Have you ever left some apple slices sitting around and when you look at them they’re all brown? Not the ones kids get at school, there’s a reason those don’t change color. We’ll get into that reason a little later! Today you’ll learn a quick way to make that brown color stay away from apples (not that it changes the flavor in a short while, but often people don’t like the look of it!).
Materials:
- Apple slices
- Lemon juice
- Measuring cup
- Tablespoon
- Water
- Bowl
- Plate
Procedure:
- Slice up an apple into whatever size pieces you want (have a parent show you how if you’re uncertain)
- Take half the slices and put them on the plate to observe the browning
- In the bowl, mix one tablespoon of lemon juice with a cup of cold water
- Let the remaining apple slices soak in the lemon water for 3 – 5 minutes
- Rinse the apples off with water and put them on the plate next to the unsoaked apples
- Wait at least 5 – 10 minutes and observe your apples
Explanation:
Why do apples turn brown after you slice them? There’s a process called “oxidation” that changes some parts of the apple. Like the word sounds, oxygen in the air comes into contact with the fruit and causes a chemical reaction to form that brown color. After 5 minutes, the brown doesn’t change the flavor at all. But people don’t like to see all that for some reason. Don’t let it stop you from eating them!
So why do the lemon-soaked apples not brown as easily? (They won’t stop the browning, it just slows the process) Lemon juice has citric acid in it which blocks the oxygen from reacting with the apples!
Going further:
Are there other fruits that brown when you leave them sliced and out on a plate? See if you can use this same strategy to stop those fruits from changing, too.
Another technique is to use salt instead of lemon juice. Use ½ of a teaspoon of salt dissolved in a cup of water and rinse it off after 3-5 minutes. Have you gotten apple slices in a bag from a school lunch or someplace else? If you look at the ingredients there are a couple of things to prevent the browning. One is “ascorbic acid” which does the same thing as citric acid to prevent browning.
Just remember, the browning doesn’t mean the fruit is bad! You can still eat it!
LOOKING FOR MORE science experiments? Find them here!
About the author:
Steve Davala has been teaching math and science to middle and high schoolers since 2000. He writes books, plays music, carves wood and he loves learning new things. Ask him a question at steve.davala@gmail.com.
