Why does a cut apple turn brown?

What BBN said about it

1. 

   Dr. Nina Byte · Tech & Science CorrespondentChip asked me why a cut apple turns brown. I have three PhDs, and this is my job now.

2. 

   Dr. Nina Byte · Tech & Science CorrespondentStep one. This is an apple. When you cut it, air reaches the inside.

3. 

   Chip Darnell · U.S. News AnchorSo the apple is just sitting there, minding its own business, and then boom, oxygen shows up like an uninvited guest at a potluck.

4. 

   Dr. Nina Byte · Tech & Science CorrespondentStep two. Inside the apple is a helper chemical called an enzyme. Per Wikipedia, it reacts with oxygen in the air.

5. 

   Chip Darnell · U.S. News AnchorThe enzyme is the ride operator! He's got the little lever and a cigarette behind his ear!

6. 

   Dr. Nina Byte · Tech & Science CorrespondentStep three. That reaction makes new brown-coloured stuff. It is a bit like the apple getting a tan.

7. 

   Chip Darnell · U.S. News AnchorRight, so the operator gets bored, spins everybody too fast, and the whole ride goes brown with regret.

8. 

   Dr. Nina Byte · Tech & Science CorrespondentNo ride. No operator. Air, enzyme, brown. Please.

9. 

   Chip Darnell · U.S. News AnchorOkay. But why does lemon juice stop it?

10. 

    Dr. Nina Byte · Tech & Science CorrespondentThat is actually the right question. Lemon juice is sour, so it is acidic, and acid slows down the browning enzyme.

11. 

    Dr. Nina Byte · Tech & Science CorrespondentPer Wikipedia, acids like lemon juice slow enzymatic browning. Chip, that was genuinely smart.

12. 

    Chip Darnell · U.S. News AnchorSo the lemon is the guy who shuts down the Tilt-a-Whirl for being sour. Does he get a fair pass?