Browning Apples Experiment
I love going apple picking in the fall/autumn. But, have you ever cut some nice, fresh apple slices, only to see it start to turn brown before you’ve even had a chance to eat? The browning process happens quickly and while it doesn’t affect the flavor right away, it can make your once beautiful apple seem less appealing. Why do apples brown like that? Can we prevent it? Let’s do an experiment and find out!
How to Keep Apples from Browning
A Science Experiment on Oxidation
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Why do Apples turn brown?
Apples turn brown because of a chemical process called oxidation, this is a natural process that affects many fruits and vegetables.
When you cut into an apple, you expose its flesh or white center to oxygen. This oxygen reacts with enzymes in the apple, particularly polyphenol oxidase, leading to a chemical reaction called oxidation. The result is the production of melanin, the same pigment responsible for browning in bananas and even the darkening of certain metals like copper. While the brown color is not harmful, it can make apples seem less appetizing.
Did you know that different apples brown faster than others due to their enzyme levels and how much phenolic content they contain. For example, apples like Granny Smith tend to brown slower because they have lower levels of phenolic compounds, while apples like Red Delicious may brown more quickly. Understanding this can help us explore ways to delay the oxidation process.
Vocabulary Check
OXIDATION: a chemical reaction that occurs when substances interact with oxygen. You will see this same process in fruits and vegetables like – bananas, potatoes, pears and avocados. Oxidation can change not only the appearance but also the texture and flavor of foods.
If you tried the pumpkin preservation experiment, you know that bacteria and fungi break down pumpkins once they are cut, causing them to rot. The concept is similar to oxidation in apples. Once exposed to air, the fruit undergoes changes that can affect its longevity. However, while we aim to preserve pumpkins from microbial decay, with apples, we’re more focused on preventing or delaying the oxidation process so they retain their crispness and look more appealing to eat.
How to Keep Apples from Turning Brown?
In this experiment, we’ll test various food-safe methods for preventing apples from browning. We’ll compare how each method works and whether it can keep the apples fresh-looking for longer. You can try this experiment at home or in school with your students to see which methods work best!
Supplies
Apples – you will need 4 slices per group of kids for this experiment
Lemon juice
Saltwater solution (1/2 teaspoon of salt in 1 cup of water)
Honey water solution (1 tablespoon of honey in 1 cup of water)
Lemon Lime Soda
Knife or apple cutter
4 bowls
Paper Plates
Directions
First, cut the Apples. Begin by cutting each apple into slices. Try to ensure each slice is a similar size for accurate comparison. Using an apple cutter is a fun way to do this for kids.
Next, fill the four bowls with the different preservation solutions (there are our experiment variables) and label each bowl so you don’t mix them up. Solution 1 is lemon juice, solution 2 is saltwater, solution 3 is honey water and solution 4 is lemon lime soda.
Place one slice of apple in each solution and let them soak for 5 minutes.
While they are soaking, label your plates with the each of the four solutions.
Now it is time to observe. After soaking, lay the slices out on a plate and monitor them for any changes. Record the time that you set out the apples. Now take notes at regular intervals to track how much the apples change. We found it helpful to take pictures and tracked our apples over 2 days.
Once you conclude your observations, it is time to compare the results. Here are our results:
Over the course of a few hours or days, compare the color of the apples. Which method was most effective in preventing browning? Did any solutions actually speed up the browning?
For fun we soaked a second slice in each to check how the methods affected the taste of the apples.
Apple Browning Experiment Results
Our results were surprising, all of these methods were pretty impressive. We ended up leaving the apple slices out for more than 24 hours before we saw any change. The most effective was the lemon juice, followed closely by the honey and salt. The soda was the least effective but still really good. If you were slicing apples to put on a fall fruit tray any of these methods would work beautifully to preserve the apples and keep them looking great.
But what about our taste test? Taste wise I would choose the honey. I think it enhanced the flavor the best, followed in order by the soda, salt and lemon juice last because it made the slices sour.
The Science
Lemon Juice
Lemon juice is highly effective because it contains ascorbic acid (vitamin C), which slows the oxidation process by lowering the pH on the apple’s surface. However, the tart flavor of lemon may not be desirable if you’re planning to eat the apple slices on their own.
Saltwater
A saltwater solution helps to draw out some of the moisture, which slows down the oxidation process. The salt acts as a preservative by preventing oxygen from reacting with the apple’s flesh. Be sure to rinse the apples before eating to avoid a salty taste.
Honey Water
Honey contains natural antioxidants that can slow oxidation. Soaking apples in a honey water solution is a food-safe method that doesn’t leave a strong taste and works well to keep them fresh.
Lemon Lime Soda
The lemon lime soda contains citric acid and prevents the formation of melanin in the same way that lemon juice does. However, it has a neutral flavor and is a great choice for preventing browning.
Understanding the science of oxidation is key to preventing apples from turning brown. Through this apple oxidation experiment, we explored different methods for keeping cut apples looking fresh, including lemon juice, saltwater, and honey water and soda. Each method works by slowing down the chemical reaction that causes browning, with varying levels of success.
Next time you cut an apple, try one of these simple solutions to enjoy fresh-looking slices longer. This is a great idea lunchboxes! Whether it’s for a party or a healthy snack, knowing how to preserve apples will make your fruit look and taste better for longer.
Want to try more apple experiments? Try Apple Volcanoes!