Kids, how can adding something purple to something white make something green? Red cabbage juice contains a natural pH indicator that changes color from purple to green under basic (alkaline) conditions. You can use this reaction to make a fried green egg. First, with the help of an adult partner, prepare the red cabbage pH indicator. 1. Coarsely chop about a half cup of red cabbage. 2. Microwave the cabbage in a bowl until it is soft (about 4 minutes). 3. Allow the cabbage to cool in the bowl. 4. When cool, collect the juice in a cup. You can get more juice by wrapping the cabbage in a coffee filter or paper towel and squeezing.
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
Now, have your adult partner fry an egg. 1. Spray a pan with cooking spray. Heat the pan over medium-high heat. 2. Crack an egg and separate the egg white from the yolk. Set the yolk aside. 3. In a small bowl, mix the egg white with a small amount of red cabbage juice. Did you see the color change? The more you mix, the more uniform the green color will be. 4. Add the egg white mixture to the hot pan. Set the egg yolk in the middle of the egg. Fry it and eat it like you would any other egg. Yum!
Here is how it works. The pigments in red cabbage are called anthocyanins. These pigments change color in response to changes in pH, which is a measure of how acidic or basic something is. Red cabbage juice is purplish-red under acidic conditions (pH less than 7), but changes to a blue-green color under alkaline conditions (pH greater than 7). Egg whites are alkaline (pH ~9) so when you mix the red cabbage juice into the egg white the pigment changes color. The pH does not change as the egg is cooked so the color is stable. It's also edible, so you can eat the fruits of your labor!
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Kathleen Carrado Gregar, PhD, Argonne National Labs
[email protected]
February 2009
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References: Dr. Anne Marie Helmenstine at http://chemistry.about.com/od/chemistryhowtoguide/a/friedgreenegg.htm.
For a video see http://www.metacafe.com/watch/938777/green_egg_trick/
