Aluminum foil or plastic wrap will create an airtight seal around the stems, trapping ethylene gas and preventing it from circulating into the air.
Don't make the same mistake I did and use baking paper: I've found that it doesn't work because it doesn't form a good seal to keep out the ethylene gas.
About two weeks ago, I tried this method with a bunch of bananas I'd just bought, and after 10 days, they were still fresh. With just a little foil, they lasted almost two weeks longer than in a fruit basket.
I've also learned that it's better to leave bananas on the bunch than to separate them. For example, I recently noticed that a banana I accidentally removed from the bunch developed spots, while the other bananas, still on the bunch, looked perfectly fine.
Another tip I found online is that you can store bananas in the refrigerator to slow the ripening process. The cold significantly slows spoilage, so I tried putting the blemished bananas in the refrigerator for lunch. Five days later, they were still yellow and perfectly edible.
Properly storing bananas is surprisingly simple, and I'm amazed at how much money I've wasted by not doing the research first!
