Posted: 12/08/2013 at 12:52
I think part of the problem may well be that they are in the greenhouse-sounds strange but despite being tropical, chilli plants have a temperature limit of around 30 degrees- "too hot, they rot". I think excessive heat and then the sharp temperature drop at night affects the plant's enzymes and stops full ripening occuring- they like a constant temperature.
Also, the air inside greenhouses is "still", chillis like humidity but with ventalation, otherwise Botrytis (grey mold) can occur on stems, petioles and fruits. Basically, they're fussy!
Traditionally, chillis are picked whilst still green- leaving until red reduces yeilds by up to 25%. Pick the all the older chilli's off, any rot will spread quickly in humid greenhouses and ruin all your hard work. Snip off the chillis and ripen on a windowsill (lodging chillis upright in an old egg carton sometimes works alon).
I always pick mine green once they have reached good size- the amount of capsaicin (heat) won't be much less at all- the chillis should ripen okay inside (and so sweeten as the natural storage carbohydrates convert into sugars).
Hope this helps and fingers crossed that they pick up-