The spicy or heat of a chile depends on seven closely related alkaloids or capsaicinoids.
In the early 1900s, Wilbur L. Scoville invented a test to determine the relative spice of various chilies.
Capsaicin of a chile of a certain weight was extracted with alcohol and mixed in several concentrations with sweetened water.
Human testers were asked to determine at what point hot spicy.
The volume of water required for each sample was assigned a rating in Scoville units. The larger the number, the more water was needed and the chili was more spicy. A high pressure liquid chromatography examination replaced this technique in the early 1980s, but measurements are still expressed in Scoville units.
The following chiles are listed from the most spicy to the least spicy, according to Scoville units.
Red Caribbean _100,000,445,000
Red _ 80,000,285,000 Scotch Bonnet_ 80,000,260,000