The Scoville scale measures the hotness or piquancy of a chili pepper, as defined by the amount of capsaicin it contains. Capsaicin is a chemical compound which stimulates chemoreceptor nerve endings in the skin, especially the mucous membranes. The number of Scoville heat units (SHU) indicates the amount of capsaicin present.

The Scoville unit was named after Wilbur L. Scoville who first tried to measure the heat of peppers in 1912. Wilbur was a pharmacologist for the Parke-Davis Company.

His original test consisted of a panel of tasters who would systematically taste a solution of chile extract and slightly sweetened water for detectable heat. They tried to determine how much the chile extract needed to be diluted before it no longer had a detectable heat sensation.

A typical Jalapeno pepper is about 4,500 Scoville units. This means that 4,500 parts of sugar water are required to dilute one part Jalapeno extract until its heat can no longer be felt. Dilute it any further and you would not be able to taste any hotness.

As you can imagine, this testing method was highly subjective and is no longer used. However, chile heat is still given in Scoville units. Today, high-pressure liquid chromatography machines measure a pepper’s heat. Although this method takes out the guess work, it only rates the heat of the sample pepper being tested, and not the absolute fire power of every chile in that variety. Climate, soil, weather, geography and harvest time all affect how hot a pepper can be.