The general rule for making banana bread, or other banana-based treats like banana cake or banana cupcakes that you should always keep in mind is: the riper the bananas, the better; the browner and grosser looking the bananas, the sweeter. Really! You’ll know that your bananas are ready for baking when they are very soft to touch and their skins are brown all over.
The easiest way to ripen bananas is usually naturally done; we’ve all bought too many bananas at the grocery store and haven’t eaten them all in time, letting them sit and spot on our counters. (Pro tip: It usually takes bananas about 24 to 48 hours to ripen naturally on the counter. And if you keep them all in a bunch, they should ripen at the same rate.) But if you have green bananas and need banana bread, like, now, accelerating the ripening process is possible!
In a paper bag: Bananas emit an aging hormone called ethylene, which is a small hydrocarbon gas. Ethylene is what changes the texture, softening and color in a selection of fruits, including apples and pears, which all cue a fruit’s ripeness. Store bananas in a paper bag on the counter, and the ethylene will circulate, speeding up the natural ripening process in about half the time, or 12 to 24 hours.
In the oven: For when you want brown bananas almost immediately, you can place them, peels-on, on a baking sheet and bake at 300°F for about 30 to 50 minutes. You’ll know they are done when they have turned shiny and black.