Scoville Units (SHU) are used to measure the “heat,” strength, or bite of pepper spray and also different types of hot peppers. If you’re a careful pepper spray consumer, or you enjoy eating lots of hot peppers, you might be wondering how Scoville Units were developed and what they mean. Here’s an intro to Scoville Units for those with a not-so-scientific brain.
American pharmacist Wilbur L. Scoville developed Scoville Units in 1912 as a method for measuring the spiciness of hot peppers. Scoville’s original method was called the Scoville Organoleptic Test. This test involved soaking different types of peppers in alcohol overnight to extract their capsaicin, the chemical compound in peppers that causes their spiciness. After extracting the capsaicin in alcohol, Scoville incrementally added sweetened water and repeatedly tasted the solution.
Scoville gave each pepper a reading when he had added enough sweetened water that the pepper’s spiciness was barely detectable. The number each pepper received referred to the number of times Scoville diluted the capsaicin extract in order for its spiciness to be undetectable. On Scoville’s scale, for example, a bell pepper would receive a rating of 0 because dilution was not required. A Japanese chili, however, would receive 20,000 because the pepper extract would have to be diluted 20,000 times to eliminate spiciness.
Today, high performance liquid chromatography (HPLC) has generally replaced Scoville’s Organoleptic Test. Using HPLC, a pepper’s spiciness is measured in terms of the concentration of capsaicin and ranked according to its relative ability to produce a heat sensation. American Spice Trade Association (ASTA) pungency units are usually used with this method. One ASTA unit is equivalent to about 15 Scoville units.
Here’s a ranking of common peppers, and pepper spray, on the Scoville scale:
0: Sweet Bell Peppers
500-750: Red Chiles
500-2,000: Anaheim Chiles
1,000-2,000: Pablano Chiles
1,500-2,500: Chilaca Chiles
2,500-4,000: Guajillo Chiles
3,500-8,000: Jalapeno Peppers
5,000-8,000: Yellow Hot Chiles
8,000-23,000: Serrano Chiles
12,000-30,000: Manzano Chiles
15,000-30,000: Arbol Chiles
30,000-50,000: Cayenne Chiles
100,000-250,000: Chiltepin Chiles
200,000-350,000: Habanero Chiles
350,000-580,000: Red Savina Chiles
855,000-1,463,700: Bhut Jolokia Chiles
2,000,000-5,300,000: U.S. Pepper Spray
15,000,000: Pure Capsaicin