Why Do Bananas Turn Brown?

Have you ever left a banana on the counter and come back to find it turning dark and soft? This is not magic; it is a chemical reaction. Inside every banana is a special helper called an enzyme. When you cut a banana or leave it out, air gets in. The air contains oxygen. The enzyme meets the oxygen, and they mix together to make a brown color. It is like when you cut an apple and it turns brown too.

Bananas have a natural way to protect themselves. The enzyme is called polyphenol oxidase. It works like a tiny factory. When the banana skin breaks, the factory opens up to the air. The oxygen from the air mixes with the enzyme. They make a brown substance called melanin. This is the same stuff that colors your hair and skin.

Yes! If you squeeze lemon juice on a cut banana, the acid stops the enzyme from working. Cold temperatures also slow it down. So, a brown banana is just a banana that has met the air and started to change.