The Egg Lab
Invite your child to crack an egg on a white plate. Together, explore and examine the egg and then draw and identify each part, using its correct scientific name, on a piece of paper.
Egg proteins change when you heat them, beat them, or mix them with other ingredients. Understanding these different processes can help you understand the make-up of eggs and the roles that eggs can play in our bodies and in our food. Proteins are made of long chains of amino acids. The proteins in an egg white are called globular proteins, which means that the long protein molecule is curled up into a spherical shape. A variety of weak chemical bonds keep the protein together as it floats in the water that surrounds it.
When you apply heat to an egg, you agitate the floating egg-white proteins. They bounce into the surrounding water molecules and bump into each other. All this activity breaks the weak bonds that kept the protein curled up. The egg proteins uncurl and bump into other proteins that have also uncurled. New chemical bonds form—connecting one protein to another.
After bouncing and bonding, the egg proteins form a network of interconnected proteins. The water in which the proteins once floated is captured and held in a protein web, transforming the liquid egg white to a solid. But if you leave eggs at a high temperature for too long, too many bonds form and the whites become rubbery.
Let’s apply it
Practice what you’ve learned about heating eggs by making an omelet, deviled eggs or flan. [hyperlink to recipes]
When you beat raw eggs you incorporate air bubbles into the water-protein solution. Adding air bubbles to egg whites unfolds the egg proteins in the same way as heat.
To understand why introducing air bubbles makes egg proteins uncurl, you need to know a basic fact about the amino acids that construct proteins. Some amino acids are attracted to water; they’re hydrophilic, or water-loving. Other amino acids are repelled by water; they’re hydrophobic, or water-fearing.
Egg-white proteins contain both hydrophilic and hydrophobic amino acids. When the protein is curled up, the hydrophobic amino acids live in the center (away from the water) and the hydrophilic ones live on the outside (closer to the water).
Practice what you’ve learned about egg proteins by asking your child to draw an interpretation of what hydrophobic and hydrophilic amino acids look like—and where they live inside an egg-white protein.
A thrilling kitchen experiment
This activity involves your child removing the shell of an egg using vinegar. If you haven’t already, we recommend looking over the anatomy of an egg with your child first so that she can visualize and understand the interworking of the egg before doing this activity. As much as possible, serve only as a guide for your child and allow her to move independently through this experiment.
Note: it will take at least 24 hours before the shell is removed, so don’t expect immediate results!
What you’ll need
• vinegar (at least 16 ounces)
• raw eggs (as many as you want to de-shell)
• a few glasses
Prepare the workspace for your child, making sure all ingredients and tools are easily accessible to her.
Invite your child to select a glass and an egg, placing the egg gently inside the cup.
Have her carefully pour enough vinegar into the glass to just cover the egg.
If she is de-shelling more than one egg, repeat the above steps for all eggs.
Move the egg glasses to a safe place and start practicing patience!
Activity suggestion: keep a running “egg log” with your child, observing the eggs after 15 minutes; 45 minutes (by this time you should see bubbling in the glass); several hours; 12 hours; 24 hours and so on—noting the changes in a notebook or on a piece of paper. Allow your child to relay her observations to you and ask her questions to direct her continued examinations.
After 24 hours, have your child remove the eggs from the vinegar by pouring the liquid into another cup and catching the egg in her hand. Remind her that the egg is very fragile.
By this point, you may be able to rub the shell off with your fingers. Let your child try this very gently. Or, depending on the egg, it may have already shed its shell.
If the egg is not fully de-shelled, gently place the egg in a new cup, pouring vinegar over it once more, and let it soak for another 24 hours.
Once you have de-shelled the eggs, ask your child to examine the newly naked egg. What do you notice about it? How does this egg look different from yesterday? What do you think happened to the shell? How do you think it’s staying together without a shell? (If she needs some guidance here—direct her to think about the anatomy of the egg—what is on the outside? What does it do?) How does it feel compared to a regular egg? Is it heavier or lighter? Why do you think that is? (The egg will be slightly heavier—some of the vinegar and water will have moved through the semi-permeable membrane into the egg. Tell your child this is called osmosis.) Does it smell different? What does it smell like?
Experiments with your shell-less eggs
Your child probably will have noticed that her egg is kind of rubbery. Ask her: How far above the table can you drop your egg without it breaking? Start at one inch, then try two inches, and so on. Keep in mind that eventually the membrane will break and things will get messy, so you may want to do this experiment outside.
Ask your child: What do you think will happen if we put the egg in a cup of water? The inside of an egg is around 90% water. If you put the egg in a cup of (100%) water, the water will move inside the egg through the membrane to equalize the amount of water inside and outside of the membrane. Guide your child to observe the changes in the size of the egg over the course of 24 hours. Explain to your child that this process is called osmosis. Osmosis equalizes—or makes the concentration of water on both sides of the egg membrane the same. Ask her: How will the egg change if we leave it in the water for a long time? Why will that happen?
Your child can color the inside of her egg by soaking it in water with food coloring. This is also a fun way to watch osmosis work—moving the color through the membrane and not just coloring the outside.
Now that your child is familiar with osmosis, ask her: Do you think we could make the egg shrink? By putting the egg in a liquid with only a little bit of water, your shell-less egg will shrink! Invite her to put an egg in a glass and cover it with corn syrup.
Let the egg sit in the corn syrup for at least 24 hours, monitoring and noting the changes in your egg log. You will see the egg shrink and begin to look “baggy.” The longer it sits, the more “raisin-like” it will become, although the yoke will remain inside. Guide your child to make observations about how the time the egg sits in the liquid affects how it looks.
Invite your child to take the egg out of the liquid and examine it with her hands whenever she wants.
Ask your child: How do you think this is happening? Then explain that once the egg is in the syrup, the water inside the egg moves back out to equalize the water concentration. Osmosis.
Ask your child: Do you think we could change the egg back to how it used to be? How might we do that?
You can reverse the process by putting the egg back in a cup of water. The water will move across the membrane and fill the egg again.