Why do apples turn brown after you cut them?

Cutting breaks open the apple's tiny cells, letting an enzyme and colour compounds in the juice meet oxygen from the air. They react together to form a brown pigment, in a process called enzymatic oxidation.

Is a brown apple still safe to eat?

Yes. Browning from oxidation only changes the colour and slightly the taste — it does not mean the apple has gone bad. You should only throw fruit away if it smells off, is slimy, or is mouldy.

Why does lemon juice stop apples from going brown?

Lemon juice is acidic and rich in vitamin C. The sourness makes the browning enzyme work much more slowly, and the vitamin C reacts with oxygen first, so the apple stays white for longer.

What other foods turn brown like apples?

Pears, bananas, potatoes and avocados brown in the same way, because they also contain the enzyme and colour compounds that react with oxygen once the food is cut or bruised.

How can I keep cut apples white for my child's snack?

Block the oxygen or slow the enzyme: squeeze on a little lemon juice, cover the slices in water or cling film, or keep them cold in the fridge. Each trick limits the apple's contact with air.

Why Apples Turn Brown

Science Interactive lesson Free to play

Fruit browning is the colour change that happens when the cut or bruised flesh of an apple (or pear, banana or potato) turns from white to brown after it meets the air. It is caused by a natural chemical reaction called enzymatic oxidation. Inside the fruit are millions of tiny cells holding sweet juice, a colourless enzyme, and colour-making compounds. When a knife slices through, it breaks the cells open, so the enzyme and these compounds spill out and touch the oxygen in the air.

Oxygen, the enzyme and the colour compounds then react together to make a new brown pigment — a bit like how iron makes rust. This is why browning matters in everyday kitchens: it changes how fruit looks and tastes, and understanding it helps families keep cut fruit fresh. Learners grasp three big ideas: that fruit is built from cells, that enzymes are tiny workers that speed up reactions, and that oxygen drives the colour change. They also learn why simple tricks work — covering the fruit blocks oxygen, while sour lemon juice (acidic, full of vitamin C) slows the enzyme down.

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What this Spark covers

A mystery on your plate

🍎➡️🟤 Science detective Why do apples turn brown? You slice an apple for snack time. You go to wash your hands… and when you come back, the white part has turned a sad brown colour! 😮 The apple is not dirty and it is not rotten. Something invisible changed it. Let's be science detectives and find out what! Tap Next to open the apple and look inside. 🔍
Tiny rooms inside

Inside, the apple is full of juice An apple is made of millions of tiny boxes called cells. Each cell is like a little water balloon full of sweet juice. Hidden in that juice are two secret things: a special helper called an enzyme, and tiny bits of food colour stuff. While the apple is whole and the cells are closed, they stay apart and nothing happens. Tap the apple's cells to peek inside each one. 0 of 4 cells opened
The knife lets air in

Cutting pops the little balloons When the knife slices the apple, it breaks open those tiny cells. The juice spills out, and now the hidden enzyme and the colour stuff can finally touch each other. But they still need one more guest to make brown… and that guest is floating all around us. Can you guess what it is? 💨 Which invisible thing in the air joins the reaction? Water 💧 Oxygen 🌬️ Sound 🔊
Air + apple = brown

This is called oxidation Oxygen from the air meets the enzyme and the colour stuff in the spilled juice. Together they make a new brown colour, a bit like rust on a bicycle. 🚲 Scientists call this reaction oxidation (say it: ox-i-DAY-shun). "Oxi" comes from oxygen! Drag the slider to let more time pass. Watch the air slowly brown the apple. Time: just cut — still fresh! 😀
Stop the brown!

How can we keep apples white? If oxygen and the enzyme cause browning, we can fight back by blocking the oxygen or slowing the enzyme. Try each trick and see what happens! Tap a trick to test it on the apple slice. 🍋Squeeze lemon juice 💧Soak in water 🧻Wrap it up tight ☀️Leave in the sun You have tested 0 tricks. Find the 3 tricks that help!
The lemon trick

Why does sour lemon work best? Lemon juice is full of vitamin C and is very sour (acidic). The sourness makes the enzyme too sleepy to work, and the vitamin C grabs the oxygen first — before it can reach the apple. Clever! 🦸 Match each helper to its job. Tap a job, then tap the helper that does it. Tap a yellow job card to start.
Detective field notes

Try this at home (with a grown-up) Now you know the secret, here are real tricks families in Singapore use. Tap each card to reveal why it works. Tap all the cards to flip them over!
You cracked the case!

🎉🍎🔬 Case solved, detective! You discovered why apples turn brown. Here's everything you learned: 🧫 An apple is full of tiny cells holding an enzyme and colour stuff. 🔪 Cutting breaks the cells and lets them mix. 🌬️ Oxygen from the air joins in — this is called oxidation. 🟤 Together they make a harmless brown colour (a bit like rust). 🍋 Lemon juice, water, or wrapping blocks the oxygen and slows the brown. A brown apple is still safe to eat — it just changed colour. Now you can amaze your family with the science of snack time! 🌟

Frequently asked questions

Why do apples turn brown after you cut them?: Cutting breaks open the apple's tiny cells, letting an enzyme and colour compounds in the juice meet oxygen from the air. They react together to form a brown pigment, in a process called enzymatic oxidation.
Is a brown apple still safe to eat?: Yes. Browning from oxidation only changes the colour and slightly the taste — it does not mean the apple has gone bad. You should only throw fruit away if it smells off, is slimy, or is mouldy.
Why does lemon juice stop apples from going brown?: Lemon juice is acidic and rich in vitamin C. The sourness makes the browning enzyme work much more slowly, and the vitamin C reacts with oxygen first, so the apple stays white for longer.
What other foods turn brown like apples?: Pears, bananas, potatoes and avocados brown in the same way, because they also contain the enzyme and colour compounds that react with oxygen once the food is cut or bruised.
How can I keep cut apples white for my child's snack?: Block the oxygen or slow the enzyme: squeeze on a little lemon juice, cover the slices in water or cling film, or keep them cold in the fridge. Each trick limits the apple's contact with air.

Why Apples Turn Brown

What this Spark covers

Frequently asked questions

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