What heat scale is used to rate jalapeños, a pepper often used in guacamole?

The heat scale used to rate jalapeños is measured in Scoville heat units (SHU).

The Scoville scale was devised by American pharmacist Wilbur Scoville in 1912. His original test diluted pepper extract in sugar water until trained tasters could no longer detect heat. The number of dilution steps became the pepper’s Scoville rating.

Jalapeños usually measure about 4,000–8,500 SHU, although growing conditions, variety, ripeness, and preparation can change the result. Red, fully ripe jalapeños are often hotter than green ones, and peppers from the same plant can vary.

Scoville heat units describe pungency, not flavor. Capsaicin and related capsaicinoids create the burning sensation, especially in the pepper’s pale internal placenta. Modern laboratories commonly use high-performance liquid chromatography rather than the subjective tasting method.