It can take between one to two days for bananas to ripen. If the bananas are too green to eat, then placing them in a brown paper bag with an apple overnight will speed up the ripening process.
Most people tend to buy yellow bananas that are not too ripe. However, to keep them from ripening quickly, it is important to store them properly. Bananas should be taken out of the plastic wrap and left at room temperature in the kitchen. They should not be placed in the refrigerator, especially if they are unripe, because this will interrupt the ripening process.
The ripening process for bananas occurs gradually, in stages. Bananas are green in color at the beginning of the process and turn bright yellow, then yellow with brown specks and finally black. Depending on how ripe they are, fresh bananas can last between two to seven days on a countertop.