Banana bread and muffins need very ripe bananas for the best results. Not only are they naturally sweeter, but they're also soft, so they combine easily with the other ingredients. Banana bread made with underripe bananas lacks that "banana bread" flavour we love! However, bananas can become too ripe for baking. If your overripe bananas show any signs of mold or if they smell like they have fermented, it may be time to add them to your compost. Toss them out if they show signs of leaking fluid, too.