The best way to store bananas is simply to keep them at room temperature. Depending on how ripe the bananas are at the time of purchase, they should last for three to about six days. Do not store bananas in the refrigerator; there, the ripening process stops, and the peels turn an unappealing shade of brown.
While there exist many claims that different storage methods can speed up or slow down the ripening process, these methods are mostly ineffective. Cooking site TheKitchn conducted an experiment that used three different groups of bananas: one group was kept in a bunch, one group was separated and the third group was separated and had their stems wrapped with plastic wrap. The bunch of bananas ripened slightly more slowly than the other two groups, but the difference was negligible.
It is also possible to freeze bananas. Choose fruit that is already the ideal level of ripeness, as ripening stops when the fruit is frozen. Do not freeze whole bananas, because they turn rock hard and impossible to peel.
Cut peeled bananas into slices, and arrange them in a single layer on a baking sheet covered with parchment paper. Cover the slices with plastic wrap, and freeze the sheet until the slices are frozen, about one hour. Transfer the slices to plastic freezer bags or freezer containers. Use the bananas within six months.