The Scoville scale is a measure of how pungent or spicy hot chili peppers and other chemicals are. Do you know how the scale is determined and what it means?

Origin of the Scoville Scale

The Scoville scale is named for American pharmacist Wilbur Scoville, who devised the Scoville Organoleptic Test in 1912 to measure the amount of capsaicin in hot peppers. Capsaicin is the chemical responsible for most of the spicy heat of peppers and certain other foods.

How to Measure Scoville

To perform the Scoville Organoleptic Test, an alcohol extract of capsaicin oil from a dried pepper is mixed with a solution of water and sugar to the point where a panel of taste-testers can barely detect the heat of the pepper. The pepper is assigned Scoville units based on how much the oil was diluted with water in order to reach this point. As an example, if a pepper has a Scoville rating of 50,000, that means capsaicin oil from that pepper was diluted 50,000 times before the testers could just barely detect the heat. The higher the Scoville rating, the hotter the pepper. Tasters on the panel taste one sample per session so that the results from one sample don't interfere with subsequent testing. Even so, the test is subjective because it relies on human taste, so it is inherently imprecise. Scoville ratings for peppers also change according to a type of pepper's growing conditions (especially humidity and soil), maturity, seed lineage, and other factors. The Scoville rating for a type of pepper may vary naturally by a factor of 10 or more.

Scoville Scale and Chemicals

The hottest hot pepper on the Scoville scale is the Carolina Reaper, with a Scoville rating of 2.2 million Scoville units, followed by the Trinidad Moruga Scorpion pepper, with a Scoville rating of around 1.6 million Scoville units (compared with 16 million Scoville units for pure capsaicin). Other extremely hot and pungent peppers include the Naga Jolokia or Bhut Jolokia and its cultivars, the Ghost chili, and Dorset Naga. However, other plants produce spicy hot chemicals that can be measured using the Scoville scale, including piperine from black pepper and gingerol from ginger. The 'hottest' chemical is resiniferatoxin, which comes from a species of resin spurge, a cactus-like plant found in Morocco. Resiniferatoxin has a Scoville rating a thousand times hotter than pure capsaicin from hot peppers, or over 16 billion Scoville units!

ASTA Pungency Units

Because the Scoville test is subjective, the American Spice Trade Association (ASTA) uses high-performance liquid chromatography (HPLC) to accurately measure the concentration of spice-producing chemicals. The value is expressed in ASTA Pungency Units, where different chemicals are mathematically weighted according to their capacity to produce a sensation of heat. The conversion for ASTA Pungency Units to Scoville heat units is that ASTA pungency units are multiplied by 15 to give equivalent Scoville units (1 ASTA pungency unit = 15 Scoville units). Even though HPLC gives an accurate measurement of the chemical concentration, the conversion to Scoville units is a little off, since converting ASTA Pungency Units to Scoville Units yields a value from 20 to 50 percent lower than the value from the original Scoville Organoleptic Test.

Scoville Scale for Peppers