Capsaicin

[AndrewB]

Another possible variation:  when does the heat appear?  I've recently read of two kinds that change
while ripening.

One develops its heat when it ripens to red - can't remember its name.

and, just the opposite:  Aji escabeche, a baccatum from Peru, is hot while green but sweet
and mild once ripe.

Are there others?

Jalapenos are like that. Hot when green,  mild when red. The red ones taste sooo good pickled with a grape vine leaf to make them crunchy!!