Wouldn't you know it. The day you decide to bake a banana pudding, all the local market has is green bananas . While I can't tell you how to get them to ripen by dinner time, I can tell you how to ripen bananas quickly:
These bananas are ripening on the plant at Selby Gardens in Sarasota, FL.
Get a brown paper bag big enough to close once the fruit is in it.
Place the bananas inside the bag.
Put another piece of fruit in the bag with the bananas. This could be an apple, pear, peach, etc. Any hard fruit. You wouldn't want to use berries as whatever you put inside the bag is going to ripen more quickly itself and berries are too perishable.
Fold the top of the bag down and set it in a warm room temp location. The top of the fridge will do.
Don't forget the bananas are up there or you'll end up with a kitchen full of knats.
Check the bananas in a couple of days. Once the bananas begin to ripen, check them more frequently. It doesn't take long for bananas to go from ripe to overripe.
How To Keep Bananas Fresh
This is the flip side of how to ripen bananas.
To keep bananas fresh longer, store them by themselves. All fruit emits a gas that hastens the ripening process. This is why the brown bag technique works so well. Putting the fruit into an enclosed environment magnifies the effect of the gas.
The bananas will stay fresh longer if air can circulate all around them. This is why those cute wooden banana hangers are so popular. Storing bananas in any kind of bag is a bad idea. Unless you're trying to ripen them. If you can't hang them and you don't want to just leave them laying on the table; you could put them in a colander.
Even with careful storage, bananas will only keep for a few days before becoming overripe. If you want to hold them at the peak of ripeness, there are two things you can do:
Put them in the fridge.
When you refrigerate bananas the skin will turn black. This makes the bananas look like they're rotten. They're not. The flesh will stay fresh for a few days longer than it would have at room temperature.
If you want to keep them longer than this, you'll have to freeze them.