The optimum temperature for ripening tomatoes is 70 to 75F. If the temperature rises to 85 to 90F, the ripening process slows drastically or even stops. In addition, the pigments that give tomatoes their orange to red hue, such as lycopene and carotene, cannot be produced in these higher temperatures, causing the fruit to remain in a mature green state for an extended period of time, according to the Cornell Vegetable Program.