A chilli pepper hotness chart arranges the various known chilli peppers on an ascending or descending scale based on the measure of their "hotness," which is measured in units called "Scovilles." For example, a sweet bell pepper has a Scoville score of 0, whereas a habanero pepper measures approximately 300,000 Scovilles.
Capsaicin concentrations are the basis for the Scoville scale. Capsaicin is a chemical compound that produces the hot sensation associated with chilli pepper consumption. High capsaicin concentrations correlate to higher Scoville scores. Chilli peppers of the same variety can have different levels of capsaicin concentrations due to variance in growing conditions. Most peppers have a Scoville score range, instead of a single number, that estimates their level of heat. For example, the jalapeño pepper has a Scoville range of 2,500 to 5,000.
Chilli pepper varieties get their unique flavor and heat blends from their specific ratio of capsaicin and capsaicinoids. Capsaicinoids affect a chilli pepper's flavor, the duration of the heat sensation, and the timing of the heat. For example, habanero peppers have a delayed heat sensation due to capsaicinoids.
Wilbur L. Scoville, a pharmaceutical employee, developed the Scoville scale in 1912. Scoville initially measured capsaicin concentrations by systematically diluting the chilli pepper with sugar until a panel of five tasters could no longer detect any heat. The Scoville measurement unit actually represents the degree of dilution necessary to remove all traces of heat sensation from the chilli pepper.