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Why Do Bananas Turn Brown?

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Ever wondered why your two-day-old bananas go brown? While the changing colors of a banana are a common enough phenomenon, most people do not know why this happens. When a banana grows it forms a thick green skin and as it ages, the skin changes from green to yellow. When the banana is yellow, it is at its ripest best. From here on, the banana will only turn brown.

Stages in the Life of a Banana

As the banana over-ripens, the peel develops dark spots, and the banana itself becomes soft. The peel eventually turns dark brown or even black. The question is, why does this happen?

What Happens

According to the experts, bananas contain an enzyme called polyphenol oxidase, also called tyrosinase. This enzyme reacts with the oxygen present in the air and this makes the banana turn brown. Some compare this reaction to the formation of rust. In fact, rusting and bananas turning brown are almost the same chemical reaction. The basic materials of the banana react to the oxygen in the air and turn brown, just like the iron in the metal reacts to the oxygen.


The best way to prevent bananas from turning brown is to keep them away from oxygen. But since oxygen is everywhere, the next best thing to do is sprinkle the banana with some acidic juice, such as lemon juice. The juice helps deactivate the enzyme so that it does not react with the air. 

You can also get yourself some commercial preservatives to stop the bananas from turning brown.

It is, however, important to note that any fruit will turn brown when left in contact with the air. This is a natural process, and perhaps a reminder that you must eat the fruit while it is ripe and before it begins to get spoilt!

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Why Do Bananas Turn Brown?