease, Washington, DC: National Bladder Foundation, p. 361.