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. This a great chemistry project for St. Patrick's Day (March 17th) or to make green eggs and ham for Dr. Seuss's birthday (March 2nd). Or, you can just make green eggs to gross out your family. It's all good.
Green Egg Materials
You only need two basic ingredients for this easy food science project:
- red (purple) cabbage
Prepare the Red Cabbage pH Indicator
There are several ways you can prepare red cabbage juice for use as a pH indicator. Here's what I did:
- Coarsely chop about a half cup of red cabbage.
- Microwave the cabbage until it is soft. This took me about 4 minutes.
- Allow the cabbage to cool. You may wish to set it in a refrigerator to speed things up.
- Wrap the cabbage in a coffee filter or paper towel and squeeze the cabbage. Collect the juice in a cup.
- You can refrigerate or freeze leftover juice for later experiments.
Fry a Green Egg
- Spray a pan with cooking spray. Heat the pan over medium-high heat.
- Crack an egg and separate the egg white from the yolk. Set the yolk aside.
- In a small bowl, mix the egg white with a small amount of red cabbage juice. Did you see the color change? If you mix the egg white and red cabbage juice thoroughly then the 'white' of the fried egg will be uniformly green. If you only lightly mix the ingredients you will end up with a green egg that has white splotches. Yummy!
- 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. Note the cabbage does flavor the egg. It's not necessarily bad, just not what you expect eggs to taste like.
How It Works
The pigments in red cabbage are called anthocyanins. Anthocyanins change color in response to changes in acidity or pH. Red cabbage juice is purplish-red under acidic conditions, but changes to a blue-green color under alkaline conditions. 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 fried green egg!
Easy Blue Eggs
Green isn't the only color you can get using edible pH indicators. Another option is to use butterfly pea flowers. Steeping the flowers in boiling water produces a deep, vivid blue that is safe to add to any food or drink. While red cabbage juice has a distinctive (some would say "unpleasant") flavor, butterfly pea does not have a flavor. You can get a red cabbage at pretty much any grocery store, but you'll probably have to go online to find butterfly pea flowers or tea. It is inexpensive and it lasts practically forever.
To make blue eggs, simply prepare butterfly pea tea in advance. Mix in a few drops of the tea with the egg white to achieve the desired color. Cook the egg. You can drink or freeze any leftover tea.
Butterfly pea flower, like red cabbage juice, contains anthocyanins. The color change is different though. Butterfly pea is blue under neutral to alkaline conditions. It turns purple in very dilute acid and hot pink when more acid is added.
More Color Change Food
Experiment with other edible pH indicators. Examples of foods that change color in response to pH include beets, blueberries, cherries, grape juice, radishes, and onion. You can choose an ingredient that complements the flavor of the food in just about any color you desire. In most cases, prepare a pH indicator by soaking finely minced plant matter in boiling water until the color is extracted. Pour off the liquid for later use. A handy way to save the liquid for later is to pour it into an ice cube tray and freeze it.
For fruits and flowers, consider preparing a simple syrup. Mash or macerate the produce and heat it with sugar solution until it boils. The syrup may be used as-is or mixed in as an ingredient in recipes.