Why Do Apples Turn Brown?

The phone call and the lemon juice experiment

My first thought was to say "it's fine, you can eat it" and leave it there. Then I stopped, because it was a good chance to show a bit of science. I told my kid I had a magic trick. I picked up the other half of the apple and squeezed a few drops of lemon juice on the cut side. Then I said we'd wait 10 minutes and look again.

After 10 minutes, the half with no lemon juice had gone brown. The half with lemon juice looked about the same as it did when I cut it. My kid stared at the two halves and asked how I did that.

I tried to explain it the way a kid would get it. I said an apple is a bit like the little eraser in a pencil case. When the eraser gets dirty you scrape it with a knife and it's usable again. Inside the apple there's a colour-changing helper called an enzyme. When you cut the apple, there's no skin to protect it, so the enzyme starts playing with the oxygen in the air, and the two of them make brown "rust". Then my kid asked why the lemon juice works. I said the lemon has a vitamin C hero in it, and the hero grabs the oxygen before the enzyme can. If the enzyme can't find any oxygen, it can't change the colour.

My kid thought about it and said, "Next time I'll squeeze lemon on it, or eat it fast." I said eating it fast is the smartest answer, because nothing gets wasted and it tastes better anyway.

Why do apples turn brown?

The kid version is close, but here's the proper one. Apple flesh has natural compounds called phenolics, and it has an enzyme called polyphenol oxidase, or PPO. In a whole apple these are kept apart inside the cells. When you cut or bite the apple, cells break open and everything mixes. With oxygen from the air, the PPO turns the phenolics into brown pigments. It's called enzymatic browning, and Penn State Extension says it happens because cut flesh is exposed to oxygen.

It's not only apples. Pears, peaches, bananas, avocados and potatoes do the same thing when you cut them. I wrote about the same reaction in pears in my post on whether a pear goes brown when cut.

About the lemon juice, the "vitamin C hero" is the kid version. The grown-up version is that acid slows the enzyme down. A review of browning control says PPO works best around pH 5 to 7 and is inhibited below pH 3, and it lists citric acid and ascorbic acid (vitamin C) as things that lower the pH. Lemon juice does both jobs.

Is a brown apple safe to eat?

Browning by itself is about looks, not safety. The apple has reacted with air, and that's all. It may taste a little flatter, and the texture can be softer.

What matters for safety is how long the apple has been sitting out and how it was stored, and that's the same as for any cut fruit. The USDA says cut fruit should be kept in a covered container in the fridge and shouldn't stay at room temperature for more than two hours. If a cut apple smells sour or boozy, feels slimy, or has mould, I throw it out. Colour alone isn't the test.

Five ways to slow it down

I haven't tested all of these side by side myself. Where I could find people who did, I've added what they found, because the results were more mixed than I expected.

Lemon or lime juice

This is the one from my story. You can drip a few drops of lemon juice on the slices and toss them lightly. Or you can mix 1 tablespoon of lemon juice into 1 cup of cold water, soak the slices for 3 to 5 minutes, and rinse them off. Lime juice and pineapple juice work the same way. If you don't like the sour taste, pick a sweeter apple to go with it. In Food Network's test, plain lemon juice was tied for second best, and the lemon water version came third, so it does work but isn't the winner. Honestly, it also depends on how much juice you use. A little on the surface is fine, and a lot will taste like lemon.

Salt water

This one surprised me, because salt sounds like the wrong thing to put on fruit. Food Network's test put it in first place. They dissolved half a teaspoon of salt in a cup of water, soaked the apple for 5 minutes, and rinsed it, and the slices browned the least and didn't taste salty. That's the amount to use. If you sprinkle on a lot of salt, the apple will taste like a pickle, so go easy. Rinse the slices before you eat them.

Lemon-lime soda

If you've got half a bottle of Sprite or ginger ale going flat in the fridge, don't tip it out. Soak the slices for 3 to 5 minutes and lift them out. If you like a bit of fizz and sweetness, you can skip the rinse. Some people use sugar-free soda water instead, which is easier on the sugar. I'd guess it does less, since plain soda water doesn't have the citric acid that lemon-lime soda has, but I haven't tested it. The Kitchn tried it, and the slices looked fresh for nearly three hours on a plate and nearly six hours in a bag. They also said it isn't worth buying soda just for this, since cheaper methods work better.

The rubber band trick

This is the cute one, and it's good for taking a whole apple out of the house. Cut the apple into slices with the skin on and don't separate them. Put the pieces back together like a puzzle and wrap a rubber band around the middle, so it looks like an uncut apple. When it's time to eat, you pull the slices apart. It's great for a kid's lunch, and when a kid opens the box it looks like a whole apple. The catch is that the cut sides are still touching each other, and some people found it didn't stop browning very well. Stemilt saw more browning with the rubber band than with other methods. I'd say it's fine for a few hours, and I wouldn't count on it beyond that.

A quick hot-water blanch

This one is for apples you're about to cook or bake with, or put in a salad that's going to sit. You drop the pieces in boiling water and then rinse them in cold water. The heat stops the enzyme, so the apple won't go brown. Some recipes say to boil for five minutes, but that's a long time, and the apple ends up soft. The National Center for Home Food Preservation says to steam blanch apple slices for only 1 1/2 to 2 minutes when freezing them. Either way the texture goes soft, so I wouldn't do this to an apple you want to eat as a crunchy snack.

There's also the vitamin C method that food preservation experts use. The NCHFP says to dissolve half a teaspoon of ascorbic acid powder in 3 tablespoons of water and sprinkle it over the fruit, and crushed vitamin C tablets also work. It's more effort than lemon, but it doesn't change the taste.

A few extra tips

The type of apple makes a big difference. A University of Missouri article says Granny Smith and Cortland are low-browning apples, Golden Delicious is in the middle, and Red Delicious browns a lot. A study of 14 cultivars also found Granny Smith and Cripps Pink browned the least. Cripps Pink is the apple sold as Pink Lady in Australia. Not every study agrees, though. A 2026 Indian study rated Golden Delicious the most resistant of the six it tested, so I wouldn't treat any one ranking as final. If you want to know which apples are sweet as well, I ranked them in which apple is the sweetest.

Use a clean knife. I've read that leftover bits on an old blade can make apples brown faster, but I haven't found a solid source for it, so take that one lightly. What I can say is that a clean knife never hurts.

After you've treated the slices, put them in a sealed bag or container, squeeze out as much air as you can, and keep them in the fridge. Cold slows the enzyme, and less air means less oxygen. That's what the review I mentioned says about temperature and oxygen too.

How I explain it to kids

Kids ask why the apple is changing colour all the time, so I've got a few things I say. When we're eating an apple, I say, "Look, the apple is secretly rusting! Inside there's a shy little phenol and a bit of oxygen, and they're holding hands and playing a game." When we're doing a little keeping-fresh experiment, I say, "Let's give the apple an invisible cloak. If we put some lemon juice on it or soak it in light salt water, the oxygen can't find it, and the apple stays white." And when we're in the supermarket or the kitchen, I point at a potato. "See, the potato went that colour after we cut it too. It has the same colour secret as the apple."

Does this work on other fruit?

Yes. All of these tricks work on pears, bananas and avocados, because it's the same reaction. I'd still pick the method to suit the fruit. Salt water works for a pear, and for an avocado I wrote up what works in my post on avocados in season. For more on what else goes on inside an apple, there's my post on why apples explode in the microwave.

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