Why do apples turn brown after you bite them?

Image by Alexas_Fotos from Pixabay

Question from Amy Ray

It’s all to do with the biological machines known as enzymes in the apple’s cells. When oxygen reaches injured plant tissue, enzymes called polyphenol oxidases whir into action. They start adding oxygen to some of the key flavour chemicals in apples, known as tannins. 

One more chemical reaction then makes new chemicals with the brown colour. The amount of this enzyme varies between apple species, and depends on how long the apple’s been growing, so some go brown faster than others. You can slow the process by avoiding oxygen – like covering up chopped apples in water or sugar.

Answered by Andy Extance for Brain Dump in How It Works issue 139.

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