Why does a cut apple turn brown — and can you stop it?
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After you watchWhy does a cut apple turn brown — and can you stop it?
The short answer
Cutting an apple mixes an enzyme, apple compounds and oxygen that start reactions producing brown pigments. Lemon juice can slow further browning through acidity and vitamin C, but it does not reliably erase mature brown pigment.
Try this next
- How would starting the lemon treatment earlier change the result? Make a prediction and explain what you would keep the same in a fair comparison.
The whole story
How it works
Polyphenol oxidase speeds oxidation of phenolic compounds into quinones, which can form brown pigments. Acid slows enzyme activity; vitamin C can reduce early quinone products. Those effects are most useful before pigment accumulates.
What people get wrong
Slowing a reaction is different from undoing its finished products. Lemon does not permanently stop browning or return every already-brown slice to its original color.
The catch
Lemon changes flavor and delays browning for a limited time. Apples, treatment concentrations and storage conditions vary. Browning alone is not a complete test of food freshness.
Questions kids ask
Why does a cut apple turn brown — and can you stop it?
Cutting an apple mixes an enzyme, apple compounds and oxygen that start reactions producing brown pigments. Lemon juice can slow further browning through acidity and vitamin C, but it does not reliably erase mature brown pigment.
What does the experiment compare?
Predict whether lemon added after brown pigment has already formed erases old patches or mostly slows further browning, then compare treated and untreated slices over time.
What is this model leaving out?
Lemon changes flavor and delays browning for a limited time. Apples, treatment concentrations and storage conditions vary. Browning alone is not a complete test of food freshness.
Talk about it
- If both slices already have brown patches, will adding lemon erase the old brown or mainly slow new browning?
- What changed in the pictures that supports your idea?
- How would starting the lemon treatment earlier change the result?
For grown-ups
The illustrated late-treatment test distinguishes early oxidation products from mature polymeric pigment. Ascorbate can reduce quinones, but cannot be relied upon to reverse established browning. Lower pH can reduce PPO activity; effects depend on cultivar, dose and storage.
Keep going
What else makes you wonder?
- How would starting the lemon treatment earlier change the result?
- What would you change in the experiment next?