The Scoville scale is a measurement

Measurement

Measurement is the process or the result of determining the ratio of a physical quantity, such as a length, time, temperature etc., to a unit of measurement, such as the metre, second or degree Celsius...

 of the spicy

Spice

A spice is a dried seed, fruit, root, bark, or vegetative substance used in nutritionally insignificant quantities as a food additive for flavor, color, or as a preservative that kills harmful bacteria or prevents their growth. It may be used to flavour a dish or to hide other flavours...

 heat

Heat

In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

 (or piquance

Piquance

Piquance is a sensation associated with the sense of taste. In various Asian countries it has traditionally been considered a basic taste.-Etymology:...

) of a chili pepper

Chili pepper

Chili pepper is the fruit of plants from the genus Capsicum, members of the nightshade family, Solanaceae. The term in British English and in Australia, New Zealand, India, Malaysia and other Asian countries is just chilli without pepper.Chili peppers originated in the Americas...

. The number of Scoville heat units (SHU) indicates the amount of capsaicin

Capsaicin

Capsaicin 2CHCH=CH4CONHCH2C6H3-4--3- ) is the active component of chili peppers, which are plants belonging to the genus Capsicum. It is an irritant for mammals, including humans, and produces a sensation of burning in any tissue with which it comes into contact...

 present. Capsaicin is a chemical compound

Chemical compound

A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 that stimulates chemoreceptor nerve endings in the skin

Skin

-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...

, especially the mucous membranes.

The scale is named after its creator, American pharmacist Wilbur Scoville

Wilbur Scoville

Wilbur Lincoln Scoville was an American pharmacist and is best known for his creation of "The Scoville Organoleptic Test", now standardized as the Scoville scale. He devised the test and scale in 1912 while working at the Parke-Davis pharmaceutical company to measure piquancy, or "hotness", of...

. His method, devised in 1912, is known as the Scoville Organoleptic Test. The modern commonplace method for quantitative analysis

Quantitative analysis (chemistry)

In chemistry, quantitative analysis is the determination of the absolute or relative abundance of one, several or all particular substance present in a sample....

 uses high-performance liquid chromatography

High-performance liquid chromatography

High-performance liquid chromatography , HPLC, is a chromatographic technique that can separate a mixture of compounds and is used in biochemistry and analytical chemistry to identify, quantify and purify the individual components of the mixture.HPLC typically utilizes different types of stationary...

, making it possible to directly measure capsaicinoid content.

Scoville organoleptic test

In Scoville's method, an alcohol extract of the capsaicin oil from a measured amount of dried pepper is added incrementally to a solution of sugar in water until the "heat" is just 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 that 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.

High-performance liquid chromatography

Spice heat is usually measured by a method that uses high performance liquid chromatography

High performance liquid chromatography

High-performance liquid chromatography , HPLC, is a chromatographic technique that can separate a mixture of compounds and is used in biochemistry and analytical chemistry to identify, quantify and purify the individual components of the mixture.HPLC typically utilizes different types of stationary...

 (HPLC). This identifies and measures the concentration of heat-producing chemicals. The measurements are used in a mathematical formula that weights 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. Results vary widely, up to 50%, between laboratories.

List of Scoville ratings

Scoville heat units	Examples
	Pure capsaicin Capsaicin Capsaicin 2CHCH=CH4CONHCH2C6H3-4--3- ) is the active component of chili peppers, which are plants belonging to the genus Capsicum. It is an irritant for mammals, including humans, and produces a sensation of burning in any tissue with which it comes into contact...
8,600,000–9,100,000	Bear spray, various capsaicinoids (e.g., homocapsaicin Homocapsaicin Homocapsaicin is a capsaicinoid and analog and congener of capsaicin in chili peppers . Like capsaicin it is an irritant. Homocapsaicin accounts for about 1% of the total capsaicinoids mixture and has about half the pungency of capsaicin. Pure homocapsaicin is a lipophilic colorless odorless... , homodihydrocapsaicin Homodihydrocapsaicin Homodihydrocapsaicin is a capsaicinoid and analog and congener of capsaicin in chili peppers . Like capsaicin it is an irritant. Homodihydrocapsaicin accounts for about 1% of the total capsaicinoids mixture and has about half the pungency of capsaicin. Pure homodihydrocapsaicin is a lipophilic... , nordihydrocapsaicin Nordihydrocapsaicin Nordihydrocapsaicin is a capsaicinoid and analog and congener of capsaicin in chili peppers .- Properties :Like capsaicin, it is an irritant. Nordihydrocapsaicin accounts for about 7% of the total capsaicinoids mixture and has about half the pungency of capsaicin. Pure nordihydrocapsaicin is a... )
500,000–2,000,000	Most Law enforcement grade pepper spray Pepper spray Pepper spray, also known as OC spray , OC gas, and capsicum spray, is a lachrymatory agent that is used in riot control, crowd control and personal self-defense, including defense against dogs and bears...  (however it is diluted to 100,000 - 200,000),
855,000–1,463,700	Naga Viper pepper Naga Viper pepper The Naga Viper pepper was the official holder of the Guinness World Records "World's Hottest Chilli" record as of February 25, 2011. The Naga Viper pepper, with its rating of 1,382,118 Scoville Heat Units , beat the previous record holder, the Infinity Chilli... , Infinity Chilli Infinity chilli The Infinity Chilli pepper is a chili pepper created in England by chili breeder Nick Woods of Fire Foods, Grantham, Lincolnshire.For two weeks in February 2011, the Infinity Chilli held the Guinness World Record title for the world's hottest chilli with a Scoville scale rating of 1,067,286... , Bhut Jolokia chili pepper, Trinidad Scorpion Butch T pepper Trinidad Scorpion Butch T pepper Trinidad Scorpion Butch T pepper is a chili pepper that has been measured as the world's hottest. The pepper is a particular strain of the Trinidad Scorpion . It is named after Butch Taylor, the owner of a hot sauce company who is responsible for propagating the pepper's seeds...
350,000–580,000	Red Savina habanero Red Savina pepper The Red Savina pepper is a cultivar of the habanero chili , which has been selectively bred to produce hotter, heavier, and larger fruit....
100,000–350,000	Habanero chili, Scotch bonnet pepper, Datil pepper Datil pepper The Datil is an exceptionally hot pepper, a variety of the species Capsicum chinense .Datils are similar in strength to habaneros but have a sweeter, fruitier flavor. Their level of spiciness may be anywhere from 100,000 to 300,000 scoville units... , Rocoto Rocoto Capsicum pubescens is a species of the genus Capsicum , which is found primarily in Central and South America. The name component pubescens means hairy, which refers to the hairy leaves of this pepper. The plants, but especially the fruits, are often referred to as rocoto and locoto... , Madame Jeanette Madame Jeanette Madame Jeanette is a chili pepper originally from Suriname.The fruits are shaped like small bell peppers but with Habanero-like heat. The peppers ripen to reddish-yellow but they are larger and not symmetrical. When raw, the taste is of a hot burning, with a very tasty flavor... , Peruvian White Habanero, Jamaican hot pepper
50,000–100,000	Byadgi chilli Byadgi chilli Byadgi chilli is a famous variety of chilli mainly grown in the Indian state of Karnataka. It is named after the town of Byadgi which is located in the Haveri district of Karnataka. The business involving Byadgi chillis has the second largest turnover among all chilli varieties of India... , Bird's eye chili, Malagueta pepper Malagueta pepper Malagueta pepper, a kind of Capsicum frutescens, is a type of chilli used in Brazil, Portugal and Mozambique. It is heavily used in the Bahia state of Brazil . It apparently gets its name from the unrelated melegueta pepper from West Africa .It is a small, tapered, green pepper that turns red as it... , Chiltepin pepper Chiltepin pepper Capsicum annuum var. glabriusculum is a variety of Capsicum annuum that is native to southern North America and northern South America. Common names include chiltepin, chiltepe, and chile tepin. This variety is the most likely progenitor of the domesticated C. annuum var... , Piri piri (African bird's eye), Pequin pepper Pequin pepper Pequin pepper is a hot chile pepper, also known as "bird pepper", that is commonly used as a spice....
30,000–50,000	Guntur chilli Guntur Chilli Guntur chilies is a group of cultivars originating in Guntur District, Andhra Pradesh, India. They are exported to Asia, Canada, and Europe. The Guntur district is the main producer and exporter of most varieties of Chilies and chili powder in India to countries like Sri Lanka, Bangladesh, Middle... , Cayenne pepper Cayenne pepper The cayenne pepper—also known as the Guinea spice,cow-horn pepper, aleva, bird pepper,or, especially in its powdered form, red pepper—is a red, hot chili pepper used to flavor dishes and for medicinal purposes. Named for the city of Cayenne in French Guiana, it is a cultivar of Capsicum annuum... , Ají pepper Ají pepper Capsicum baccatum is a species of chili pepper that includes the following cultivar and varieties:*Aji amarillo, or amarillo chili*Peppadew*Lemon drop*Bishop's Crown*Brazilian Starfish*Wild Baccatum-Origins and distribution:The C... , Tabasco pepper Tabasco pepper The tabasco pepper is a variety of chili pepper species Capsicum frutescens. It is best known through its use in Tabasco sauce, followed by peppered vinegar.... , Cumari pepper (Capsicum Chinese)
10,000–23,000	Serrano pepper Serrano pepper The serrano pepper is a type of chili pepper that originated in the mountainous regions of the Mexican states of Puebla and Hidalgo. The name of the pepper is a reference to the mountains of these regions.... , Peter pepper, Aleppo pepper Aleppo pepper The Aleppo pepper in Turkish) is a variety of Capsicum annuum used as a spice, particularly in Middle Eastern and Mediterranean cuisine. Also known as the Halaby pepper, it starts as pods which ripen to a burgundy color and is then semi-dried, de-seeded, then crushed or coarsely ground...
3,500–8,000	Espelette pepper Espelette pepper The Espelette pepper is a variety of chili pepper that is cultivated in the French commune of Espelette, Pyrénées-Atlantiques, traditionally the northern territory of the Basque people... , Jalapeño pepper Jalapeño The jalapeño is a medium-sized chili pepper that has a warm, burning sensation when eaten. A mature jalapeño fruit is 2–3½ inches long and is commonly picked and consumed while still green, but occasionally it is allowed to fully ripen and turn crimson red... , Chipotle Chipotle A chipotle , or chilpotle, which comes from the Nahuatl word chilpoktli meaning "smoked chili pepper" is a smoke-dried jalapeño that tends to be brown and shriveled. It is a chili used primarily in Mexican and Mexican-inspired cuisines, such as Mexican-American and Tex-Mex.Varieties of jalapeño...  , Guajillo pepper, New Mexican New Mexico New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...  varieties of Anaheim pepper Anaheim pepper An Anaheim pepper is a mild variety of chili pepper. The name "Anaheim" derives from a farmer named Emilio Ortega who brought the seeds to the Anaheim, California, area in the early 1900s. They are also called California chili or Magdalena, and dried as chile seco del norte... , Hungarian wax pepper Hungarian wax pepper The Hungarian wax pepper is a medium variety of Capsicum annuum with a Scoville Scale range of 5,000 to 15,000 Scoville units.-Description:... , Tabasco sauce Tabasco sauce Tabasco sauce is the brand name for a hot sauce produced by US-based McIlhenny Company of Avery Island, Louisiana. Tabasco sauce is made from tabasco peppers , vinegar, and salt, and aged in white oak barrels for three years. It has a hot, spicy flavor...
1,000–2,500	Anaheim pepper Anaheim pepper An Anaheim pepper is a mild variety of chili pepper. The name "Anaheim" derives from a farmer named Emilio Ortega who brought the seeds to the Anaheim, California, area in the early 1900s. They are also called California chili or Magdalena, and dried as chile seco del norte... , Poblano pepper Poblano The poblano is a mild chili pepper originating in the State of Puebla, Mexico. Dried, it is called a chile ancho . The ripened red poblano is significantly hotter and more flavorful than the less ripe, green poblano. While poblanos tend to have a mild flavor, occasionally and unpredictably, they... , Rocotillo pepper Rocotillo Pepper A Rocotillo pepper is a type of chile pepper that originated in Peru. Unripe rocotillos are green or yellow, but the color at maturity varies. Common colors are red, orange or brown. Rocotillos are almost spherical in shape, and can be dried easily. They are generally an inch long and around an... , Peppadew Peppadew Peppadew is the brand name of sweet piquanté peppers grown in the Limpopo province of South Africa.-History:This type of piquante pepper was first discovered in early 1993 and introduced to market later that same decade...
100–900	Pimento Pimento A pimento or cherry pepper is a variety of large, red, heart-shaped chili pepper that measures 3 to 4 inches long and 2 to 3 inches wide . The flesh of the pimento is sweet, succulent and more aromatic than that of the red bell pepper... , Peperoncini, Banana pepper Banana pepper The banana pepper is a member of the chili pepper family. It is often pickled and used as an ingredient in sandwiches. It is a variety of the species Capsicum annuum. Its shape and color resembles a banana...
0	No significant heat, Bell pepper Bell pepper Bell pepper, also known as sweet pepper or a pepper and capsicum , is a cultivar group of the species Capsicum annuum . Cultivars of the plant produce fruits in different colors, including red, yellow, orange and green. Bell peppers are sometimes grouped with less pungent pepper varieties as... , Cubanelle Cubanelle The Cubanelle is a variety of sweet pepper of the species Capsicum annuum. When unripe, it is light yellowish-green in color, but will turn bright red if allowed to ripen. Compared to bell peppers it has thinner flesh, is longer, and has a slightly more wrinkled appearance... , Aji dulce Ají dulce Ají dulce is any of a variety of sweet perennial peppers found in Latin America and the Caribbean...

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 cultivar

Cultivar

A cultivar'Cultivar has two meanings as explained under Formal definition. When used in reference to a taxon, the word does not apply to an individual plant but to all those plants sharing the unique characteristics that define the cultivar. is a plant or group of plants selected for desirable...

s, 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, due 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

Resiniferatoxin

Resiniferatoxin is a naturally occurring, ultrapotent capsaicin analog that activates the vanilloid receptor in a subpopulation of primary afferent sensory neurons involved in nociception...

, 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.