[idlemind]

Sunshine is the other big variable. Most fruit will only get sweet during ripening if it's receiving enough sunlight. This is why red grapes are seldom grown in northern latitudes - their dark skin blocks sunlight and prevents them from sweetening during ripening.

[AfterShave]

Is it really about sunlight and not heat though? Otherwise one would expect to see more sweet fruit coming from northern europe than is the case. Given the near absence of "night."