Bananas will brown sooner in the summertime than in the winter, and for a good reason. Heat hastens the ripening process. That is why bananas are shipped when they're green, at a temperature of 58 degrees Fahrenheit, so they do not ripen quickly. Under normal circumstances, yellow bananas will quickly brown, inside and out, giving them perhaps a two-day range of freshness. There is a way, though, to keep bananas fresh for a couple days longer.
Buy bananas with a yellow portion of about 75 percent. It should have some green on both ends with no blemishes.
Store the bananas on a kitchen counter or a hanging rack. Optimally, the room temperature should be no higher than 75 degrees Fahrenheit; temperatures higher than that will hasten ripening.
Place the bananas in the refrigerator once they are completely yellow. The skin will brown, and may even turn black. However, the fruit inside will remain white for up to four days longer than if the fruit was left in room temperature. Skin and freeze the bananas if you want to keep them longer than four days. Place the bananas in plastic zipper bags and they should keep for months.