This experiment was developed by America’s Test Kitchen Kids. When avocados are left out after being cut open, they turn brown. (Yuck!) Can you keep them deliciously bright green? Find out with this simple science experiment. You can do this activity with friends or family. If you don’t have a whole lemon, you can use 3 tablespoons of bottled lemon juice. To tell if your avocado is ripe, place it in the palm of your hand and give it a gentle squeeze. If the avocado is a little soft, it’s ripe!

Safety Considerations: Uses a knife

Difficulty: Easy

Time: 5 minutes, plus 8 to 24 hours waiting time

Prepare Ingredients:

• 1 lemon
• 1 cup water
• 1 ripe avocado

Gather Equipment:

• Butter knife or chef’s knife
• Cutting board
• Small bowl
• Soupspoon
• Small plate

1. Use knife to cut lemon in half crosswise (not through ends). Rinse and dry knife.

2. Squeeze juice from lemon halves into small bowl. Add water to bowl.

3. Use knife to cut avocado in half lengthwise around pit. Using your hands, twist both halves in opposite directions to separate. Use soupspoon to scoop out pit. Discard pit.

4. Place 1 avocado half, cut side down, in bowl with lemon juice mixture. Place second avocado half on small plate, cut side up. Set bowl and plate in a spot where they won’t be disturbed.

5. Let avocado sit for at least 8 hours or up to 24 hours.

6. Meanwhile, make a prediction: What do you think each avocado half will look like after 8 hours? Will they look the same? Different? How so?

7. Time to observe! Gently turn over avocado half in lemon juice mixture. Do the 2 halves look the same? Different? How so?

8. Eat your avocado! Both avocado halves are safe to eat — use a spoon to gently scrape off any brown parts. The flesh underneath should be green. Will you use the avocado to make guacamole or avocado toast? Will you put it on top of a salad ...or a taco?

The Results

When you cut open an avocado, air touches the green flesh inside. After a few hours, the green avocado starts to turn brown. Why does this happen? It comes down to chemistry: Molecules inside the avocado flesh react with oxygen in the air. That reaction, called oxidation, creates new brown-colored molecules.

How can you stop cut avocados from turning brown? Acid to the rescue! Acids are found in ingredients such as lemon juice, lime juice, and vinegar. They are a kind of molecule called antioxidant. “Anti” means “against” and “oxi” means “oxygen,” so antioxidants are molecules that help prevent the oxidation reaction that turns avocados brown.

Keeping the avocado flesh under water also helps prevent too much oxygen from touching it. That’s why this combination of water and lemon juice works so well to keep the avocado green.