Most shoppers will look for bananas that are slightly green, firm and without bruises. The fruit should never be stored in the chiller because the cold interferes with the ripening process - if bananas have a grey tinge and a dull appearance, they've been refrigerated, and bringing them back to room temperature will not reverse the process.
Once ripe, bananas can be refrigerated for up to two weeks, but their skins will turn black. Yellow-green bananas should be given time to ripen at room temperature to a sunny yellow colour - from one to three days - or they will taste astringent.
Most fruits give off an ethylene gas during ripening and because bananas release a higher concentration of ethylene, they ripen quickly. But green bananas can be ripened quicker by being stored in a paper or plastic bag, and adding an apple to the bag will encourage even faster ripening.