Test what keeps apples from browning in this apple oxidation experiment! Grab the free worksheet and guide your kids through the scientific method. Perfect for the fall!
My kid sliced an apple for his snack, got distracted, and came back twenty minutes later to find it looking like something from a science experiment. Which, it turns out, it was.
That’s exactly what we decided to do – turn apple browning into an actual apple oxidation experiment. And my kids were way more into it than I expected.
In this apple-browning experiment, we test a handful of common kitchen liquids to find out which one does the best job of preventing apples from turning brown. Lemon juice? Salt water? Vinegar? The winner might surprise you. (It surprised us.)
Along the way, your kids get a hands-on walk-through of the scientific method – observation, hypothesis, experiment, results, conclusion. It’s one of those activities that feels like play and works like a real science lesson. Grab the free apple oxidation experiment worksheet below to record everything.
Why Do Apples Turn Brown?
When you slice an apple, an enzyme called polyphenol oxidase (PPO) in the apple’s cells is exposed to oxygen in the air. The PPO reacts with oxygen to produce melanin, which is the brown pigment you see. This process, called oxidation, occurs in any fruit with PPO when the skin is broken.
It’s the same reason bananas, pears, and avocados darken after you cut them. The apple isn’t going bad; it’s just reacting to the air.
So how do you stop it? That’s what this experiment is all about.
The Scientific Method
Before jumping in, walk your child through the scientific method. It takes about five minutes and makes the whole experiment feel more intentional, especially if you’re doing this for a science fair.
Observation: Apple slices turn brown when you leave them out.
Question: What keeps an apple from turning brown?
Hypothesis: Dipping the apple slices in a liquid will slow the browning process.
Have your child predict which liquid will work best and write it down on the free worksheet before you start. This is important – the whole point is to form a guess before you see the results.
How to Set Up the Apple Oxidation Experiment
Materials:
- 1 apple
- A knife (adult handles this part)
- Several small containers or bowls
- Paper and a marker for labels
- A variety of liquids — we used:
- Plain water
- Salt water
- Lemon juice
- Vinegar
- Milk
- Baking soda solution
- The free apple oxidation worksheet (link below)
- Feel free to swap in whatever you have around the house. That’s part of the fun — the experiment works with whatever liquids your kids want to test.
Directions:
Step 1: Set Up Your Labels
Cut out small pieces of paper and write the name of each liquid you’re testing. Include one labeled “air” – that’s your control, the apple slice with nothing on it.
Set the labels next to their corresponding containers before you pour anything. You don’t want to forget which bowl is which later.
Having a control variable is necessary so you can compare it with the other apples submerged in various liquids.
Step 2: Pour the Liquids
Pour each liquid into its own container. Use roughly the same amount in each one so the results are comparable.
For the salt water, dissolve a generous pinch of salt into a cup of water and stir until dissolved.
For the baking soda solution, dissolve a teaspoon of baking soda in a cup of water.
Step 3: Slice and Submerge
Slice the apple into similarly sized pieces. You want them consistent, so you’re comparing apples to apples (sorry… not sorry). Drop or place one slice into each container so it’s fully covered. Place the control slice on a plate in the open air.
Step 4: Make Predictions
While everything soaks, have your child fill out the hypothesis section of the free worksheet. Which liquid do they think will keep the apple freshest? Why?
Step 5: Check In Every Hour
Leave the apple slices for up to 5 hours, checking at 1, 3, and 5 hours. Each time, have your child observe and record:
- How brown is each slice?
- Has the color changed since the last check?
- Any difference in texture?
Your child can draw what the apple slices look like directly on the worksheet.
Step 6: Compare and Record Final Results
After 5 hours, take the slices out and compare them side by side. Record which browned the fastest and which held up best.
You can also gently press on each slice to feel the difference in texture – that part is surprisingly interesting.
Our Results
After 3 hours, here’s what we found:
The salt water slice was barely browned at all. It also had a spongy texture. The salt drew moisture out of the cells through osmosis, which interfered with oxygen reaching the apple’s surface.
Lemon juice was a close second. The ascorbic acid (Vitamin C) in lemon juice reacts with oxygen before the oxygen can react with the PPO enzyme, thereby significantly slowing browning.
Milk actually did better than we expected. The apple stayed fairly light. A future experiment could test whether the fat content in the milk makes a difference.
Plain water helped a little, but not much. It slightly slows oxygen exposure, but water alone isn’t a great barrier.
Vinegar surprised us – it actually seemed to speed up the browning instead of slowing it down. Vinegar is acidic, and we expected it to behave like lemon juice. We’re still not entirely sure whether this was an experimental error or something else at play. Would love to hear your results in the comments.
Baking soda made the apple brown faster too. Alkaline (high pH) liquids, like a baking soda solution, contain higher amounts of available oxygen, so coating the apple actually brought more oxygen to the surface and accelerated the reaction.
Winner: Salt water. Though you’d want to rinse it off before eating if you don’t want a salty apple.
The Science Behind the Results
Why Lemon Juice Works
Lemon juice contains ascorbic acid (Vitamin C). Oxygen reacts with ascorbic acid first before it can reach the PPO enzyme in the apple. Once the ascorbic acid is used up, browning resumes. That’s why lemon juice buys you time rather than permanently stopping browning.
Why Salt Water Works
Salt water surrounds the apple cells, creating a higher-concentration environment than the cells’ interiors. Through osmosis, water moves out of the cells to try to equalize the salt concentration. That water-and-salt layer on the surface physically impedes oxygen from reaching the apple’s flesh, slowing the reaction.
Why Vinegar and Baking Soda Backfire
Even though vinegar is acidic (like lemon juice), it doesn’t contain ascorbic acid, so it can’t do the same job of intercepting oxygen. Baking soda, being alkaline, introduces more oxygen to the surface, which is the opposite of what you want.
What Else Turns Brown Like This?
Bananas, pears, avocados – anything with PPO will do the same thing when cut. You can test this too. Try the same liquids on a pear and see if salt water wins again.
Extensions and Follow-Up Experiments
Once your kids finish this one, there’s a lot of room to keep going:
- Test more liquids – honey, orange juice, pineapple juice, or even club soda
- Test different apples – do some varieties brown faster than others?
- Vary the timing – does a 30-second dip work as well as a 5-minute soak?
- Test cut vs. bruised – does a bruised apple brown faster than a sliced one?
Each of these is its own mini-experiment using the same scientific method framework.
More Apple Science and Fall Activities
If you’re doing a whole apple unit this fall, Education.com has a huge collection of apple-themed worksheets and science activities – sorting, measuring, life cycles, taste tests, and more – that pair well with experiments like this one. All organized by grade level, all printable.
We like using it as a one-stop resource for seasonal units so we’re not hunting around for individual activities across a dozen different sites.
You might also love these other apple experiments right here on Mombrite:
- Apple Volcano Experiment – a baking soda and vinegar reaction inside a real apple
- Density of Apple Parts Experiment – which parts of an apple sink, and which float?
- 5 Senses Apple Activity – a great starting point for younger kids before moving to chemistry experiments
And if you’re looking for more easy science experiments for kids, we’ve got a whole list organized by topic and age.
Free Apple Oxidation Experiment Worksheet
Grab the free worksheet below to record your hypothesis, track observations at each hour, draw the apple slices, and write your conclusion. It walks your child through the scientific method so the experiment has real structure – useful whether you’re doing this at home or prepping for a science fair.
Frequently Asked Questions
Why do apples turn brown when cut?
When you cut an apple, an enzyme called polyphenol oxidase (PPO) in the apple’s cells reacts with oxygen in the air. This produces melanin, the brown pigment. The process is called oxidation.
What is the best liquid to keep apples from browning?
In our experiment, salt water worked best, with lemon juice as a close second. Salt water creates a barrier between the apple’s surface and oxygen through osmosis. Lemon juice works because its ascorbic acid (Vitamin C) reacts with oxygen before the oxygen can reach the apple’s enzymes.
Does vinegar keep apples from browning?
In our experiment, vinegar actually seemed to speed up the browning rather than slow it down. This was surprising since vinegar is acidic, but unlike lemon juice, it doesn’t contain ascorbic acid to intercept the oxygen.
Is this experiment good for science fairs?
Yes, it’s a great science fair project because it has clear independent and dependent variables, is easy to set up, and yields visually obvious results. The free worksheet helps document the process in a way that works well for a display board.
What age is this experiment for?
This experiment works well for kids ages 5 and up. Younger kids need adult help with slicing the apple. The science explanation can be simplified for preschoolers (“the air makes the apple change color”) or deepened for older kids with the full enzyme chemistry.
I hope your kids love this one as much as mine did. If you try it, I’d love to hear your results, especially if you get a different winner than we did. Drop a note in the comments below!
There were some differences with mine. The apple piece in my fresh lemon water turned brown in 30 minutes. I gusse those lemon juice I used from fridage has not fresh or almost no antioxidation and less vatimin C. I’ll sample them to test its PH.
Definitely worth testing lemon juice from a bottle versus fresh lemon! Let me know if you come to a conclusion with the PH :). Thanks!
Thank you so much for this website I am doing this exact experiment for my CREST and this website has helped me understand so much and I really liked the explanation about the lemon juice as that was helpful to.
I am so glad that it’s helpful!
Some great ideas here. I am teaching a one hour weekly science lesson to a group of adults with intellectual disabilities. Its important to use experiments that they can visualize the process and results. Adding in something edible always wins the day!