Sometimes you need only part of an avocado for your taco or toast. But if you save the rest for later, your avocado will turn brown (no!). Can you keep it fresh and green? Find out in this kitchen science experiment.
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Use knife to cut avocado into 2 halves and use soupspoon to remove pit. Discard pit.
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.
Time to observe! Gently turn over avocado half in lemon juice mixture. Do the 2 halves look the same? Different? How so?
When you cut open an avocado, air touches the green flesh inside. After a few hours, the green avocado starts to turn brown—yuck!
Why does this happen? It comes down to chemistry: Molecules inside the avocado flesh react with oxygen in the air. That reaction, called oxidation (“ox-ih-DAY-shun”), 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 an antioxidant (“ann-tee-OX-ih-dent”). “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.
What happens if you repeat this experiment with a different acidic ingredient instead of the lemon juice? Try using vinegar or lime juice instead. Are your results the same? Which acid prevents browning the best?
Will acids prevent other fruits from turning brown? Try repeating the experiment using apples, pears, bananas, or other fruits that you’ve noticed turn brown once they’re cut.
Did you know the avocado pit is actually the seed of the avocado tree? Instead of throwing away the avocado pit in step 2, use it to grow a new plant! Here’s how to do it:
Refill water as needed so that bottom ½ inch of pit is always under water.
You should see roots and a stem sprout out of pit in about six weeks.
When roots and stem are several inches long, follow directions here to plant your avocado tree in soil and watch it slowly grow bigger and bigger.