Bananas turn brown as they ripen and after they are cut. Ethylene gas produced by a ripening banana speeds up ripening, causing brown spots to appear on the peel and eventually spread. Peel discoloration and browning of the flesh are two different processes. Changes in peel pigments and ethylene contribute to darkening as the fruit ripens. When the flesh is cut, enzymes react with oxygen in the air, much like they do in cut apples or avocados. Warm conditions speed up browning, and bruised areas can darken sooner because their cells have been damaged.
How to slow banana browning
You cannot stop browning completely, but proper storage and preparation can slow it:
• Store bananas in a cool, shaded place away from other fruit.
• Wrapping the stem of the bunch in plastic wrap may reduce the ethylene released.
• Drizzle a few drops of lemon juice over sliced bananas to slow enzymatic browning.
• Very ripe bananas can be refrigerated with the peel on. The peel may darken, while the flesh can remain usable for a while longer.
• Avoid stacking heavy items on bananas, which can bruise them.
Common storage mistakes
Storing bananas with ethylene-producing fruits such as apples and pears can speed up ripening. A hot, sunny countertop also encourages browning. Refrigerating unripe bananas may slow or stop ripening, so let them ripen at room temperature first. Leaving sliced bananas exposed to air for a long time speeds browning.
Does refrigeration prevent browning?
The peel of a ripe banana may darken quickly in the refrigerator, but that alone does not mean the flesh has spoiled. The flesh may remain fresh and edible for a while longer. Refrigerating an unripe banana can interrupt ripening, so let it ripen at room temperature before chilling it if needed.
Can you use browned bananas?
A spotted or dark peel and soft flesh do not necessarily mean a banana is spoiled; very ripe bananas are sweeter and work well in cakes, banana bread, and smoothies. Discard bananas with mold, a sour smell, or leaking flesh. Using ripe bananas in baked goods can prevent waste and add natural sweetness.
Ethylene and enzymatic browning explain why bananas darken. Keep them cool and away from other ripening fruit, and use lemon juice on cut pieces to slow browning. Very ripe bananas can be used in baking when they show no signs of spoilage.