With its rich, sweet banana flavor, banana bread is more like a baked dessert than traditional bread. Highly ripe bananas give this beloved sweet bread its strong banana flavor and signature moistness. However, that moistness is the very thing that makes banana bread highly perishable. Mold loves moisture and grows faster in moisture-rich baked goods. Even if you cannot see it on the surface, mold could be spreading inside of the banana bread, especially if it's been sitting out for a while. Check for visible signs of mold and consider how you stored your banana bread before you take another slice.
Look for visible signs of mold. The most obvious sign that the banana bread has spoiled is mold on the surface of the loaf. Fuzzy white or green mold, sometimes with other colors, may be present. Discard immediately and wash the loaf pan thoroughly in hot soapy water . Even if you cannot see mold on the surface, mold could still be growing inside the banana bread, so you may want to slice into the center of the loaf as well.
Consider how you stored the banana bread. Banana bread should not be left out on the counter for more than two days because most room temperatures are ideal for mold and bacteria growth. If you placed the banana bread in the fridge, it should be thrown away after a week. If you placed it well wrapped in the freezer, banana bread can last up to three months. While mold will not grow in freezing temperatures, keep in mind that the quality and flavor will have degraded the longer you keep it in the freezer.
Smell for a strong odor. Banana bread that has gone bad if left sitting out on a counter, especially if the temperature has been warm, may have an even stronger banana smell, or may give off a somewhat sour dairy smell. If the smell is particularly strong when you are close to it or when you unwrap it, toss it out. Do not stick your nose right up to the banana bread to sniff, however, because you could wind up sniffing up toxic mold spores, which can cause respiratory problems, according to the U.S. Department of Agriculture.
Follow the "When In Doubt" rule. If you can't remember how long you've left the banana bread out, or something just doesn't seem right, even if it looks fine, don't take the risk of ingesting toxic mold by eating it anyway.. Remember the saying "when in doubt, throw it out," and save yourself -- and your stomach -- the hassle.