For the uninitiated, a chile pepper is either hot or not, but actually each pepper can produce a different kind of heat depending on its variety. The Scoville scale assigns a number to the pepper depending on how spicy it is, and one factor to determine this number is whether the heat the pepper produces is sharp or flat. What does "flat heat" actually mean?
A Chile Pepper's Flat Heat, Defined
If you bite into a hot chile pepper and the heat coats your entire tongue and just won't go anywhere, then what you are feeling is flat heat. It's as if that spicy sensation was painting on your tongue — it's a sustained burn, often getting worst at it lingers. This type of heat is more common in American — be it Central, South, or North — varieties of chile peppers, like Mexican habaneros and jalapeños, and Peruvian aji amarillos.
Read More: What Is Sharp Heat?