It seems many popular pickling type peppers are picked in their unripe stage. I think sometimes it has to do with seed maturity not making good pickles. I also see Cubanelle's sold in the yellow stage, but personally I like them red, ripe and roasted
Actually AJ found a study being done by a bunch of PhD candidates that found capsaicin is at it's max around the 35--40 days of pod growth. Think that may only apply to chinense though.
If they didn't pick them while they're still yellow, they wouldn't look like bananas.
A guy at the Farmer's Market told me once that all peppers will turn red if you leave them on the plant long enough. I'd never heard that before. His thought on that was that different peppers taste best at various stages of maturity... or maybe that was just what I inferred. I'm usually too impatient to wait that long.
I've had red wax and greeks... those 2 in particular seem to get hotter as they mature past the normal unripe eating stage.
Jalapenos taste different red - similar to bell pepper ripening - but I can't tell one way or the other with the heat. I know the chemical change to red is supposed to decrease the heat a bit but it ain't by much. Well within the normal variation of peppers on the same plant. They're cool looking to mix in with a jar of the pickles though.
Jalapenos, and probably all chiles, get hotter as they ripen but I believe the heat peaks just before full maturity and then decreases quickly. There is also a higher percentage of sugar in the peppers when they are ripe, and definitely not all peppers ripen red
Potawie is right, as the pepper ripens flavor and sugar increases, heat increases but then platoes and starts dropping.
If I want heat and flavor, I pick right when they reach peak color and no longer. If I want less flavor, I pick them before they ripen all the way and freeze them to prevent them from ripening further. And some peppers have more than one color stage, they can be green to yellow to red, and you simply pick them when they reach the color you desire.