Why does my apple go brown?

The answer, for parents

Short answer: Cutting an apple breaks its cells, and an enzyme helps oxygen from the air turn the slice brown.

An apple is made of tiny parts called cells. A knife breaks open many of them. The insides of the cells spill out and mix together. Inside the cells is a helper chemical called an enzyme. It waits for a job. When the cells break, the enzyme meets other chemicals and the air.

Air has a gas called oxygen. The enzyme helps oxygen change the apple's chemicals. They make a brown colour. This takes a little time, so the cut apple turns brown. It is a bit like rust on a nail. Both use oxygen. But it is not the same. The apple goes brown because of its own enzyme.

In the lesson, your child puts this cause-and-effect chain in order: Cutting breaks open the cells → The enzyme meets oxygen in the air → The enzyme helps oxygen change the chemicals → A brown colour forms → The slice looks brown.

What if we squeeze lemon juice on the apple? Lemon juice is sour and has vitamin C. It slows the enzyme down, so the apple stays pale for longer.

Do other foods go brown too? Yes. Bananas, pears and potatoes go brown too. They have helper enzymes just like apples.