To keep a bunch of bananas fresh for longer, wrap the stems in some plastic wrap. Re-cover the bananas with the wrap after removing one. This method prevents ethylene gas, produced naturally in the ripening process, from reaching other parts of the fruit and prematurely ripening it.
Wrap the stems of the bananas in plastic wrap. This will prevent ethylene gas, which is produced naturally during the ripening process, from reaching other parts of the fruit and making it ripen too fast. You can even place some tape over the plastic wrap for some extra security. Every time you remove a banana from the bunch, rewrap it carefully. Alternately, you can just separate the bananas from the bunch and then wrap the stem of each one individually.